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Crystals, Volume 8, Issue 5 (May 2018)

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Cover Story (view full-size image) k-(BEDT-TTF)2X (X= Cu[N(CN)2]Cl, Cu2(CN)3, and Ag2(CN)3) are known as Mott insulators driven by [...] Read more.
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Open AccessArticle Spatially Nonuniform Superconductivity in Quasi-Two-Dimensional Organic Charge-Transfer Salts
Crystals 2018, 8(5), 183; https://doi.org/10.3390/cryst8050183
Received: 14 February 2018 / Revised: 19 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
In the following, a brief overview on the recently found robust experimental evidence for the existence of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state in layered organic superconductors is given. These electronically quasi-two-dimensional (2D) clean-limit superconductors are ideally suited for observing FFLO states. Applying a magnetic
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In the following, a brief overview on the recently found robust experimental evidence for the existence of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state in layered organic superconductors is given. These electronically quasi-two-dimensional (2D) clean-limit superconductors are ideally suited for observing FFLO states. Applying a magnetic field parallel to the layers suppresses orbital effects and superconductivity is observed beyond the Pauli paramagnetic limit. Both, thermodynamic as well as microscopic experimental data show the existence of an additional high-field low-temperature superconducting state having a one-dimensionally modulated order parameter. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle P-T Phase Diagram of LuFe2O4
Crystals 2018, 8(5), 184; https://doi.org/10.3390/cryst8050184
Received: 7 March 2018 / Revised: 17 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
The high-pressure behavior of LuFe2O4 is characterized based on synchrotron X-ray diffraction and neutron diffraction, resistivity measurements, X-ray absorption spectroscopy and infrared spectroscopy studies. The results obtained enabled us to propose a P-T phase diagram. In this study,
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The high-pressure behavior of LuFe2O4 is characterized based on synchrotron X-ray diffraction and neutron diffraction, resistivity measurements, X-ray absorption spectroscopy and infrared spectroscopy studies. The results obtained enabled us to propose a P-T phase diagram. In this study, the low pressure charge-ordering melting could be detected by synchrotron XRD in the P-T space. In addition to the ambient pressure monoclinic C2/m and rhombohedral R 3 ¯ m phases, the possible P 1 ¯ triclinic phase, the monoclinic high pressure form Pm and metastable modulated monoclinic phases were observed; the latter modulated monoclinic phases were not observed in the present neutron diffraction data. Furthermore, the transition to the Pm phase which was already characterized by strong kinetics is found to be favored at high temperature (373 K). Based on X-ray absorption spectroscopy data the Pm phase, which could be recovered at atmospheric pressure, can be explained by a change in the Fe-local environment from a five-fold coordination to a distorted 5 + 1 one. Full article
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Open AccessArticle Effects of Iodine Doping on Carrier Behavior at the Interface of Perovskite Crystals: Efficiency and Stability
Crystals 2018, 8(5), 185; https://doi.org/10.3390/cryst8050185
Received: 22 March 2018 / Revised: 21 April 2018 / Accepted: 21 April 2018 / Published: 25 April 2018
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Abstract
The interface related to the polycrystalline hybrid perovskite thin film plays an essential role in the resulting device performance. Iodine was employed as an additive to modify the interface between perovskite and spiro-OMeTAD hole transport layer. The oxidation ability of iodine significantly improved
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The interface related to the polycrystalline hybrid perovskite thin film plays an essential role in the resulting device performance. Iodine was employed as an additive to modify the interface between perovskite and spiro-OMeTAD hole transport layer. The oxidation ability of iodine significantly improved the efficiency of charge extraction for perovskite solar cells. It reveals that the Open Circuit Voltage (Voc) and Fill Factor (FF) of perovskite solar cells were improved substantially due to the dopant, which is mainly attributed to the interfacial improvement. It was found that the best efficiency of the devices was achieved when the dopant of iodine was in equivalent mole concentration with that of spiro-OMeTAD. Moreover, the long-term stability of the corresponding device was investigated. Full article
