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Crystals, Volume 8, Issue 2 (February 2018)

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Cover Story (view full-size image) In this mini-review (Crystals 2018, 8, 83), Gu, Kirillov and co-workers discuss the selected [...] Read more.
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Editorial

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Open AccessEditorial The Many Facets of Diamond Crystals
Crystals 2018, 8(2), 72; https://doi.org/10.3390/cryst8020072
Received: 24 January 2018 / Revised: 24 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
This special issue is intended to serve as a multidisciplinary forum covering broad aspects of the science, technology, and application of synthetic and natural diamonds. This special issue contains 12 papers, which highlight recent investigations and developments in diamond research related to the
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This special issue is intended to serve as a multidisciplinary forum covering broad aspects of the science, technology, and application of synthetic and natural diamonds. This special issue contains 12 papers, which highlight recent investigations and developments in diamond research related to the diverse problems of natural diamond genesis, diamond synthesis and growth using CVD and HPHT techniques, and the use of diamond in both traditional applications, such as mechanical machining of materials, and the new recently emerged areas, such as quantum technologies. The results presented in the contributions collected in this special issue clearly demonstrate that diamond occupies a very special place in modern science and technology. After decades of research, this structurally very simple material still poses many intriguing scientific questions and technological challenges. It seems undoubted that diamond will remain the center of attraction for many researchers for many years to come. Full article
(This article belongs to the Special Issue Diamond Crystals)

Research

Jump to: Editorial, Review

Open AccessArticle Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure
Crystals 2018, 8(2), 15; https://doi.org/10.3390/cryst8020015
Received: 31 December 2017 / Revised: 19 January 2018 / Accepted: 19 January 2018 / Published: 23 January 2018
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Abstract
We employed ab initio evolutionary algorithm USPEX to speed up the discovery of a novel oxynitride in the binary system of GaN-TiO2 using high-pressure synthesis. A 1:2 mixture of GaN and nanocrystalline TiO2 (anatase) was reacted under 1 GPa of pressure
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We employed ab initio evolutionary algorithm USPEX to speed up the discovery of a novel oxynitride in the binary system of GaN-TiO2 using high-pressure synthesis. A 1:2 mixture of GaN and nanocrystalline TiO2 (anatase) was reacted under 1 GPa of pressure and at 1200 °C in a piston cylinder apparatus to produce a mixture of TiO2 (rutile) and an unknown phase. From the initial analysis of high resolution neutron and X-ray diffraction data, it is isomorphic with monoclinic V2GaO5 with a unit cell composition of Ga10Ti8O28N2 with the following parameters: monoclinic, space group C2/m, a = 17.823(1) Å, b = 2.9970(1) Å, c = 9.4205(5) Å, β = 98.446(3)°; Volume = 497.74(3) Å3. Further, a joint rietveld refinement revealed two distinct regimes—A Ti-rich block and a Ga-rich block. The Ti-rich block consists of four edge-shared octahedra and contains a site which is about 60% occupied by N; this site is bonded to four Ti. The remainder of the block consists of edge linked Ti-octahedral chains linked to the TiN/TiO fragments at octahedral corners partially occupied by nitrogen. The Ga-block contains two symmetry independent octahedral sites, occupied mostly by Ga, and a pure Ga-centered tetrahedral site bonded mostly to oxygen. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Two Supramolecular Inorganic–Organic Hybrid Crystals Based on Keggin Polyoxometalates and Crown Ethers
Crystals 2018, 8(2), 17; https://doi.org/10.3390/cryst8020017
Received: 13 December 2017 / Revised: 18 January 2018 / Accepted: 19 January 2018 / Published: 23 January 2018
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Abstract
New supramolecular structures were designed in this work using large-sized polyoxometalates (POMs) and crown-ether-based supramolecular cations selected as building blocks. Two novel supramolecular inorganic–organic hybrids [(3-F-4-MeAnis)([18]crown-6)]2[SMo12O40]•CH3CN (1) and [(4-IAnis)([18]crown-6)]3[PMo12O
[...] Read more.
New supramolecular structures were designed in this work using large-sized polyoxometalates (POMs) and crown-ether-based supramolecular cations selected as building blocks. Two novel supramolecular inorganic–organic hybrids [(3-F-4-MeAnis)([18]crown-6)]2[SMo12O40]•CH3CN (1) and [(4-IAnis)([18]crown-6)]3[PMo12O40]•4CH3CN (2) (3-F-4-MeAnis = 3-fluoro-4-methylanilinium and 4-IAnis = 4-iodoanilinium) were synthesized. Crystals 1 and 2 have been characterized by infrared spectroscopy (IR) and elemental analysis (EA). Based on X-ray diffraction analysis, Crystals 1 and 2 were constructed through noncovalent bonding interactions and belong to different space groups due to the difference of the building blocks used. Supramolecular cations formed due to strong N–H···O hydrogen bonding interactions between the six oxygen atoms of [18]crown-6 molecules and nitrogen atoms of anilinium derivatives. Crystal 1 has two different supramolecular cations with an anti-paralleled arrangement that forms a dimer through weak hydrogen bonding interactions between adjacent [18]crown-6 molecules. Crystal 2 has three independent supramolecular cations that fill large spaces between the [PMo12O40] polyoxoanions forming a rhombus-shape packing arrangement in the ac plane. Crystals 1 and 2 are unstable at room temperature. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Super-Lattice Structure and Phase Evolution of Pb(Lu0.5Nb0.5)O3-PbTiO3 Single Crystal with Low PbTiO3
Crystals 2018, 8(2), 50; https://doi.org/10.3390/cryst8020050
Received: 29 November 2017 / Revised: 19 January 2018 / Accepted: 20 January 2018 / Published: 23 January 2018
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Abstract
The phase diagram of the Pb(Lu0.5Nb0.5)O3-PbTiO3 (PLN-PT) binary system was previously reported based on XRD and dielectric measurements results. Unusually, the Curie temperature of PLN-PT with low PT obtained from the phase diagram is much lower
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The phase diagram of the Pb(Lu0.5Nb0.5)O3-PbTiO3 (PLN-PT) binary system was previously reported based on XRD and dielectric measurements results. Unusually, the Curie temperature of PLN-PT with low PT obtained from the phase diagram is much lower than that of PLN and PT end members, which is different from others, such as PZT. Therefore, the complex structure of PLN-PT with low PT is desired to be studied. In this work, PLN-PT single crystals with low PT were grown for the study of their super-lattice structure and phase evolution. The super-lattice reflections were identified by X-ray diffraction. Domains and their evolution by heating from room temperature to 150 °C were observed under a polarized light microscope. The phase transition from the ferroelectric phase to the paraelectric phase was determined by dielectric spectra and polarized light microscopy. A precursor/intermediate phase exhibiting pinched hysteresis loops was displayed above the Curie temperature, which originates from some polar region embedded in the non-polar matrix. The coexistence of the ferroelectric and antiferroelectric domains leads to peculiarities of the phase transitions, such as a lower Curie temperature compared with PLN and PT. The studies of the phase evolution of PLN-PT with low PT single crystal is a supplementary amendment of the PLN-PT phase diagram as previously reported. Full article
(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)
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Open AccessArticle High-Resolution Crystal Structure of RpoS Fragment including a Partial Region 1.2 and Region 2 from the Intracellular Pathogen Legionella pneumophila
Crystals 2018, 8(2), 54; https://doi.org/10.3390/cryst8020054
Received: 25 November 2017 / Revised: 17 January 2018 / Accepted: 20 January 2018 / Published: 23 January 2018
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Abstract
Legionella pneumophila RpoS (LpRpoS), an alternative sigma factor of RNA polymerase (RNAP), is essential for virulence and stress resistance. To investigate the mechanism of RpoS in the intracellular pathogen L. pneumophila, we determined the high-resolution crystal structure of the Lp
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Legionella pneumophila RpoS (LpRpoS), an alternative sigma factor of RNA polymerase (RNAP), is essential for virulence and stress resistance. To investigate the mechanism of RpoS in the intracellular pathogen L. pneumophila, we determined the high-resolution crystal structure of the LpRpoS 95–195 containing a partial region 1.2 and region 2. The structure of LpRpoS 95–195 reveals that the conserved residues are critical for promoter melting, DNA and core RNAP binding. The differences in regulatory factor binding site between Escherichia coli RpoS and LpRpoS suggest that LpRpoS may employ a distinct mechanism to recruit alternative regulatory factors controlling transcription initiation. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle Room Temperature Solid State Synthesis, Characterization, and Application of a Zinc Complex with Pyromellitic Acid
Crystals 2018, 8(2), 56; https://doi.org/10.3390/cryst8020056
Received: 31 December 2017 / Revised: 22 January 2018 / Accepted: 22 January 2018 / Published: 24 January 2018
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Abstract
The complex [Zn2(btca)(H2O)4] was synthesized with 1,2,4,5-benzenetetracarboxylic acid (H4btca) and zinc acetate as materials via a room-temperature solid state reaction. The composition and structure of the complex were characterized by elemental analyses (EA), Fourier transform
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The complex [Zn2(btca)(H2O)4] was synthesized with 1,2,4,5-benzenetetracarboxylic acid (H4btca) and zinc acetate as materials via a room-temperature solid state reaction. The composition and structure of the complex were characterized by elemental analyses (EA), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and thermogravimetric (TG) analysis. The index results of X-ray powder diffraction data showed that the crystal structure of the complex belonged to monoclinic system with cell parameters a = 9.882 Å, b = 21.311 Å, c = 15.746 Å, and β = 100.69°. In order to expand the application of the complex, the nanometer zinc oxide was prepared by using the complex as a precursor, and the effect of the thermal decomposition temperature on the preparation of the nanometer zinc oxide was studied. The results showed that the grain size of zinc oxide gradually grew with the increase of the pyrolysis temperature, the obtained nanometer zinc oxide was spherical, and the diameter of the particles was about 25 nm. Full article
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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Open AccessArticle Conductive Supramolecular Architecture Constructed from Polyoxovanadate Cluster and Heterocyclic Surfactant
Crystals 2018, 8(2), 57; https://doi.org/10.3390/cryst8020057
Received: 30 December 2017 / Revised: 12 January 2018 / Accepted: 22 January 2018 / Published: 25 January 2018
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Abstract
Proton-conductive solid electrolytes are significant for fuel-cell battery technology. Especially for use in motor vehicles, proton conductors which work at intermediate temperatures (373–673 K) under an anhydrous atmosphere are desired to improve the fuel cell stability and efficiency. Inorganic–organic hybrid supramolecular architectures are
[...] Read more.