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Open AccessArticle Rhombohedral Distortion of the Cubic MgCu2-Type Structure in Ca2Pt3Ga and Ca2Pd3Ga
Crystals 2018, 8(5), 186; https://doi.org/10.3390/cryst8050186
Received: 27 March 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
Two new fully ordered ternary Laves phase compounds, Ca2Pt3Ga and Ca2Pd3Ga, have been synthesized and characterized by powder and single-crystal X-ray diffraction along with electronic structure calculations. Ca2Pd3Ga was synthesized as
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Two new fully ordered ternary Laves phase compounds, Ca2Pt3Ga and Ca2Pd3Ga, have been synthesized and characterized by powder and single-crystal X-ray diffraction along with electronic structure calculations. Ca2Pd3Ga was synthesized as a pure phase whereas Ca2Pt3Ga was found as a diphasic product with Ca2Pt2Ga. Electronic structure calculations were performed to try and understand why CaPt2 and CaPd2, which crystalize in the cubic MgCu2-type Laves phase structure, distort to the ordered rhombohedral variant, first observed in the magneto-restricted TbFe2 compound, with the substitution of twenty-five percent of the Pt/Pd with Ga. Electronic stability was investigated by changing the valence electron count from 22e/f.u. in CaPd2 and CaPt2 (2x) to 37e/f.u. in Ca2Pd3Ga and Ca2Pt3Ga, which causes the Fermi level to shift to a more energetically favorable location in the DOS. The coloring problem was studied by placing a single Ga atom in each of four tetrahedra of the cubic unit cell of the MgCu2-type structure, with nine symmetrically inequivalent models being investigated. Non-optimized and optimized total energy analyses of structural characteristics, along with electronic properties, will be discussed. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Sc2[Se2O5]3: The First Rare-Earth Metal Oxoselenate(IV) with Exclusively [Se2O5]2− Anions
Crystals 2018, 8(5), 187; https://doi.org/10.3390/cryst8050187
Received: 23 March 2018 / Revised: 20 April 2018 / Accepted: 20 April 2018 / Published: 26 April 2018
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Abstract
The scandium oxodiselenate(IV) Sc2[Se2O5]3 was synthesized via solid-state reactions between scandium sesquioxide (Sc2O3) and selenium dioxide (SeO2) with thallium(I) chloride (TlCl) as fluxing agent in molar ratios of 1:4:2. Evacuated
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The scandium oxodiselenate(IV) Sc2[Se2O5]3 was synthesized via solid-state reactions between scandium sesquioxide (Sc2O3) and selenium dioxide (SeO2) with thallium(I) chloride (TlCl) as fluxing agent in molar ratios of 1:4:2. Evacuated fused silica ampoules were used as reactions vessels for annealing the mixtures for five days at 800 °C. The new scandium compound crystallizes in the triclinic space group P 1 ¯ with the lattice parameters a = 663.71(5) pm, b = 1024.32(7) pm, c = 1057.49(8) pm, α = 81.034(2)°, β = 87.468(2)°, γ = 89.237(2)° and Z = 2. There are two distinct Sc3+ positions, which show six-fold coordination by oxygen atoms as [ScO6]9− octahedra (d(Sc–O) = 205–212 pm). Three different [Se2O5]2− anions provide these oxygen atoms with their terminal ligands (Ot). Each of the six selenium(IV) central atoms exhibit a stereochemically active lone pair of electrons, so that all [Se2O5]2− anions consist of two ψ1-tetrahedral [SeO3]2− subunits (d(Se–Ot) = 164–167 pm, d(Se–Ob) = 176–185 pm, ∢(O–Se–O) = 93–104°) sharing one bridging oxygen atom (Ob) with ∢(Se–Ob–Se) = 121–128°. The vibrational modes of the complex anionic [Se2O5]2− entities were characterized via single-crystal Raman spectroscopy. Full article
(This article belongs to the Special Issue Crystal Structures of Compounds Containing Ions Selenite)
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Open AccessArticle Comparative Study on the Sand Bioconsolidation through Calcium Carbonate Precipitation by Sporosarcina pasteurii and Bacillus subtilis
Crystals 2018, 8(5), 189; https://doi.org/10.3390/cryst8050189
Received: 11 November 2017 / Revised: 20 March 2018 / Accepted: 21 April 2018 / Published: 27 April 2018
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Abstract
To investigate potential implications of microbial activity on sand bioconsolidation and subsurface environments, two ureolytic strains, Sporosarcina pasteurii and Bacillus subtilis were tested for the production of calcium carbonate (CaCO3). Laboratory experiments with monoculture S. pasteurii (column 1) and coculture S.
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To investigate potential implications of microbial activity on sand bioconsolidation and subsurface environments, two ureolytic strains, Sporosarcina pasteurii and Bacillus subtilis were tested for the production of calcium carbonate (CaCO3). Laboratory experiments with monoculture S. pasteurii (column 1) and coculture S. pasteurii-B. subtilis (column 2) were conducted to determine urea and calcium chloride reactivity and volumetric carbonate formation. Both columns were able to consolidate sand, whereas, column 1 induced greater CaCO3 precipitation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed two columns with different mineralogy with calcite, and vaterite formation. Column 1 showed rhombohedral and trigonal crystals morphology, whereas column 2 developed the prismatic calcite and the spherulite vaterite crystals might be due to the differences of the micro-environment caused by the urease expression of these bacterial species. These results indicate the possibility of using those crystals to cement loose sand whereas, highlighted the importance of combining these techniques to understand the geomicrobiology found in the subsurface environments. Full article
(This article belongs to the Special Issue Carbonates)
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Open AccessArticle Electrodynamics in Organic Dimer Insulators Close to Mott Critical Point
Crystals 2018, 8(5), 190; https://doi.org/10.3390/cryst8050190
Received: 26 March 2018 / Revised: 18 April 2018 / Accepted: 18 April 2018 / Published: 27 April 2018
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Abstract
Organic layered charge-transfer salts κ -(BEDT-TTF) 2X form highly frustrated lattices of molecular dimers in which strong correlations give rise to Mott insulating states situated close to the metal-to-insulator phase boundary. The salts κ -(BEDT-TTF) 2 Cu 2 (CN) 3 and κ
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Organic layered charge-transfer salts κ -(BEDT-TTF) 2 X form highly frustrated lattices of molecular dimers in which strong correlations give rise to Mott insulating states situated close to the metal-to-insulator phase boundary. The salts κ -(BEDT-TTF) 2 Cu 2 (CN) 3 and κ -(BEDT-TTF) 2 Ag 2 (CN) 3 have been considered as prime candidates for a quantum spin liquid, while κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl has been suggested as a prototypical charge-order-driven antiferromagnet. In this paper, we summarize and discuss several key results, including some not reported previously, obtained in search to clarify the competition of these two ground states. The origin of anomalous dielectric response found at low temperatures in all three salts is also discussed. We conclude by pointing out the relevant new insights into the role of frustration and random disorder in the suppression of magnetic ordering and formation of the spin liquid state. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle Analysis of Waveguides on Lithium Niobate Thin Films
Crystals 2018, 8(5), 191; https://doi.org/10.3390/cryst8050191
Received: 5 April 2018 / Revised: 24 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
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Abstract
Waveguides formed by etching, proton-exchange (PE), and strip-loaded on single-crystal lithium niobate (LN) thin film were designed and simulated by a full-vectorial finite difference method. The single-mode condition, optical power distribution, and bending loss of these kinds of waveguides were studied and compared
[...] Read more.
Waveguides formed by etching, proton-exchange (PE), and strip-loaded on single-crystal lithium niobate (LN) thin film were designed and simulated by a full-vectorial finite difference method. The single-mode condition, optical power distribution, and bending loss of these kinds of waveguides were studied and compared systematically. For the PE waveguide, the optical power distributed in LN layer had negligible change with the increase of PE thickness. For the strip-loaded waveguide, the relationships between optical power distribution in LN layer and waveguide thickness were different for quasi-TE (q-TE) and quasi-TM (q-TM) modes. The bending loss would decrease with the increase of bending radius. There was a bending loss caused by the electromagnetic field leakage when the neff of q-TM waveguide was smaller than that of nearby TE planar waveguide. LN ridge waveguides possessed a low bending loss even at a relatively small bending radius. This study is helpful for the understanding of waveguide structures as well as for the optimization and the fabrication of high-density integrated optical components. Full article
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Open AccessArticle Ex-Situ Thermal Treatment Effects on the Temperature Dependent Carriers Dynamics in InAs/InGaAs/GaAs Quantum Dots