Proton-conductive solid electrolytes are significant for fuel-cell battery technology. Especially for use in motor vehicles, proton conductors which work at intermediate temperatures (373–673 K) under an anhydrous atmosphere are desired to improve the fuel cell stability and efficiency. Inorganic–organic hybrid supramolecular architectures are a promising option for the realization of highly conductive proton conductors. Here, a hybrid layered crystal was synthesized for the first time by using an proton-containing decavanadate (V10) anion and a heterocyclic surfactant cation. A simple ion-exchange reaction led to the formation of an inorganic–organic hybrid of V10 by using dodecylpyridazinium (C12pda) as the heterocyclic surfactant. Single crystal X-ray analyses revealed that four C12pda cations were associated with one V10 anion, which was a diprotonated species forming a one-dimensional infinite chain structure through hydrogen bonds. Anhydrous proton conductivity was investigated by alternating current (AC) impedance spectroscopy in the range of 313–393 K, exhibiting a maximum value of 1.7 × 10−5 S cm−1 at 373 K. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Strain Effects in Gallium Nitride Adsorption on Defective and Doped Graphene: First-Principles Calculations
Crystals 2018, 8(2), 58; https://doi.org/10.3390/cryst8020058
Received: 12 December 2017 / Revised: 15 January 2018 / Accepted: 24 January 2018 / Published: 26 January 2018
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Abstract
Transferable, low-stress gallium nitride grown on graphene for flexible lighting or display applications may enable next-generation optoelectronic devices. However, the growth of gallium nitride on graphene is challenging. In this study, the adsorptions of initial nucleation process of gallium nitride on graphene were
[...] Read more.
Transferable, low-stress gallium nitride grown on graphene for flexible lighting or display applications may enable next-generation optoelectronic devices. However, the growth of gallium nitride on graphene is challenging. In this study, the adsorptions of initial nucleation process of gallium nitride on graphene were investigated using first-principles calculations based on density functional theory. The adsorption energies and the role of in-plane strains were calculated for different possible configurations of the adatoms on the surfaces of vacancy defect and doped graphene. Compared with the results of the gallium adatom, adsorption of the nitrogen atom on graphene was found to exhibit greater stability. The calculations reveal that the vacancy defect core enhanced the adsorption stability of the adatom on graphene, whereas the incorporation of oxygen impurity greatly reduced the stable adsorption of the gallium and nitrogen adatoms. Furthermore, the calculations of strain showed that the lattice expansion led to increased stability for all adsorption sites and configuration surfaces, except for the nitrogen adatom adsorbed over the gallium atom in Ga-doped graphene. The study presented in this paper may have important implications in understanding gallium nitride growth on graphene. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle Effect of Sorbitol Templates on the Preferential Crystallographic Growth of Isotactic Polypropylene Wax
Crystals 2018, 8(2), 59; https://doi.org/10.3390/cryst8020059
Received: 19 November 2017 / Revised: 11 January 2018 / Accepted: 22 January 2018 / Published: 26 January 2018
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Abstract
The crystallization of isotactic polypropylene wax (iPP) in the presence of different sorbitol structures was studied. Dibenzylidene Sorbitol (DBS), as well as two of its derivatives with one or two methyl groups in the DBS molecule (MDBS and DMDBS, respectively), were tested as
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The crystallization of isotactic polypropylene wax (iPP) in the presence of different sorbitol structures was studied. Dibenzylidene Sorbitol (DBS), as well as two of its derivatives with one or two methyl groups in the DBS molecule (MDBS and DMDBS, respectively), were tested as nanometer-size fibrillar templates. The early nucleation stage and crystal morphology were analyzed in Real-Time Wide-Angle X-ray Scattering (WAXS) and polarized optical microscopy (POM). It was found that the iPP crystals showed an α-phase unit cell for the three different sorbitols. However, a preferential crystal growth in the plane (040) was observed for iPP–MDBS. The macrostructure morphology of the iPP–DBS and iPP–DMDBS wax compounds was spherulitic, while nodular macrocrystals were observed for the iPP–MDBS compound. It was concluded that the MDBS template promoted a lower interface energy because of its match with the c-axis of the iPP wax crystals, whereas, in the case of the DBS and DMDBS templates, the preferential plane was the (110), characteristic of the iPP spherulitic arrangement. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Effect of the Ultrasonic Substrate Vibration on Nucleation and Crystallization of PbI2 Crystals and Thin Films
Crystals 2018, 8(2), 60; https://doi.org/10.3390/cryst8020060
Received: 18 December 2017 / Revised: 23 January 2018 / Accepted: 24 January 2018 / Published: 26 January 2018
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Abstract
Preparation of defect-free and well-controlled solution-processed crystalline thin films is highly desirable for emerging technologies, such as perovskite solar cells. In this work, using PbI2 as a model solution with a vast variety of applications, we demonstrate that the excitation of a
[...] Read more.
Preparation of defect-free and well-controlled solution-processed crystalline thin films is highly desirable for emerging technologies, such as perovskite solar cells. In this work, using PbI2 as a model solution with a vast variety of applications, we demonstrate that the excitation of a liquid thin film by imposed ultrasonic vibration on the film substrate significantly affects the nucleation and crystallization kinetics of PbI2 and the morphology of the resulting solid thin film. It is found that by applying ultrasonic vibration to PbI2 solution spun onto an ITO substrate with a moderate power and excitation duration (5 W and 1 min for the 40 kHz transducer used in this study), the nucleation rate increases and the crystals transform from 2D or planar to epitaxial 3D columnar structures, resulting in the suppression of crystallization dewetting. The effects of various induced physical phenomena as a result of the excitation by ultrasonic vibration are discussed, including microstreaming and micromixing, increased heat transfer and local temperature, a change in the thermodynamic state of the solution, and a decrease in the supersaturation point. It is shown that the ultrasonic-assisted solution deposition of the PbI2 thin films is controllable and reproducible, a process which is low-cost and in line with the large-scale fabrication of such solution-processed thin films. Full article
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Open AccessArticle Formation of Quasicrystalline Phases and Their Close Approximants in Cast Al-Mn Base Alloys Modified by Transition Metals
Crystals 2018, 8(2), 61; https://doi.org/10.3390/cryst8020061
Received: 31 December 2017 / Revised: 20 January 2018 / Accepted: 22 January 2018 / Published: 27 January 2018
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Abstract
The aim of the presented research was to study the influence of Cr, Co, Ni, and Cu additions on the formation of quasicrystalline particles in the 94Al-6Mn base alloy during casting at intermediate cooling rates. Based on the obtained results, Cu and Ni
[...] Read more.
The aim of the presented research was to study the influence of Cr, Co, Ni, and Cu additions on the formation of quasicrystalline particles in the 94Al-6Mn base alloy during casting at intermediate cooling rates. Based on the obtained results, Cu and Ni enhance quasicrystalline phase nucleation compared to the unmodified binary composition. In the case of Cu addition, formation of a quasicrystalline phase takes place along whole thickness of the prepared casting, but its fraction and morphology depends on the cooling rates present in different parts of the sample. Based on the previous works on the beneficial effect of Fe addition, a quaternary alloy containing both Fe and Cu was prepared to evaluate the effect of the simultaneous presence of these elements on the microstructure of the obtained castings. Full article
(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)
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Open AccessArticle Characterization of the PB2 Cap Binding Domain Accelerates Inhibitor Design
Crystals 2018, 8(2), 62; https://doi.org/10.3390/cryst8020062
Received: 7 December 2017 / Revised: 16 January 2018 / Accepted: 23 January 2018 / Published: 28 January 2018
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Abstract
X-ray crystallographic structural determinations of the PB2 cap binding domain (PB2cap) have improved the conformational characterization of the RNA-dependent RNA polymerase machinery (PA, PB2, and PB1) of the influenza virus. Geometrically, the catalytic PB1 subunit resembles the palm of a human hand. PA
[...] Read more.
X-ray crystallographic structural determinations of the PB2 cap binding domain (PB2cap) have improved the conformational characterization of the RNA-dependent RNA polymerase machinery (PA, PB2, and PB1) of the influenza virus. Geometrically, the catalytic PB1 subunit resembles the palm of a human hand. PA lies near the thumb region, and PB2 lies near the finger region. PB2 binds the cap moiety in the pre-mRNA of the host cell, while the endonuclease of PA cleaves the pre-mRNA 10–13 nucleotides downstream. The truncated RNA piece performs as a primer for PB1 to synthesize the viral mRNA. Precisely targeting PB2cap with a small molecule inhibitor will halt viral proliferation via interference of the cap-snatching activity. Wild-type and mutant PB2cap from A/California/07/2009 H1N1 were expressed in Escherichia coli, purified by nickel affinity and size exclusion chromatography, crystallized, and subjected to X-ray diffraction experiments. The crystal of mutant PB2cap liganded with m7GTP was prepared by co-crystallization. Structures were solved by the molecular replacement method, refined, and deposited in the Protein Data Bank (PDB). Structural determination and comparative analyses of these structures revealed the functions of Glu361, Lys376, His357, Phe404, Phe323, Lys339, His432, Asn429, Gln406, and Met401 in PB2cap, and the dissociation of the influenza A PB2cap C-terminal subdomain (residues 446–479) upon ligand binding. Understanding the role of these residues will aid in the ultimate development of a small-molecule inhibitor that binds both Influenza A and B virus PB2cap. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle Synthesis, Characterization, and Crystal Structure of a Triazine Anion Pentafluoroosmium(VI) Complex
Crystals 2018, 8(2), 63; https://doi.org/10.3390/cryst8020063
Received: 11 December 2017 / Revised: 28 December 2017 / Accepted: 23 January 2018 / Published: 29 January 2018
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Abstract
The synthesis and characterization of a novel triazine anion pentafluoroosmium(VI) complex are presented. The single crystal determination of the title compound (hereafter denoted 1) was carried out at −140 °C. Compound 1, C3F4N3OsF5,
[...] Read more.
The synthesis and characterization of a novel triazine anion pentafluoroosmium(VI) complex are presented. The single crystal determination of the title compound (hereafter denoted 1) was carried out at −140 °C. Compound 1, C3F4N3OsF5, crystallizes in the monoclinic space group, P21/n, with unit cell dimensions: a = 8.6809(17) Å, b = 7.6848(15) Å, c = 12.415(3) Å, β = 102.633(4)°, V = 808.2(3) Å3, and Z = 4. Synthesis, characterization, X-ray diffraction study along with the crystal supramolecular analysis of the title complex were carried out. The complex contains the anionic triazine unit C3N3F4 acting as a mono dentate ligand to osmium(VI) with five fluoro ligands in a slightly distorted octahedral geometry around osmium(VI) ion (osmium is denoted as Os). The C3N3F4, triazine anion ring deviates from planarity, only with the C1 being tetrahedral. The crystal lattice of the title compound displays significant intermolecular X···X interactions, namly F···F, F···N and F···C. All types of X···X bonding consolidate to form a three-dimensional network. Full article
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Open AccessArticle Dislocation Structure and Mobility in Hcp Rare-Gas Solids: Quantum versus Classical
Crystals 2018, 8(2), 64; https://doi.org/10.3390/cryst8020064
Received: 13 December 2017 / Revised: 17 January 2018 / Accepted: 20 January 2018 / Published: 29 January 2018
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Abstract
We study the structural and mobility properties of edge dislocations in rare-gas crystals with the hexagonal close-packed (hcp) structure by using classical simulation techniques. Our results are discussed in the light of recent experimental and theoretical studies on hcp 4He, an archetypal
[...] Read more.
We study the structural and mobility properties of edge dislocations in rare-gas crystals with the hexagonal close-packed (hcp) structure by using classical simulation techniques. Our results are discussed in the light of recent experimental and theoretical studies on hcp 4 He, an archetypal quantum crystal. According to our simulations classical hcp rare-gas crystals present a strong tendency towards dislocation dissociation into Shockley partials in the basal plane, similarly to what is observed in solid helium. This is due to the presence of a low-energy metastable stacking fault, of the order of 0.1 mJ/m 2 , that can get further reduced by quantum nuclear effects. We compute the minimum shear stress that induces glide of dislocations within the hcp basal plane at zero temperature, namely, the Peierls stress, and find a characteristic value of the order of 1 MPa. This threshold value is similar to the Peierls stress reported for metallic hcp solids (Zr and Cd) but orders of magnitude larger than the one estimated for solid helium. We find, however, that in contrast to classical hcp metals but in analogy to solid helium, glide of edge dislocations can be thermally activated at very low temperatures, T∼10 K, in the absence of any applied shear stress. Full article
(This article belongs to the Special Issue Quantum Crystals)
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Open AccessArticle Synthesis and Characterization of Perovskite-Type [K1−xNax]MgF3 Mixed Phases via the Fluorolytic Sol-Gel Synthesis
Crystals 2018, 8(2), 66; https://doi.org/10.3390/cryst8020066
Received: 18 January 2018 / Revised: 18 January 2018 / Accepted: 27 January 2018 / Published: 30 January 2018
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Abstract
The focus of this article is the synthesis of perovskite-type [K1−xNax]MgF3 mixed phases via the room-temperature fluorolytic sol-gel approach. Different molar ratios of K/Na were examined and analyzed by 19F MAS NMR and X-ray powder diffraction.
[...] Read more.
The focus of this article is the synthesis of perovskite-type [K1−xNax]MgF3 mixed phases via the room-temperature fluorolytic sol-gel approach. Different molar ratios of K/Na were examined and analyzed by 19F MAS NMR and X-ray powder diffraction. Starting from pure KMgF3, a systematic substitution of potassium by sodium was evidenced when replacing K by Na. As long as the amount of sodium is less than 80% as compared to potassium, spectra just show [K4−xNaxF] environments in a [K1−xNax]MgF3 mixed phase but separate structures appear when the amount of sodium is further increased. Moreover, colloidal dispersions of nanoscaled KMgF3 particles were obtained, which were used to fabricate coatings on glass slides. Thin films showed antireflective behavior and high transmittance. Full article
(This article belongs to the Special Issue Structure and Properties of Fluoride-based Materials)
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Open AccessCommunication A Study of Extended Defects in Surface Damaged Crystals
Crystals 2018, 8(2), 67; https://doi.org/10.3390/cryst8020067
Received: 7 November 2017 / Revised: 9 January 2018 / Accepted: 24 January 2018 / Published: 30 January 2018
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Abstract
We have analyzed by transmission electron microscopy silicon and GaAs crystals polished with sandpapers of different grain size. The surface damage induced a crystal permanent convex curvature with a radius of the order of a few meters. The curvature is due to a
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We have analyzed by transmission electron microscopy silicon and GaAs crystals polished with sandpapers of different grain size. The surface damage induced a crystal permanent convex curvature with a radius of the order of a few meters. The curvature is due to a compressive strain generated in the damaged zone of the sample. Contrary to what was reported in the literature, the only defects detected by transmission electron microscopy were dislocations penetrating a few microns from the surface. Assuming the surface damage as a kind of continuous indentation, a simple model able to explain the observed compressive strain is given. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Pressure-Induced Transformation of Graphite and Diamond to Onions
Crystals 2018, 8(2), 68; https://doi.org/10.3390/cryst8020068
Received: 7 December 2017 / Revised: 16 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
In this study, we present a number of experiments on the transformation of graphite, diamond, and multiwalled carbon nanotubes under high pressure conditions. The analysis of our results testifies to the instability of diamond in the 55–115 GPa pressure range, at which onion-like
[...] Read more.
In this study, we present a number of experiments on the transformation of graphite, diamond, and multiwalled carbon nanotubes under high pressure conditions. The analysis of our results testifies to the instability of diamond in the 55–115 GPa pressure range, at which onion-like structures are formed. The formation of interlayer sp3-bonds in carbon nanostructures with a decrease in their volume has been studied theoretically. It has been found that depending on the structure, the bonds between the layers can be preserved or broken during unloading. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Effect of Alginate from Chilean Lessonia nigrescens and MWCNTs on CaCO3 Crystallization by Classical and Non-Classical Methods
Crystals 2018, 8(2), 69; https://doi.org/10.3390/cryst8020069
Received: 23 December 2017 / Revised: 27 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
In our crystallization experiments, the influence of alginate from Chilean Lessonia nigrescens and functionalized multi-walled carbon nanotubes (MWCNTs) was tested through electrocrystallization (EC) and gas diffusion (GD) methods on the crystal growth of calcium carbonate (CaCO3) and their possible stabilization of
[...] Read more.
In our crystallization experiments, the influence of alginate from Chilean Lessonia nigrescens and functionalized multi-walled carbon nanotubes (MWCNTs) was tested through electrocrystallization (EC) and gas diffusion (GD) methods on the crystal growth of calcium carbonate (CaCO3) and their possible stabilization of proto-structures in amorphous CaCO3 (ACC) state through pre-nucleation clusters (PNC) essays with automatic potentiometric titrations were performed. CaCO3 crystals obtained in the in vitro above-mentioned crystallization systems were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS) and powder X-ray diffractometer (XRD). Our experimental findings showed that ALG and functionalized MWCNTs stabilized truncated and agglomerated vaterite-like particles through GD and EC methods. While, on the other hand, we obtained qualitative information about induction or inhibition of CaCO3 nucleation that was provided by potentiometric titrations. Full article
(This article belongs to the Special Issue Carbonates)
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Open AccessArticle Solvent-Free Synthesis of All Silica Beta Zeolite in the Presence of Tetraethylammonium Bromide
Crystals 2018, 8(2), 73; https://doi.org/10.3390/cryst8020073
Received: 31 December 2017 / Revised: 27 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
We report a solvent-free synthesis of all silica Beta zeolite using a cheap organic template of tetraethylammonium bromide (TEABr). The method includes mixing, grinding and heating solid raw material in the absence of water solvent but the presence of zeolite seeds. The absence
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We report a solvent-free synthesis of all silica Beta zeolite using a cheap organic template of tetraethylammonium bromide (TEABr). The method includes mixing, grinding and heating solid raw material in the absence of water solvent but the presence of zeolite seeds. The absence of water solvent significantly improves the efficiency of synthesis, while the addition of seeds remarkably enhances the crystallization rate. In addition, the use of a cheap organic template of TEABr greatly decreases the synthesis cost. The effects of the reaction compositions, including the molar ratios of NH4F/SiO2, TEABr/SiO2, and mass ratios of seeds to the silica, on the synthesis of the pure product were investigated using different temperature. Physicochemical characterizations, including XRD, SEM, TG and N2 sorption, show that the zeolitic product has good crystallinity, uniform crystals, and high surface area. Full article
(This article belongs to the Special Issue Functional Multi-Scale Crystals)
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Open AccessArticle Lattice Vibration of Layered GaTe Single Crystals
Crystals 2018, 8(2), 74; https://doi.org/10.3390/cryst8020074
Received: 12 January 2018 / Revised: 25 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
The effect of interlayer interaction on in-layer structure of laminar GaTe crystals was studied according to the lattice vibration using micro-Raman analysis. The results were also confirmed by the first principle calculations. Accordingly, the relationship between lattice vibration and crystal structure was established.