Crystals 2018, 8(5), 192; https://doi.org/10.3390/cryst8050192
Received: 10 March 2018 / Revised: 18 April 2018 / Accepted: 26 April 2018 / Published: 28 April 2018
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Abstract
The effects of post-growth thermal annealing of InAs QD with the high in-content strain reducing layer (SRL) on the temperature dependent PL properties have been investigated. The as-grown QD have shown an atypical behavior manifested by a sigmoidal emission energy and V-shaped linewidth
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The effects of post-growth thermal annealing of InAs QD with the high in-content strain reducing layer (SRL) on the temperature dependent PL properties have been investigated. The as-grown QD have shown an atypical behavior manifested by a sigmoidal emission energy and V-shaped linewidth evolution with temperature. These behaviors have been progressively glossed by subjecting the structure to post growth annealing at 650 °C and 750 °C for 50 s. The results are discussed in the frame of the localized states ensemble model, which reveals that carriers transfer take place by thermal activation to the continuum states of the strain-reducing layer and subsequent redistribution. Full article
(This article belongs to the Special Issue Crystal Growth Methods for Quantum Materials)
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Open AccessArticle Se–Cl Interactions in Selenite Chlorides: A Theoretical Study
Crystals 2018, 8(5), 193; https://doi.org/10.3390/cryst8050193
Received: 29 March 2018 / Revised: 24 April 2018 / Accepted: 25 April 2018 / Published: 29 April 2018
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Abstract
The Se–Cl interactions in five selenite chlorides (α,β-Zn2(SeO3)Cl2 (sofiite and its polymorph), α,β-Cu5O2(SeO3)2Cl2 (georgbokiite and parageorgbokiite), and KCdCu7O2(SeO3)2Cl9 (burnsite)) have
[...] Read more.
The Se–Cl interactions in five selenite chlorides (α,β-Zn2(SeO3)Cl2 (sofiite and its polymorph), α,β-Cu5O2(SeO3)2Cl2 (georgbokiite and parageorgbokiite), and KCdCu7O2(SeO3)2Cl9 (burnsite)) have been investigated by means of the analysis of their theoretical electron density distributions. The analysis reveals the existence in the structures of two basic types of interactions: intermediate interactions with essential covalent contribution and closed-shell interactions. In Zn2(SeO3)Cl2 polymorphs and burnsite, all metal-oxide and metal-chloride interactions are of the first type, whereas in georgbokiite and parageorgbokiite, the Jahn–Teller distortion results in the elongation of some of the Cu–X bonds and their transition to the closed-shell type. All anion–anion interactions are of the closed-shell type. The energy of the closed-shell Se–Cl interactions can be estimated as 1.4–2.6 kcal.mol−1, which is comparable to weak hydrogen bonds. Despite their weakness, these interactions provide additional stabilization of structural architectures. The Se4+–Cl configurations are localized inside framework channels or cavities, which can be therefore be viewed as regions of weak and soft interactions in the structure. Full article
(This article belongs to the Special Issue Crystal Structures of Compounds Containing Ions Selenite)
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Open AccessArticle Lattice Correspondence and Growth Structures of Monoclinic Mg4Zn7 Phase Growing on an Icosahedral Quasicrystal
Crystals 2018, 8(5), 194; https://doi.org/10.3390/cryst8050194
Received: 11 April 2018 / Revised: 26 April 2018 / Accepted: 27 April 2018 / Published: 1 May 2018
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Abstract
Mg4Zn7 phase, with a monoclinic unit cell, a layered structure and a unique axis showing pseudo-tenfold symmetry, grows over icosahedral quasicrystalline phase in a manner similar to a decagonal quasicrystal. In this study, the relationship of this phase to icosahedral
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Mg 4 Zn 7 phase, with a monoclinic unit cell, a layered structure and a unique axis showing pseudo-tenfold symmetry, grows over icosahedral quasicrystalline phase in a manner similar to a decagonal quasicrystal. In this study, the relationship of this phase to icosahedral quasicrystal is brought out by a transmission electron microscopy study of Mg 4 Zn 7 phase growing on icosahedral phase in a cast Mg-Zn-Y alloy. Lattice correspondences between the two phases have been determined by electron diffraction. Planes related to icosahedral fivefold and pseudo-twofold symmetry are identified. Possible orthogonal cells bounded by twofold symmetry-related planes have been determined. Mg 4 Zn 7 phase growing on an icosahedral phase exhibits a number of planar faults parallel to the monoclinic axis, presumably to accommodate the quasiperiodicity at the interface. Two faults were identified, which were on {200} and { 2 ¯ 01} planes. Their structures have been determined by high resolution imaging in TEM. They produce two different unit cells at the interface. Full article
(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)
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Open AccessCommunication A Phononic Crystal-Based High Frequency Rheometer
Crystals 2018, 8(5), 195; https://doi.org/10.3390/cryst8050195
Received: 16 March 2018 / Revised: 19 April 2018 / Accepted: 29 April 2018 / Published: 1 May 2018
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Abstract
Dynamic Mechanical Analysis (DMA) allows for the measurement of the complex shear modulus of an elastomer. Measurements at frequencies above the frequency range of the device can be reached thanks to the Time–Temperature Equivalence principle. Yet, frequencies higher than a few kHz are
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Dynamic Mechanical Analysis (DMA) allows for the measurement of the complex shear modulus of an elastomer. Measurements at frequencies above the frequency range of the device can be reached thanks to the Time–Temperature Equivalence principle. Yet, frequencies higher than a few kHz are not attainable. Here, we propose a method exploiting the physics of bubble phononic crystals to measure the complex shear modulus at frequencies of a few tens of kHz. The idea is to fabricate a phononic crystal by creating a period arrangement of bubbles in the elastomer of interest, here PolyDiMethylSiloxane (PDMS), and to measure its transmission against frequency. Fitting the results with an analytic model provides both the loss and storage moduli. Physically, the shear storage modulus drives the position of the dip observed in transmission while the loss modulus controls the damping, and thus the level of transmission. Using this method, we are able to compare the high-frequency rheological properties of two commercial PDMS and to monitor the ageing process. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle Effect of Al–Mg Alloy Infiltration on Mechanical and Electrical Properties for Carbon/Carbon Composites
Crystals 2018, 8(5), 196; https://doi.org/10.3390/cryst8050196
Received: 18 March 2018 / Revised: 28 April 2018 / Accepted: 30 April 2018 / Published: 2 May 2018
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Abstract
Under vacuum Al–Mg alloy, liquids were successfully infiltrated into carbon/carbon (C/C) composites at high temperatures. Then, the mechanical properties, the metallographics, the scanning electron microscope images, the transmission electron microscope images, the X-ray diffraction images, and the energy dispersive spectroscopy results of C/C–Al–Mg
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Under vacuum Al–Mg alloy, liquids were successfully infiltrated into carbon/carbon (C/C) composites at high temperatures. Then, the mechanical properties, the metallographics, the scanning electron microscope images, the transmission electron microscope images, the X-ray diffraction images, and the energy dispersive spectroscopy results of C/C–Al–Mg composites were analyzed. The result showed that the bending property of C/C–Al–Mg composites reached 183 MPa whereas that of C/C composites totaled 165 MPa. The compressive strength of C/C–Al–Mg measured 206 MPa whereas that of C/C composites amounted to 142 MPa. The flexural strength and compressive strengths of the steeped metal sliders measured 121 and 104 MPa, respectively. The alloy liquid infiltrated into the matrix by forming a “network conduction” structure which reduced the resistivity and improved the conductivity of the composites. The resistivity of C/C–Al–Mg totaled 1.63 µΩm whereas that of C/C was 3.56 μΩm. During infiltration, an excellent wettability was observed between Al and the carbon matrix due to the existence of Al4C3. The friction coefficients of C/C, the steeped metal slide, and C/Al–Mg were 0.152, 0.068, and 0.189, respectively. The properties of C/C–Al–Mg composites meet the performance requirements of locomotive pantograph sliders. Full article
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Open AccessArticle A New Method for Evaluating the Indentation Toughness of Hardmetals
Crystals 2018, 8(5), 197; https://doi.org/10.3390/cryst8050197
Received: 2 March 2018 / Revised: 29 March 2018 / Accepted: 25 April 2018 / Published: 3 May 2018
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Abstract
This paper proposes a new method of evaluating the indentation toughness of hardmetals using the length of Palmqvist cracks (C) and Vickers indentation diagonal size (di). Indentation load “P” is divided into two parts: Pi