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The effect of interlayer interaction on in-layer structure of laminar GaTe crystals was studied according to the lattice vibration using micro-Raman analysis. The results were also confirmed by the first principle calculations. Accordingly, the relationship between lattice vibration and crystal structure was established. Ten peaks were observed in the micro-Raman spectra from 100 cm−1 to 300 cm−1. Eight of them fit Raman-active vibration modes and the corresponding displacement vectors were calculated, which proved that the two modes situated at 128.7 cm−1 and 145.7 cm−1 were related to the lattice vibration of GaTe, instead of impurities or defects. Davydov splitting in GaTe was identified and confirmed by the existence of the other two modes, conjugate modes, at 110.7 cm−1 (∆ω = 33.1 cm−1) and 172.5 cm−1 (∆ω = 49.5 cm−1), indicates that the weak interlayer coupling has a significant effect on lattice vibrations in the two-layer monoclinic unit cell. Our results further proved the existence of two layers in each GaTe unit cell. Full article
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Open AccessArticle Synthesis, Crystal Structure, Herbicide Safening, and Antifungal Activity of N-(4,6-Dichloropyrimidine-2-Yl)Benzamide
Crystals 2018, 8(2), 75; https://doi.org/10.3390/cryst8020075
Received: 22 January 2018 / Revised: 29 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
The compound N-(4,6-dichloropyrimidine-2-yl)benzamide (C11H7Cl2N3O) was synthesized and the corresponding structure was confirmed by 1H NMR, 13C NMR, HRMS, IR, and single-crystal X-ray diffraction. The compound crystallized in a monoclinic system with space
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The compound N-(4,6-dichloropyrimidine-2-yl)benzamide (C11H7Cl2N3O) was synthesized and the corresponding structure was confirmed by 1H NMR, 13C NMR, HRMS, IR, and single-crystal X-ray diffraction. The compound crystallized in a monoclinic system with space group P 21/c, where a = 14.9156(6), b = 16.6291(8), c = 14.4740(6) Å, β = 95.160(2)°, V = 3575.5(3) Å3, Z = 12, Dc = 1.494 g∙cm−3, F(000) = 1632, μ(MoKa) = 3.182 mm−1, final R = 0.0870, and wR = 0.2331 with I > 2σ(I). The crystal structure was found to be stabilized by intermolecular hydrogen bonding interactions N–H···O and C–H···Cl. Furthermore, the results from biological assays indicated that the compound showed a similar protective effect on metolachlor injury in rice seedlings compared to fenclorim at a concentration of 4.0 mg∙L−1. Moreover, the compound exhibited an improved antifungal activity compared to pyrimethanil against S. sclerotiorum and F. oxysporum. Potentially, these results lay the foundation for the development of novel herbicide safeners and fungicides. Full article
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Open AccessArticle A Graphene-Based Microfluidic Platform for Electrocrystallization and In Situ X-ray Diffraction
Crystals 2018, 8(2), 76; https://doi.org/10.3390/cryst8020076
Received: 16 December 2017 / Revised: 20 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
Here, we describe a novel microfluidic platform for use in electrocrystallization experiments. The device incorporates ultra-thin graphene-based films as electrodes and as X-ray transparent windows to enable in situ X-ray diffraction analysis. Furthermore, large-area graphene films serve as a gas barrier, creating a
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Here, we describe a novel microfluidic platform for use in electrocrystallization experiments. The device incorporates ultra-thin graphene-based films as electrodes and as X-ray transparent windows to enable in situ X-ray diffraction analysis. Furthermore, large-area graphene films serve as a gas barrier, creating a stable sample environment over time. We characterize different methods for fabricating graphene electrodes, and validate the electrical capabilities of our device through the use of methyl viologen, a redox-sensitive dye. Proof-of-concept electrocrystallization experiments using an internal electric field at constant potential were performed using hen egg-white lysozyme (HEWL) as a model system. We observed faster nucleation and crystal growth, as well as a higher signal-to-noise for diffraction data obtained from crystals prepared in the presence of an applied electric field. Although this work is focused on the electrocrystallization of proteins for structural biology, we anticipate that this technology should also find utility in a broad range of both X-ray technologies and other applications of microfluidic technology. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessArticle Tetra-, Penta- and Hexa-Coordinated Transition Metal Complexes Constructed from Coumarin-Containing N2O2 Ligand
Crystals 2018, 8(2), 77; https://doi.org/10.3390/cryst8020077
Received: 10 January 2018 / Revised: 29 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
Three newly designed complexes, [Cu(L)]·CHCl3 (1), [Co(L)(MeOH)]·CHCl3 (2) and [{Ni(L)(MeOH)(PhCOO)}2Ni] (3) a coumarin-containing Salamo-type chelating ligand (H2L) have been synthesized and characterized by elemental analyses, IR and UV-VIS spectra, and X-ray
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Three newly designed complexes, [Cu(L)]·CHCl3 (1), [Co(L)(MeOH)]·CHCl3 (2) and [{Ni(L)(MeOH)(PhCOO)}2Ni] (3) a coumarin-containing Salamo-type chelating ligand (H2L) have been synthesized and characterized by elemental analyses, IR and UV-VIS spectra, and X-ray crystallography. Complex 1 includes one Cu(II) atom, one completely deprotonated (L)2− unit and one crystalling chloroform molecule, the Cu(II) atom shows a square-planar geometry. Complex 2 includes one Co(II) atom, one completely deprotonated (L)2− unit, one coordinated methanol molecule and one crystalling chloroform molecule. The Co(II) atom is a distorted trigonal-bipyramidal geometry. While complex 3 includes three Ni(II) atoms, two completely deprotonated (L)2− units, two benzoates and two coordinated methanol molecules. The complexes 1 and 2 are both possess three-dimensional supra-molecular structures by abundant noncovalent interactions. But, complex 3 formed a two-dimensional supra-molecular structure by intra-molecular hydrogen bonds. In addition, the antimicrobial and fluorescence properties of H2L and its complexes 1, 2 and 3 were also investigated. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Unravelling the High-Pressure Behaviour of Dye-Zeolite L Hybrid Materials
Crystals 2018, 8(2), 79; https://doi.org/10.3390/cryst8020079
Received: 11 January 2018 / Revised: 26 January 2018 / Accepted: 29 January 2018 / Published: 2 February 2018
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Abstract
Self-assembly of chromophores nanoconfined in porous materials such as zeolite L has led to technologically relevant host-guest systems exploited in solar energy harvesting, photonics, nanodiagnostics and information technology. The response of these hybrid materials to compression, which would be crucial to enhance their
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Self-assembly of chromophores nanoconfined in porous materials such as zeolite L has led to technologically relevant host-guest systems exploited in solar energy harvesting, photonics, nanodiagnostics and information technology. The response of these hybrid materials to compression, which would be crucial to enhance their application range, has never been explored to date. By a joint high-pressure in situ synchrotron X-ray powder diffraction and ab initio molecular dynamics approach, herein we unravel the high-pressure behaviour of hybrid composites of zeolite L with fluorenone dye. High-pressure experiments were performed up to 6 GPa using non-penetrating pressure transmitting media to study the effect of dye loading on the structural properties of the materials under compression. Computational modelling provided molecular-level insight on the response to compression of the confined dye assemblies, evidencing a pressure-induced strengthening of the interaction between the fluorenone carbonyl group and zeolite L potassium cations. Our results reveal an impressive stability of the fluorenone-zeolite L composites at GPa pressures. The remarkable resilience of the supramolecular organization of dye molecules hyperconfined in zeolite L channels may open the way to the realization of optical devices able to maintain their functionality under extreme conditions. Full article
(This article belongs to the Special Issue Functional Multi-Scale Crystals)
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Open AccessArticle High Pressure Induced Insulator-to-Semimetal Transition through Intersite Charge Transfer in NaMn7O12
Crystals 2018, 8(2), 81; https://doi.org/10.3390/cryst8020081
Received: 11 January 2018 / Revised: 30 January 2018 / Accepted: 31 January 2018 / Published: 3 February 2018
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Abstract
The pressure-dependent behaviour of NaMn7O12 (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18
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The pressure-dependent behaviour of NaMn7O12 (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18 GPa, accompanied by a change in the compressibility of the system. On the other hand, the crystallographic determinations rule out a symmetry change to be at the origin of the transition, despite all the structural parameters pointing to a symmetrizing effect of pressure. Bond valence sum calculations indicate a charge transfer from the octahedrally coordinated manganese ions to the square planar ones, likely favouring the delocalization of the carriers. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Electrocrystallization of CaCO3 Crystals Obtained through Phosphorylated Chitin
Crystals 2018, 8(2), 82; https://doi.org/10.3390/cryst8020082
Received: 22 December 2017 / Revised: 31 January 2018 / Accepted: 2 February 2018 / Published: 3 February 2018
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Abstract
A phosphorylated chitin (Chi-P) derivative was synthesized and its chemical structure was verified with Fourier-transform infrared spectroscopy (FTIR), elemental analysis, and thermogravimetric techniques (TGA). The influence of Chi-P used as a solid template through in vitro electrocrystallization (EC) supported on an indium zinc
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A phosphorylated chitin (Chi-P) derivative was synthesized and its chemical structure was verified with Fourier-transform infrared spectroscopy (FTIR), elemental analysis, and thermogravimetric techniques (TGA). The influence of Chi-P used as a solid template through in vitro electrocrystallization (EC) supported on an indium zinc oxide (ITO) surface on the growth of calcium carbonate (CaCO3) was studied. CaCO3 crystals through EC essays were also compared with crystals obtained with the gas diffusion (GD) method. Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), chronopotentiometry, Raman, and powder X-ray diffractometry (XRD) characterized all resultant inorganic particles. Our findings revealed that the EC method selectively controlled the coexistence of truncate calcite and the metastable phase of vaterite. The crystals’ morphology reflects the electrostatic interaction of phosphate moieties from Chi-P onto CaCO3 crystals through both EC and GD crystallization methods. We believe that the EC method represents a viable electrochemical approach for studying different inorganic minerals and could be useful as an in vitro classical crystallization method for the design of advanced inorganic materials with desirable shapes and properties. Full article
(This article belongs to the Special Issue Carbonates)
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Open AccessArticle The Carbonate Platform Model and Reservoirs’ Origins of the Callovian-Oxfordian Stage in the Amu Darya Basin, Turkmenistan
Crystals 2018, 8(2), 84; https://doi.org/10.3390/cryst8020084
Received: 21 November 2017 / Revised: 21 January 2018 / Accepted: 29 January 2018 / Published: 4 February 2018
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Abstract
The Calloviane-Oxfordian carbonates in the northeastern Amu Darya Basin of southeastern Turkmenistan are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, brachiopods, echinoderms, foraminifera, corals, and sponge) and non-skeletal grains (intraclasts, ooids and peloids). Two facies zones, six standard