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This paper proposes a new method of evaluating the indentation toughness of hardmetals using the length of Palmqvist cracks (C) and Vickers indentation diagonal size (di). Indentation load “P” is divided into two parts: Pi for plastic indentation size and Pc for Palmqvist cracks. Pi depends upon the square of the indentation size (di2) and Pc depends upon (C3/2). The new method produces a very good linear relationship between the calculated indentation toughness values and the standard conventional linear elastic fracture mechanics toughness values with the same cemented carbide materials for a large number of standard Kennametal grades for both straight WC-Co carbide grades and grades containing cubic carbides. The new method also works on WC-Co hardmetal data selected from recently published literature. The technique compares the indentation toughness values of WC-Co materials before and after vacuum annealing at high temperature. The indentation toughness values of annealed carbide samples were lower than for un-annealed WC-Co hardmetals. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Study on Neutron Irradiation-Induced Structural Defects of GaN-Based Heterostructures
Crystals 2018, 8(5), 198; https://doi.org/10.3390/cryst8050198
Received: 25 April 2018 / Revised: 2 May 2018 / Accepted: 2 May 2018 / Published: 3 May 2018
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Abstract
The GaN-based heterostructures and related HEMTs (High Electron Mobility Transistors) were investigated by 1MeV neutrons at fluences up to 1015 cm−2, yielding an increase of the densities of screw dislocations and edge dislocations for GaN-based heterostructures. It gave the result
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The GaN-based heterostructures and related HEMTs (High Electron Mobility Transistors) were investigated by 1MeV neutrons at fluences up to 1015 cm−2, yielding an increase of the densities of screw dislocations and edge dislocations for GaN-based heterostructures. It gave the result that neutron irradiation-induced structural defects into GaN-based materials, and the irradiation-induced dislocations would propagate to the material surface causing surface morphology deterioration. However, the GaN-based material strain was robust to neutrons, and the more initial dislocations, the easier to generate irradiation defects and thus, more strongly affecting the electrical property degradations of materials and devices. Meanwhile, the reduction of the two-dimensional electron gas (2DEG) concentration (ns) caused by irradiation-induced defects led to the reducing the drain current. Moreover, the significant degradation of the reverse gate leakage current at fluences ranging from 1014 to 1015 cm−2 could be attributed to the irradiation-induced deep defects. The neutron induced damage was more difficult to anneal recovery than other particles, due to the neutron irradiation-induced deep levels and defect complexes such as defect clusters. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Structural Phase Transition and Compressibility of CaF2 Nanocrystals under High Pressure
Crystals 2018, 8(5), 199; https://doi.org/10.3390/cryst8050199
Received: 19 March 2018 / Revised: 26 April 2018 / Accepted: 26 April 2018 / Published: 3 May 2018
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Abstract
The structural phase transition and compressibility of CaF2 nanocrystals with size of 23 nm under high pressure were investigated by synchrotron X-ray diffraction measurement. A pressure-induced fluorite to α-PbCl2-type phase transition starts at 9.5 GPa and completes at 20.2 GPa.
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The structural phase transition and compressibility of CaF2 nanocrystals with size of 23 nm under high pressure were investigated by synchrotron X-ray diffraction measurement. A pressure-induced fluorite to α-PbCl2-type phase transition starts at 9.5 GPa and completes at 20.2 GPa. The phase-transition pressure is lower than that of 8 nm CaF2 nanocrystals and closer to bulk CaF2. Upon decompression, the fluorite and α-PbCl2-type structure co-exist at the ambient pressure. The bulk modulus B0 of the 23 nm CaF2 nanocrystals for the fluorite and α-PbCl2-type phase are 103(2) and 78(2) GPa, which are both larger than those of the bulk CaF2. The CaF2 nanocrystals exhibit obviously higher incompressibility compare to bulk CaF2. Further analysis demonstrates that the defect effect in our CaF2 nanocrystals plays a dominant role in the structural stability. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Copper(II) Complexes Based on Aminohydroxamic Acids: Synthesis, Structures, In Vitro Cytotoxicities and DNA/BSA Interactions
Crystals 2018, 8(5), 201; https://doi.org/10.3390/cryst8050201
Received: 29 March 2018 / Revised: 26 April 2018 / Accepted: 27 April 2018 / Published: 3 May 2018
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Abstract
Four complexes, [Cu2(glyha)(bpy)2(H2O)]·2ClO4·H2O (1), [Cu2(glyha)(phen)2]·2ClO4 (2), [Cu2(alaha)(bpy)2Cl]·Cl·4H2O (3), and [{Cu2(alaha)(phen)2}{Cu2(alaha)(phen)
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Four complexes, [Cu2(glyha)(bpy)2(H2O)]·2ClO4·H2O (1), [Cu2(glyha)(phen)2]·2ClO4 (2), [Cu2(alaha)(bpy)2Cl]·Cl·4H2O (3), and [{Cu2(alaha)(phen)2}{Cu2(alaha)(phen)2(NO3)}]·3NO3 (4) (glyha2− = dianion glycinehydroxamic acid, alaha2− = dianion alaninehydroxamic acid, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been successfully synthesized and characterized by X-ray single crystal diffraction. The interactions of these complexes with calf thymus DNA (CT-DNA) were studied through UV spectroscopy, fluorescence spectroscopy, and circular dichroism. The results revealed that complexes 14 could interact with CT-DNA through intercalation. Interactions of all complexes with bovine serum albumin (BSA) were confirmed by the docking study to quench the intrinsic fluorescence of BSA in a static quenching process. Furthermore, the in vitro cytotoxic effect of the complexes was also examined on four tumor cell lines, including human lung carcinoma cell line (A549), human colon carcinoma cell line (HCT-116), human promyelocytic leukemia cell (HL-60) and cervical cancer cell line (HeLa). All complexes exhibited different antitumor activities. Full article
(This article belongs to the Section Biomolecular Crystals)
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Open AccessArticle On the Phase Diagrams of 4He Adsorbed on Graphene and Graphite from Quantum Simulation Methods
Crystals 2018, 8(5), 202; https://doi.org/10.3390/cryst8050202
Received: 1 April 2018 / Revised: 28 April 2018 / Accepted: 29 April 2018 / Published: 4 May 2018
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Abstract
The ground-state phase diagrams of 4 He adsorbed on graphene and graphite are calculated using quantum simulation methods. In this work, a systematic investigation of the approximations used in such simulations is carried out. Particular focus is placed on the helium–helium (He–He) and
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The ground-state phase diagrams of 4 He adsorbed on graphene and graphite are calculated using quantum simulation methods. In this work, a systematic investigation of the approximations used in such simulations is carried out. Particular focus is placed on the helium–helium (He–He) and helium–carbon (He–C) interactions, as well as their modern approximations. On careful consideration of other approximations and convergence, the simulations are otherwise (numerically) exact. The He–He interaction as approximated by a sum of pairwise potentials is quantitatively assessed. A similar analysis is made for the He–C interaction, but more thoroughly and with a focus on surface corrugation. The importance of many-body effects is discussed. Altogether, the results provide “reference data” for the considered systems. Using comparisons with experiments and first-principle calculations, conclusions are drawn regarding the quantitative accuracy of these modern approximations to these interactions. Full article
(This article belongs to the Special Issue Quantum Crystals)
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Open AccessArticle The Rietveld Refinement in the EXPO Software: A Powerful Tool at the End of the Elaborate Crystal Structure Solution Pathway
Crystals 2018, 8(5), 203; https://doi.org/10.3390/cryst8050203
Received: 13 April 2018 / Revised: 30 April 2018 / Accepted: 2 May 2018 / Published: 4 May 2018
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Abstract
The Rietveld method is the most reliable and powerful tool for refining crystal structure when powder diffraction data are available. It requires that the structure model to be adjusted is as close as possible to the true structure. The Rietveld method usually represents
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The Rietveld method is the most reliable and powerful tool for refining crystal structure when powder diffraction data are available. It requires that the structure model to be adjusted is as close as possible to the true structure. The Rietveld method usually represents the final step of the powder solution process, in particular when a new structure is going to be determined and published. EXPO is a software able to execute all the steps of the solution process in a mostly automatic way, by starting from the chemical formula and the experimental diffraction pattern, passing through computational methods for locating the structure model and optimizing it, and ending to the Rietveld refinement. In this contribution, we present the most recent solution strategies in EXPO, both in reciprocal and direct space, aiming at obtaining models suitable to be refined by the Rietveld method. Examples of Rietveld refinements are described, whose results are related to different solution procedures and types of compounds (organic and inorganic). Full article