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The Calloviane-Oxfordian carbonates in the northeastern Amu Darya Basin of southeastern Turkmenistan are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, brachiopods, echinoderms, foraminifera, corals, and sponge) and non-skeletal grains (intraclasts, ooids and peloids). Two facies zones, six standard facies belts and some microfacies types were recognized, and sedimentary model “carbonate ramp-rimmed platform” was proposed and established that can be compared with the classical carbonate sedimentary models. In this model, favorable reservoirs not only developed in the intraplatform shoal of open platform, or reef and shoal on the platform margin, but also in the patch reefs, shoal and mound facies on the upper slope. The reservoir’s pore space is dominated by intergranular and intragranular pores and fissure-pore reservoirs exist with medium porosity and medium to low permeability. Sedimentary facies and diagenetic dissolution are the key controlling factors for the development of high-quality reservoirs. Full article
(This article belongs to the Special Issue Carbonates)
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Open AccessArticle Febuxostat-Minoxidil Salt Solvates: Crystal Structures, Characterization, Interconversion and Solubility Performance
Crystals 2018, 8(2), 85; https://doi.org/10.3390/cryst8020085
Received: 5 January 2018 / Revised: 2 February 2018 / Accepted: 2 February 2018 / Published: 5 February 2018
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Abstract
Three febuxostat-minoxidil salt solvates with acetone (ACE), tetrahydrofuran (THF) and isopropanol (IPA) are synthesized by solvent-assisted grinding and characterized by infrared (IR), nuclear magnetic resonance (1H-NMR), single crystal and powder X-ray diffraction (PXRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). These
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Three febuxostat-minoxidil salt solvates with acetone (ACE), tetrahydrofuran (THF) and isopropanol (IPA) are synthesized by solvent-assisted grinding and characterized by infrared (IR), nuclear magnetic resonance (1H-NMR), single crystal and powder X-ray diffraction (PXRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). These febuxostat-minoxidil salt solvates feature isostructural with the same stoichiometries (1:1:1 molecule ratio). The proton transfers from the carboxylic group of febuxostat (FEB) to imino N atom of minoxidil (MIN), which forms the motif with combined R 2 2 (9) R 4 2 (8) R 2 2 (9) graph set in the three solvates. The solvents occupy the different positions related to the motif, which results in the apparent differences in PXRD patterns before/after desolvation although they are isostructures. The FEB-MIN·THF was more thermostable than FEB-MIN·ACE and FEB-MIN·IPA relative to solvent removal from DSC patterns, which is different from the results from the solvent-exchange experiments in chemical kinetics. All three salt solvates exhibit increased equilibrium solubility compared to FEB in aqueous medium. Full article
(This article belongs to the Special Issue Novel Pharmaceutical Cocrystals and Their Applications)
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Open AccessArticle A Standard Structure for Bile Acids and Derivatives
Crystals 2018, 8(2), 86; https://doi.org/10.3390/cryst8020086
Received: 22 December 2017 / Revised: 31 January 2018 / Accepted: 1 February 2018 / Published: 6 February 2018
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Abstract
The crystal structures of two ester compounds (a monomer in its methyl ester form, with an amino isophthalic group, and a dimer in which the two steroid units are linked by a urea bridge recrystallized from ethyl acetate/methanol) derived from cholic acid are
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The crystal structures of two ester compounds (a monomer in its methyl ester form, with an amino isophthalic group, and a dimer in which the two steroid units are linked by a urea bridge recrystallized from ethyl acetate/methanol) derived from cholic acid are described. Average bond lengths and bond angles from the crystal structures of 26 monomers and four dimers (some of them in several solvents) of bile acids and esters (and derivatives) are used for proposing a standard steroid nucleus. The hydrogen bond network and conformation of the lateral chain are also discussed. This standard structure was used to compare with the structures of both progesterone and cholesterol. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Low-Temperature Lattice Effects in the Spin-Liquid Candidate κ-(BEDT-TTF)2Cu2(CN)3
Crystals 2018, 8(2), 87; https://doi.org/10.3390/cryst8020087
Received: 13 December 2017 / Revised: 29 January 2018 / Accepted: 3 February 2018 / Published: 6 February 2018
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Abstract
The quasi-two-dimensional organic charge-transfer salt κ-(BEDT-TTF)2Cu2(CN)3 is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive
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The quasi-two-dimensional organic charge-transfer salt κ -(BEDT-TTF) 2 Cu 2 (CN) 3 is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive investigations of the material’s low-temperature properties, several important questions remain to be answered. Particularly puzzling are the 6 K anomaly and the enigmatic effects observed in magnetic fields. Here we report on low-temperature measurements of lattice effects which were shown to be particularly strongly pronounced in this material (R. S. Manna et al., Phys. Rev. Lett. 2010, 104, 016403)). A special focus of our study lies on sample-to-sample variations of these effects and their implications on the interpretation of experimental data. By investigating overall nine single crystals from two different batches, we can state that there are considerable differences in the size of the second-order phase transition anomaly around 6 K, varying within a factor of 3. In addition, we find field-induced anomalies giving rise to pronounced features in the sample length for two out of these nine crystals for temperatures T < 9 K. We tentatively assign the latter effects to B-induced magnetic clusters suspected to nucleate around crystal imperfections. These B-induced effects are absent for the crystals where the 6 K anomaly is most strongly pronounced. The large lattice effects observed at 6 K are consistent with proposed pairing instabilities of fermionic excitations breaking the lattice symmetry. The strong sample-to-sample variation in the size of the phase transition anomaly suggests that the conversion of the fermions to bosons at the instability is only partial and to some extent influenced by not yet identified sample-specific parameters. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle Coupling between Spin and Charge Order Driven by Magnetic Field in Triangular Ising System LuFe2O4+δ
Crystals 2018, 8(2), 88; https://doi.org/10.3390/cryst8020088
Received: 19 January 2018 / Revised: 19 January 2018 / Accepted: 31 January 2018 / Published: 6 February 2018
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Abstract
We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe2O4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel
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We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe2O4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel temperature (TN = 240 K) indicates that LuFe2O4+δ shows short-range, two-dimensional (2D) correlations in the FeO5 triangular layers, characterized by the development of a magnetic scattering rod along the 1/3 1/3 L direction, persisting down to 5 K. We also found that on top of the 2D correlations, a long range ferromagnetic component associated with the propagation vector k1 = 0 sets in at around 240 K. On the other hand, an external magnetic field applied along the c-axis effectively favours a three-dimensional (3D) spin correlation between the FeO5 bilayers evidenced by the increase of the intensity of satellite reflections with propagation vector k2 = (1/3, 1/3, 3/2). This magnetic modulation is identical to the charge ordered superstructure, highlighting the field-promoted coupling between the spin and charge degrees of freedom. Formation of the 3D spin correlations suppresses both the rod-type diffuse scattering and the k1 component. Simple symmetry-based arguments provide a natural explanation of the observed phenomenon and put forward a possible charge redistribution in the applied magnetic field. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction
Crystals 2018, 8(2), 89; https://doi.org/10.3390/cryst8020089
Received: 17 January 2018 / Revised: 5 February 2018 / Accepted: 7 February 2018 / Published: 9 February 2018
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Abstract
Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH4] or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions
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Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH4] or [AlH6]3− with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions on Ti-enhanced NaAlH4. In cases wherein alkaline-earth metals (M) are used as a metal cation, MAlH5 with corner-sharing AlH6 octahedron chains are known to form. The crystal structure of SrAlH5 has remained unsolved although two different results have been theoretically and experimentally proposed. Focusing on the corner-sharing AlH6 octahedron chains as a unique feature of the alkaline-earth metal, we here report the crystal structure of SrAlD5 investigated by synchrotron radiation powder X-ray and neutron diffraction. SrAlD5 was elucidated to adopt an orthorhombic unit cell with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4. The Al–D distances (1.77–1.81 Å) in the corner-sharing AlD6 octahedra matched with those in the isolated [AlD6]3− although the D–Al–D angles in the penta-alanates are significantly more distorted than the isolated [AlD6]3−. Full article
(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)
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Open AccessArticle Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures
Crystals 2018, 8(2), 90; https://doi.org/10.3390/cryst8020090
Received: 20 January 2018 / Revised: 6 February 2018 / Accepted: 7 February 2018 / Published: 10 February 2018
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Abstract
The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH
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The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH2, Ni has been added to form Mg2NiH4, which has been mixed with various borohydrides to further tune hydrogen release reactions. De-hydrogenation/re-hydrogenation properties of Mg2NiH4-LiBH4-M(BH4)x (M = Na, K, Mg, Ca) systems have been investigated. Mixtures of borohydrides have been selected to form eutectics, which provide a liquid phase at low temperatures, from 110 °C up to 216 °C. The presence of a liquid borohydride phase decreases the temperature of hydrogen release of Mg2NiH4 but only slight differences have been detected by changing the borohydrides in the eutectic mixture. Full article
(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)
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Open AccessArticle Temperature-Induced Reversible and Irreversible Transitions between Metastable Perovskite Phases in the BiFe1−yScyO3 Solid Solutions
Crystals 2018, 8(2), 91; https://doi.org/10.3390/cryst8020091
Received: 18 January 2018 / Revised: 6 February 2018 / Accepted: 8 February 2018 / Published: 10 February 2018
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Abstract
The antipolar orthorhombic Pnma phase with the 2ap×4ap×22ap superstructure (ap ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO3. Temperature-induced
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The antipolar orthorhombic Pnma phase with the 2 a p × 4 a p × 2 2 a p superstructure (ap ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO3. Temperature-induced structural transformations in metastable perovskite solid solutions with the Pnma structure corresponding to the range of 0.30 ≤ y ≤ 0.60 of the (1−y)BiFeO3-yBiScO3 quasi binary system were studied using temperature X-ray and neutron powder diffraction. These compositions cannot be prepared in bulk form at ambient pressure but can be stabilized in the Pnma phase by means of quenching after synthesis under high pressure. The compositions were investigated in situ between 1.5 K and the temperature of the stability limit of their metastable phases (about 870–920 K). It has been found that heating the as-prepared compositions with the Pnma phase leads to formation of the rhombohedral R3c phase ( 2 a p × 2 a p × 2 3 a p ), which, on cooling down to room temperature, either remains or transforms into a polar orthorhombic Ima2 phase ( 2 a p × 2 a p × 2 a p ). The observed phase transformations in the BiFe1−yScyO3 perovskite series on heating and on cooling are considered in terms of geometrical factors. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Specific Structural Disorder in an Anion Layer and Its Influence on Conducting Properties of New Crystals of the (BEDT-TTF)4A+[M3+(ox)3]G Family, Where G Is 2-Halopyridine; M Is Cr, Ga; A+ Is [K0.8(H3O)0.2]+
Crystals 2018, 8(2), 92; https://doi.org/10.3390/cryst8020092
Received: 24 January 2018 / Revised: 8 February 2018 / Accepted: 8 February 2018 / Published: 10 February 2018
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Abstract
New crystals (14) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A+[M3+(ox)3]3−G}2−, where M is Cr, Ga; G
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New crystals (14) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A+[M3+(ox)3]3−G}2−, where M is Cr, Ga; G is 2-chloropyridine, 2-bromopyridine; and A+ is [K0.8(H3O)0.2]+ have been prepared and their crystal structure and transport properties were studied. All crystals belong to the monoclinic group of the (BEDT-TTF)4A+[M3+(ox)3]G family with β″-packing type of conducting BEDT-TTF layers. In contrast to the known superconducting crystals with M3+ = Fe3+ and G = 2-chloro- or 2-bromopyridine (Tc = 4.0–4.3 K), crystals with Cr3+ and Ga3+ ions exhibit metallic properties down to 0.5 K without superconducting transition. Upon cooling these crystals, the incommensurate superstructure appears, which has never been observed before in the numerous β″-salts of the family. In addition, orthorhombic (sp. group Pbca) semiconducting crystals α″-(BEDT-TTF)5[Ga(ox)3]·3.4·H2O·0.6 EtOH (5) were obtained. It is a new compound in the family of BEDT-TTF crystals with tris(oxalato)metallate anions. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle First-Principles Investigations of the Structural, Anisotropic Mechanical, Thermodynamic and Electronic Properties of the AlNi2Ti Compound
Crystals 2018, 8(2), 93; https://doi.org/10.3390/cryst8020093
Received: 26 December 2017 / Revised: 4 February 2018 / Accepted: 8 February 2018 / Published: 11 February 2018
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Abstract
In this paper, the electronic, mechanical and thermodynamic properties of AlNi2Ti are studied by first-principles calculations in order to reveal the influence of AlNi2Ti as an interfacial phase on ZTA (zirconia toughened alumina)/Fe. The results show that AlNi2
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In this paper, the electronic, mechanical and thermodynamic properties of AlNi2Ti are studied by first-principles calculations in order to reveal the influence of AlNi2Ti as an interfacial phase on ZTA (zirconia toughened alumina)/Fe. The results show that AlNi2Ti has relatively high mechanical properties, which will benefit the impact or wear resistance of the ZTA/Fe composite. The values of bulk, shear and Young’s modulus are 164.2, 63.2 and 168.1 GPa respectively, and the hardness of AlNi2Ti (4.4 GPa) is comparable to common ferrous materials. The intrinsic ductile nature and strong metallic bonding character of AlNi2Ti are confirmed by B/G and Poisson’s ratio. AlNi2Ti shows isotropy bulk modulus and anisotropic elasticity in different crystallographic directions. At room temperature, the linear thermal expansion coefficient (LTEC) of AlNi2Ti estimated by quasi-harmonic approximation (QHA) based on Debye model is 10.6 × 10−6 K−1, close to LTECs of zirconia toughened alumina and iron. Therefore, the thermal matching of ZTA/Fe composite with AlNi2Ti interfacial phase can be improved. Other thermodynamic properties including Debye temperature, sound velocity, thermal conductivity and heat capacity, as well as electronic properties, are also calculated. Full article
(This article belongs to the Special Issue Crystal Structure of Magnetic Materials)
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Open AccessArticle Mg2FeH6 Synthesis Efficiency Map
Crystals 2018, 8(2), 94; https://doi.org/10.3390/cryst8020094
Received: 19 January 2018 / Revised: 5 February 2018 / Accepted: 7 February 2018 / Published: 11 February 2018
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Abstract
The influences of the processing parameters on the Mg2FeH6 synthesis yield were studied. Mixtures of magnesium hydride (MgH2) and iron (Fe) were mechanically milled in a planetary ball mill under argon for 0.5-, 1-, 2- and 3-h periods
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The influences of the processing parameters on the Mg2FeH6 synthesis yield were studied. Mixtures of magnesium hydride (MgH2) and iron (Fe) were mechanically milled in a planetary ball mill under argon for 0.5-, 1-, 2- and 3-h periods and subsequently sintered at temperatures from 300–500 C under hydrogen. The reaction yield, phase content and hydrogen storage properties of the received materials were investigated. The morphologies of the powders after synthesis were studied by SEM. The synthesis effectiveness map was presented. The obtained results prove that synthesis parameters, such as the milling time and synthesis temperature, greatly influence the reaction yield and material properties and show that extended mechanical milling may not be beneficial to the reaction efficiency. Full article
(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)
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Open AccessArticle Ultra-Wide-Bandwidth Tunable Magnetic Fluid-Filled Hybrid Connected Dual-Core Photonic Crystal Fiber Mode Converter
Crystals 2018, 8(2), 95; https://doi.org/10.3390/cryst8020095
Received: 13 January 2018 / Revised: 7 February 2018 / Accepted: 10 February 2018 / Published: 12 February 2018
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Abstract
We propose a tunable magnetic fluid-filled hybrid photonic crystal fiber mode converter. Innovative design principles based on the hybrid connected dual-core photonic crystal fiber and magnetically modulated optical properties of magnetic fluid are developed and numerically verified. The mode converter was designed to
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We propose a tunable magnetic fluid-filled hybrid photonic crystal fiber mode converter. Innovative design principles based on the hybrid connected dual-core photonic crystal fiber and magnetically modulated optical properties of magnetic fluid are developed and numerically verified. The mode converter was designed to convert LP11 in the index-guiding core to the LP01 mode in the photonic bandgap-guiding core. By introducing the magnetic fluid into the air-hole located at the center of the photonic bandgap-guiding core, the mode converter can realize a high coupling efficiency and an ultra-wide bandwidth. The coupling efficiency can reach up to 99.9%. At a fixed fiber length, by adjusting the strength of the magnetic field, the coupling efficiency can reach up to 90% and 95% at wavelengths in the ranges of 1.33 µm–1.85 µm and 1.38 µm–1.75 µm, with bandwidth values reaching 0.52 µm and 0.37 µm, respectively. Moreover, it has a good manufacturing flexibility. The mode converter can be used to implement wideband mode-division multiplexing of few-mode optical fiber for high-capacity telecommunications. Full article
(This article belongs to the Special Issue Photonic Crystal Fiber)
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Open AccessArticle Effects of Alloying Atoms on Antiphase Boundary Energy and Yield Stress Anomaly of L12 Intermetallics: First-Principles Study
Crystals 2018, 8(2), 96; https://doi.org/10.3390/cryst8020096
Received: 4 January 2018 / Revised: 2 February 2018 / Accepted: 2 February 2018 / Published: 12 February 2018
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Abstract
The antiphase boundary energies of {111} and {010} planes in L12 intermetallics (Ni3Ge, Ni3Si, Al3Sc, Ni3Al, Ni3Ga and Al3Ti) under different pressure are presented using first-principle methods. The yield stress
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The antiphase boundary energies of {111} and {010} planes in L1 2 intermetallics (Ni 3 Ge, Ni 3 Si, Al 3 Sc, Ni 3 Al, Ni 3 Ga and Al 3 Ti) under different pressure are presented using first-principle methods. The yield stress anomaly is predicted by the energy criterion p-factor based on the anisotropy of antiphase boundary energies and elasticity. These L1 2 intermetallics exhibit anomalous yield stress behavior except Al 3 Sc. It is found that pressure cannot introduce the transition between anomalous and normal behavior. In order to investigate the transition, Al 3 Sc, Ni 3 Si and Ni 3 Ge with substituting atoms are investigated in detail due to p-factors of them are close to the critical value p c = 3 . Al 3 Sc can change to anomalous when Sc atoms in {010} planes are substituted by Ti with plane concentration 25%. When Li substitutes Al in {111} planes, anomalous Al 3 Sc will change to normal. Ni 3 Si and Ni 3 Ge can exhibit normal yield stress behavior when Ge and Si in {111} planes are substituted by alloying atoms with plane concentrations 12.5% and 25%. When Ga and Al substitute in {010} planes, normal Ni 3 Si and Ni 3 Ge will revert to anomalous behavior. Therefore, transparent transition between normal and anomalous yield stress behavior in L1 2 intermetallics can be introduced by alloying atoms. Full article
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Open AccessArticle Crystal Structure of Shigella flexneri SF173 Reveals a Dimeric Helical Bundle Conformation
Crystals 2018, 8(2), 97; https://doi.org/10.3390/cryst8020097
Received: 29 December 2017 / Revised: 12 February 2018 / Accepted: 12 February 2018 / Published: 14 February 2018
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Abstract
We report the crystal structure and bioinformatic analysis of SF173, a functionally uncharacterized protein from the human enteropathogenic bacteria Shigella flexneri. The structure shows a tightly interlinked dimer formed by adimeric core comprising α2 and α3 helices from both subunits and swapping
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We report the crystal structure and bioinformatic analysis of SF173, a functionally uncharacterized protein from the human enteropathogenic bacteria Shigella flexneri. The structure shows a tightly interlinked dimer formed by adimeric core comprising α2 and α3 helices from both subunits and swapping the N-terminal α1 helix of each monomer. Structural inspection and genomic analysis results suggest that the SF173 might play its putative function by binding to SF172, the partially overlapped upstream product in the operon. As YaeO (an SF172 orthologue) has been identified to be an inhibitor of the bacterial transcription terminator Rho protein, SF173 is suggested to be involved in the regulation of Rho-dependent transcription termination, by inhibiting the Rho protein binding to SF172/YaeO. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle The Electrical Properties of Tb-Doped CaF2 Nanoparticles under High Pressure
Crystals 2018, 8(2), 98; https://doi.org/10.3390/cryst8020098
Received: 9 January 2018 / Revised: 11 February 2018 / Accepted: 12 February 2018 / Published: 15 February 2018
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Abstract
The high-pressure transport behavior of CaF2 nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca2+ by Tb
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The high-pressure transport behavior of CaF2 nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca2+ by Tb3+ leads to deformation in the lattice, and finally lowers the transition pressure. The F ions diffusion, electronic transport, and charge-discharge process become more difficult with the rising pressure. In the electronic transport process, defects at grains play a dominant role. The charge carriers include both F ions and electrons, and electrons are dominant in the transport process. The Tb doping improves the pressure effect on the transport behavior of CaF2 nanocrystals. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Atomic Charges and Chemical Bonding in Y-Ga Compounds
Crystals 2018, 8(2), 99; https://doi.org/10.3390/cryst8020099
Received: 25 January 2018 / Revised: 13 February 2018 / Accepted: 14 February 2018 / Published: 16 February 2018
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Abstract
A negative deviation from Vegard rule for the average atomic volume versus yttrium content was found from experimental crystallographic information about the binary compounds of yttrium with gallium. Analysis of the electron density (DFT calculations) employing the quantum theory of atoms in molecules
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A negative deviation from Vegard rule for the average atomic volume versus yttrium content was found from experimental crystallographic information about the binary compounds of yttrium with gallium. Analysis of the electron density (DFT calculations) employing the quantum theory of atoms in molecules revealed an increase in the atomic volumes of both Y and Ga with the increase in yttrium content. The non-linear increase is caused by the strengthening of covalent Y-Ga interactions with stronger participation of genuine penultimate shell electrons (4d electrons of yttrium) in the valence region. Summing the calculated individual atomic volumes for a unit cell allows understanding of the experimental trend. With increasing yttrium content, the polarity of the Y-Ga bonding and, thus its ionicity, rises. The covalency of the atomic interactions in Y-Ga compounds is consistent with their delocalization from two-center to multi-center ones. Full article
(This article belongs to the Special Issue Experimental and Theoretical Electron Density Analysis of Crystals)
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Open AccessArticle Incorporation of Hexanuclear Mn(II,III) Carboxylate Clusters with a {Mn6O2} Core in Polymeric Structures
Crystals 2018, 8(2), 100; https://doi.org/10.3390/cryst8020100
Received: 11 January 2018 / Revised: 12 February 2018 / Accepted: 15 February 2018 / Published: 17 February 2018
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Abstract
A new series of hexanuclear mixed-valent carboxylate coordination clusters of the type [Mn6O2(O2CR)10L4] (R = CMe3; CHMe2) featuring a {MnII4MnIII2(μ4-O)2} core of composition [Mn6O2(O2CCMe3)10(Me3CCO2H)3(EtOH)]•(Me3CCO2H) (1), [Mn6O2(O2CCMe3)10(Me3CCO2H)2 (EtOH)2]•2(EtOH) (2) and [Mn6O2(O2CCMe3)10(Me3CCO2H)2(MeOH)2]•2(MeOH)•H2O (3), and coordination polymers which incorporate such clusters, namely [Mn6O2(O2CCHMe2)10(pyz)(MeOH)2]n (4), {[Mn6O2(O2CCHMe2)10(pyz)1.5(H2O)]•0.5(H2O)}n (5),
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A new series of hexanuclear mixed-valent carboxylate coordination clusters of the type [Mn6O2(O2CR)10L4] (R = CMe3; CHMe2) featuring a {MnII4MnIII2(μ4-O)2} core of composition [Mn6O2(O2CCMe3)10(Me3CCO2H)3(EtOH)]•(Me3CCO2H) (1), [Mn6O2(O2CCMe3)10(Me3CCO2H)2 (EtOH)2]•2(EtOH) (2) and [Mn6O2(O2CCMe3)10(Me3CCO2H)2(MeOH)2]•2(MeOH)•H2O (3), and coordination polymers which incorporate such clusters, namely [Mn6O2(O2CCHMe2)10(pyz)(MeOH)2]n (4), {[Mn6O2(O2CCHMe2)10(pyz)1.5(H2O)]•0.5(H2O)}n (5), and [Mn6O2(O2CCMe3)10(HO2CCMe3)2(en)]n (6), have been synthesized (where pyz = pyrazine, en = ethyl nicotinate). The modification of the cluster surface by a diverse combination of capped or bridging ligands attached to peripheral MnII atoms results in discrete clusters with a closed hydrophobic exterior shell in 1 and 2, supramolecular chains built through hydrogen bonded solvent molecule clusters in 3, linear coordination polymers in 4 and 6 or a ladder-like coordination polymer in 5. The H-bonded coordination polymers 4 and 5 form supramolecular layers in crystals. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Atomic-Site-Specific Analysis on Out-of-Plane Elasticity of Convexly Curved Graphene and Its Relationship to s p 2 to s p 3 Re-Hybridization
Crystals 2018, 8(2), 102; https://doi.org/10.3390/cryst8020102
Received: 15 January 2018 / Revised: 12 February 2018 / Accepted: 12 February 2018 / Published: 20 February 2018
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Abstract
The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties
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The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties of graphene under compressing and stretching deformations have been exclusively investigated by local-probe techniques. Here we report that the interatomic attractive force introduced by atomic force microscopy triggers “single”-atom displacement and consequently enables us to determine out-of-plane elasticities of convexly curved graphene including its atomic-site-specific variation. We have quantitatively evaluated the relationship between the out-of-plane displacement and elasticity of convexly curved graphene by three-dimensional force field spectroscopy on a side-wall of a hollow tube with a well-defined curvature. The substantially small intrinsic modulus that complies with continuum mechanics has been found to increase significantly at atomically specific locations, where s p 2 to s p 3 re-hybridization would certainly take place. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessFeature PaperArticle Synthesis, Crystal Structure Analysis and Decomposition of RbAlH4
Crystals 2018, 8(2), 103; https://doi.org/10.3390/cryst8020103
Received: 31 January 2018 / Revised: 16 February 2018 / Accepted: 21 February 2018 / Published: 22 February 2018
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Abstract
RbAlH4, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The
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RbAlH4, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The structure refinement of neutron diffraction data confirms that RbAlD4 is isostructural to KAlD4. The decomposition proceeds via two distinct processes at temperatures above 275 °C. However, the structures formed during decomposition seem to be different from the compounds formed during hydrogen release of early alkali metal aluminum hydrides. Full article
(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)
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Open AccessArticle One Step Preparation of Fe–FeO–Graphene Nanocomposite through Pulsed Wire Discharge
Crystals 2018, 8(2), 104; https://doi.org/10.3390/cryst8020104
Received: 31 January 2018 / Revised: 14 February 2018 / Accepted: 14 February 2018 / Published: 23 February 2018
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Abstract
The Fe–FeO–graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded
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The Fe–FeO–graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded to analyze the process of the pulsed wire discharge. The as-prepared samples—under different charging voltages—were recovered and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM). Curved and loose graphene films that were anchored with spherical Fe and FeO nanoparticles were obtained at the charging voltage of 8–10 kV. The present study discusses the mechanism by which the Fe–FeO–graphene nanocomposite material was formed during the pulsed wire discharge process. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle Mechanically Robust 3D Graphene–Hydroxyapatite Hybrid Bioscaffolds with Enhanced Osteoconductive and Biocompatible Performance
Crystals 2018, 8(2), 105; https://doi.org/10.3390/cryst8020105
Received: 30 January 2018 / Revised: 16 February 2018 / Accepted: 21 February 2018 / Published: 23 February 2018
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Abstract
In this paper, we describe three-dimensional (3D) hierarchical graphene–hydroxyapatite hybrid bioscaffolds (GHBs) with a calcium phosphate salt electrochemically deposited onto the framework of graphene foam (GF). The morphology of the hydroxyapatite (HA) coverage over GF was controlled by the deposition conditions, including temperature
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In this paper, we describe three-dimensional (3D) hierarchical graphene–hydroxyapatite hybrid bioscaffolds (GHBs) with a calcium phosphate salt electrochemically deposited onto the framework of graphene foam (GF). The morphology of the hydroxyapatite (HA) coverage over GF was controlled by the deposition conditions, including temperature and voltage. The HA obtained at the higher temperature demonstrates the more uniformly distributed crystal grain with the smaller size. The as-prepared GHBs show a high elasticity with recoverable compressive strain up to 80%, and significantly enhanced strength with Young’s modulus up to 0.933 MPa compared with that of pure GF template (~7.5 kPa). Moreover, co-culture with MC3T3-E1 cells reveals that the GHBs can more effectively promote the proliferation of MC3T3-E1 osteoblasts with good biocompatibility than pure GF and the control group. The superior performance of GHBs suggests their promising applications as multifunctional materials for the repair and regeneration of bone defects. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessCommunication Synthesis and Fluorescence Properties of Asymmetrical Salamo-Type Tetranuclear Zinc(II) Complex
Crystals 2018, 8(2), 107; https://doi.org/10.3390/cryst8020107
Received: 25 January 2018 / Revised: 19 February 2018 / Accepted: 22 February 2018 / Published: 24 February 2018
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Abstract
A new tetranuclear zinc(II) complex with an asymmetrical Salamo-type chelating ligand, H3L (5-methoxy-6′-hydroxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), was synthesized and characterized using FT-IR, elemental analyses, X-ray single crystal diffraction method, UV-Vis, and fluorescence spectra. The zinc(II) complex possesses the cell parameters a = 8.1960(7) Å,
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A new tetranuclear zinc(II) complex with an asymmetrical Salamo-type chelating ligand, H3L (5-methoxy-6′-hydroxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), was synthesized and characterized using FT-IR, elemental analyses, X-ray single crystal diffraction method, UV-Vis, and fluorescence spectra. The zinc(II) complex possesses the cell parameters a = 8.1960(7) Å, b = 9.8127(8) Å, c = 16.5428(15) Å, Z = 1, V = 1172.5(2) Å3, R1 = 0.0722, and wR2 = 0.1558, and crystallizes in the triclinic system, with space group P-1. X-ray crystal structure analysis reveals that Zn1 and Zn2 atoms are all pentacoordinated and adopt slightly twisted tetragonal pyramidal and trigonal bipyramidal geometries. The zinc(II) complex forms a 1D supramolecular chain via intermolecular hydrogen bonds along the b axis. Besides, the fluorescence properties have been discussed. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Review

Jump to: Editorial, Research

Open AccessReview Characterization of Pb-Free KNbO3- and (Na,Bi)TiO3-Based Piezoelectric Single-Crystals Using X-ray and Neutron Diffraction
Crystals 2018, 8(2), 49; https://doi.org/10.3390/cryst8020049
Received: 19 December 2017 / Revised: 9 January 2018 / Accepted: 10 January 2018 / Published: 23 January 2018
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Abstract
In view of serious environmental concerns with traditional Pb-based piezoelectrics, the search for new Pb-free alternatives has intensified recently. A thorough investigation of structure-property relationships in Pb-free piezoelectrics is desired in order to design new material compositions with high electromechanical properties that can
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In view of serious environmental concerns with traditional Pb-based piezoelectrics, the search for new Pb-free alternatives has intensified recently. A thorough investigation of structure-property relationships in Pb-free piezoelectrics is desired in order to design new material compositions with high electromechanical properties that can be operated over a broader range of conditions. Recent availability of high-quality single crystals has not only opened the possibility for achieving multifold enhancements in the electromechanical properties in this new class of materials, but has also provided opportunities to undertake fundamental studies on their structure-property relationships. In the following pages, I review some of the recent X-ray and neutron diffraction studies of Pb-free piezoelectric single crystals, which have provided novel insights into their multiscale stimuli-induced structural mechanisms, including phase transitions, nanoscale structural ordering, lattice instability, and domain re-orientation. Opportunities and challenges for future progress in this area of study are discussed. Full article
(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)
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Open AccessReview Rare-Earth Tantalates and Niobates Single Crystals: Promising Scintillators and Laser Materials
Crystals 2018, 8(2), 55; https://doi.org/10.3390/cryst8020055
Received: 11 December 2017 / Revised: 26 December 2017 / Accepted: 28 December 2017 / Published: 24 January 2018
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Abstract
Rare-earth tantalates, with high density and monoclinic structure, and niobates with monoclinic structure have been paid great attention as potential optical materials. In the last decade, we focused on the crystal growth technology of rare-earth tantalates and niobates and studied their luminescence and
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Rare-earth tantalates, with high density and monoclinic structure, and niobates with monoclinic structure have been paid great attention as potential optical materials. In the last decade, we focused on the crystal growth technology of rare-earth tantalates and niobates and studied their luminescence and physical properties. A series of rare-earth tantalates and niobates crystals have been grown by the Czochralski method successfully. In this work, we summarize the research results on the crystal growth, scintillation, and laser properties of them, including the absorption and emission spectra, spectral parameters, energy levels structure, and so on. Most of the tantalates and niobates exhibit excellent luminescent properties, rich physical properties, and good chemical stability, indicating that they are potential outstanding scintillators and laser materials. Full article
(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)
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Open AccessReview Recent Achievements on Photovoltaic Optoelectronic Tweezers Based on Lithium Niobate
Crystals 2018, 8(2), 65; https://doi.org/10.3390/cryst8020065
Received: 22 December 2017 / Revised: 22 January 2018 / Accepted: 24 January 2018 / Published: 30 January 2018
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Abstract
This review presents an up-dated summary of the fundamentals and applications of optoelectronic photovoltaic tweezers for trapping and manipulation of nano-objects on the surface of lithium niobate crystals. It extends the contents of previous reviews to cover new topics and developments which have
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This review presents an up-dated summary of the fundamentals and applications of optoelectronic photovoltaic tweezers for trapping and manipulation of nano-objects on the surface of lithium niobate crystals. It extends the contents of previous reviews to cover new topics and developments which have emerged in recent years and are marking the trends for future research. Regarding the theoretical description of photovoltaic tweezers, detailed simulations of the electrophoretic and dielectrophoretic forces acting on different crystal configurations are discussed in relation to the structure of the obtained trapping patterns. As for the experimental work, we will pay attention to the manipulation and patterning of micro-and nanoparticles that has experimented an outstanding progress and relevant applications have been reported. An additional focus is now laid on recent work about micro-droplets, which is a central topic in microfluidics and optofluidics. New developments in biology and biomedicine also constitute a relevant part of the review. Finally, some topics partially related with photovoltaic tweezers and a discussion on future prospects and challenges are included. Full article
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Open AccessReview Vertical Transistors Based on 2D Materials: Status and Prospects
Crystals 2018, 8(2), 70; https://doi.org/10.3390/cryst8020070
Received: 15 December 2017 / Revised: 21 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
Two-dimensional (2D) materials, such as graphene (Gr), transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN), offer interesting opportunities for the implementation of vertical transistors for digital and high-frequency electronics. This paper reviews recent developments in this field, presenting the main vertical device
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Two-dimensional (2D) materials, such as graphene (Gr), transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN), offer interesting opportunities for the implementation of vertical transistors for digital and high-frequency electronics. This paper reviews recent developments in this field, presenting the main vertical device architectures based on 2D/2D or 2D/3D material heterostructures proposed so far. For each of them, the working principles and the targeted application field are discussed. In particular, tunneling field effect transistors (TFETs) for beyond-CMOS low power digital applications are presented, including resonant tunneling transistors based on Gr/h-BN/Gr stacks and band-to-band tunneling transistors based on heterojunctions of different semiconductor layered materials. Furthermore, recent experimental work on the implementation of the hot electron transistor (HET) with the Gr base is reviewed, due to the predicted potential of this device for ultra-high frequency operation in the THz range. Finally, the material sciences issues and the open challenges for the realization of 2D material-based vertical transistors at a large scale for future industrial applications are discussed. Full article
(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)
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Open AccessReview A Brief Review of the Effects of Pressure on Wolframite-Type Oxides
Crystals 2018, 8(2), 71; https://doi.org/10.3390/cryst8020071
Received: 8 January 2018 / Revised: 28 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
In this article, we review the advances that have been made on the understanding of the high-pressure (HP) structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but
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In this article, we review the advances that have been made on the understanding of the high-pressure (HP) structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but also tantalates and niobates, with an isomorphic ambient-pressure wolframite structure, have been included in this review. Apart from estimating the bulk moduli of all known wolframites, the cation–oxygen bond distances and their change with pressure have been correlated with their compressibility. The composition variations of all wolframites have been employed to understand their different structural phase transitions to post-wolframite structures as a response to high pressure. The number of Raman modes and the changes in the band-gap energy have also been analyzed in the basis of these compositional differences. The reviewed results are relevant for both fundamental science and for the development of wolframites as scintillating detectors. The possible next research avenues of wolframites under compression have also been evaluated. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessReview Enhancing Light Extraction of Inorganic Scintillators Using Photonic Crystals
Crystals 2018, 8(2), 78; https://doi.org/10.3390/cryst8020078
Received: 30 November 2017 / Revised: 25 December 2017 / Accepted: 27 December 2017 / Published: 1 February 2018
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Abstract
Inorganic scintillators are commonly used as sensors for ionizing radiation detectors in a variety of applications, ranging from particle and nuclear physics detectors, medical imaging, nuclear installations radiation control, homeland security, well oil logging and a number of industrial non-destructive investigations. For all
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Inorganic scintillators are commonly used as sensors for ionizing radiation detectors in a variety of applications, ranging from particle and nuclear physics detectors, medical imaging, nuclear installations radiation control, homeland security, well oil logging and a number of industrial non-destructive investigations. For all these applications, the scintillation light produced by the energy deposited in the scintillator allows the determination of the position, the energy and the time of the event. However, the performance of these detectors is often limited by the amount of light collected on the photodetector. A major limitation comes from the fact that inorganic scintillators are generally characterized by a high refractive index, as a consequence of the required high density to provide the necessary stopping power for ionizing radiation. The index mismatch between the crystal and the surrounding medium (air or optical grease) strongly limits the light extraction efficiency because of total internal reflection (TIR), increasing the travel path and the absorption probability through multiple bouncings of the photons in the crystal. Photonic crystals can overcome this problem and produce a controllable index matching between the crystal and the output medium through an interface made of a thin nano-structured layer of optically-transparent high index material. This review presents a summary of the works aiming at improving the light collection efficiency of scintillators using photonic crystals since this idea was introduced 10 years ago. Full article
(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)
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Open AccessReview Revealing Tendencies in the Electronic Structures of Polar Intermetallic Compounds
Crystals 2018, 8(2), 80; https://doi.org/10.3390/cryst8020080
Received: 13 January 2018 / Revised: 27 January 2018 / Accepted: 29 January 2018 / Published: 2 February 2018
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Abstract
The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by
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The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by Zintl and Hume–Rothery help to understand and forecast the bonding motifs in several intermetallic compounds, there is an emerging group of compounds dubbed as polar intermetallic phases whose electronic structures cannot be categorized by the aforementioned conceptions. These polar intermetallic compounds can be divided into two categories based on the building units in their crystal structures and the expected charge distributions between their components. On the one hand, there are polar intermetallic compounds composed of polycationic clusters surrounded by anionic ligands, while, on the other hand, the crystal structures of other polar intermetallic compounds comprise polyanionic units combined with monoatomic cations. In this review, we present the quantum chemical techniques to gain access to the electronic structures of polar intermetallic compounds, evaluate certain trends from a survey of the electronic structures of diverse polar intermetallic compounds, and show options based on quantum chemical approaches to predict the properties of such materials. Full article
(This article belongs to the Special Issue Functional Multi-Scale Crystals)
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Open AccessReview Multifunctional Aromatic Carboxylic Acids as Versatile Building Blocks for Hydrothermal Design of Coordination Polymers
Crystals 2018, 8(2), 83; https://doi.org/10.3390/cryst8020083
Received: 15 January 2018 / Revised: 28 January 2018 / Accepted: 29 January 2018 / Published: 3 February 2018
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Abstract
Selected recent examples of coordination polymers (CPs) or metal-organic frameworks (MOFs) constructed from different multifunctional carboxylic acids with phenyl-pyridine or biphenyl cores have been discussed. Despite being still little explored in crystal engineering research, such types of semi-rigid, thermally stable, multifunctional and versatile
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Selected recent examples of coordination polymers (CPs) or metal-organic frameworks (MOFs) constructed from different multifunctional carboxylic acids with phenyl-pyridine or biphenyl cores have been discussed. Despite being still little explored in crystal engineering research, such types of semi-rigid, thermally stable, multifunctional and versatile carboxylic acid building blocks have become very promising toward the hydrothermal synthesis of metal-organic architectures possessing distinct structural features, topologies, and functional properties. Thus, the main aim of this mini-review has been to motivate further research toward the synthesis and application of coordination polymers assembled from polycarboxylic acids with phenyl-pyridine or biphenyl cores. The importance of different reaction parameters and hydrothermal conditions on the generation and structural types of CPs or MOFs has also been highlighted. The influence of the type of main di- or tricarboxylate ligand, nature of metal node, stoichiometry and molar ratio of reagents, temperature, and presence of auxiliary ligands or templates has been showcased. Selected examples of highly porous or luminescent CPs, compounds with unusual magnetic properties, and frameworks for selective sensing applications have been described. Full article
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