(This article belongs to the Special Issue Rietveld Refinement in the Characterization of Crystalline Materials)
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Open AccessArticle Mixed Sr and Ba Tri-Stannides/Plumbides AII(Sn1−xPbx)3
Crystals 2018, 8(5), 204; https://doi.org/10.3390/cryst8050204
Received: 2 April 2018 / Revised: 25 April 2018 / Accepted: 26 April 2018 / Published: 4 May 2018
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Abstract
The continuous substitution of tin by lead (M IV ) allows for the exploration geometric criteria for the stability of the different stacking variants of alkaline-earth tri-tetrelides AIIM3IV . A series of ternary Sr and Ba mixed tri-stannides/plumbides
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The continuous substitution of tin by lead (M IV ) allows for the exploration geometric criteria for the stability of the different stacking variants of alkaline-earth tri-tetrelides A II M 3 IV . A series of ternary Sr and Ba mixed tri-stannides/plumbides A II (Sn 1 x Pb x ) 3 (A II = Sr, Ba) was synthesized from stoichiometric mixtures of the elements. Their structures were determined by means of single crystal X-ray data. All structures exhibit close packed ordered A M 3 layers containing M kagomé nets. Depending on the stacking sequence, the resulting M polyanion resembles the oxygen substructure of the hexagonal (face-sharing octahedra, h stacking, Ni 3 Sn-type, border compound BaSn 3 ) or the cubic (corner-sharing octahedra, c stacking, Cu 3 Au-type, border compound SrPb 3 ) perovskite. In the binary compound BaSn 3 (Ni 3 Sn-type) up to 28% of Sn can be substituted against Pb (hP8, P 6 3 / mmc, x = 0.28(4): a = 726.12(6), c = 556.51(6) pm, R1 = 0.0264). A further increased lead content of 47 to 66% causes the formation of the BaSn 2.57 Bi 0.43 -type structure with a ( hhhc ) 2 stacking [hP32, P 6 3 / mmc, x = 0.47(3): a = 726.80(3), c = 2235.78(14) pm, R1 = 0.0437]. The stability range of the BaPb 3 -type sequence ( hhc ) 3 starts at a lead proportion of 78% (hR36, R 3 ¯ m, a = 728.77(3), c = 2540.59(15) pm, R1= 0.0660) and reaches up to the pure plumbide BaPb 3 . A second new polymorph of BaPb 3 forms the Mg 3 In-type structure with a further increased amount of cubic sequences [ ( hhcc ) 3 ; hR48, a = 728.7(2), c = 3420.3(10) pm, R1 = 0.0669] and is thus isotypic with the border phase SrSn 3 of the respective strontium series. For the latter, a Pb content of 32% causes a small existence region of the PuAl 3 -type structure [hP24, P 6 3 / mmc, a = 696.97(6), c = 1675.5(2) pm, R1 = 0.1182] with a ( hcc ) 2 stacking. The series is terminated by the pure c stacking of SrPb 3 , the stability range of this structure type starts at 75% Pb (cP4, Pm 3 ¯ m; a = 495.46(9) pm, R1 = 0.0498). The stacking of the close packed layers is evidently determined by the ratio of the atomic radii of the contributing elements. The Sn/Pb distribution inside the polyanion (’coloring’) is likewise determined by size criteria. The electronic stability ranges, which are discussed on the basis of the results of FP-LAPW band structure calculations are compared with the Zintl concept and Wade’s/mno electron counting rules. Still, due to the presence of only partially occupied steep M-p bands the compounds are metals exhibiting pseudo band gaps close to the Fermi level. Thus, this structure family represents an instructive case for the transition from polar ionic/covalent towards (inter)metallic chemistry. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Lu5Pd4Ge8 and Lu3Pd4Ge4: Two More Germanides among Polar Intermetallics
Crystals 2018, 8(5), 205; https://doi.org/10.3390/cryst8050205
Received: 20 April 2018 / Revised: 3 May 2018 / Accepted: 3 May 2018 / Published: 5 May 2018
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Abstract
In this study, two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4
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In this study, two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4Ge8 is monoclinic, P21/m, mP34, a = 5.7406(3), b = 13.7087(7), c = 8.3423(4) Å, β = 107.8(1), Z = 2; Lu3Pd4Ge4 is orthorhombic, Immm, oI22, a = 4.1368(3), b = 6.9192(5), c = 13.8229(9) Å, Z = 2. The Lu5Pd4Ge8 analysed crystal is one more example of non-merohedral twinning among the rare earth containing germanides. Chemical bonding DFT studies were conducted for these polar intermetallics and showing a metallic-like behavior. Gathered results for Lu5Pd4Ge8 and Lu3Pd4Ge4 permit to described both of them as composed by [Pd–Ge]δ– three dimensional networks bonded to positively charged lutetium species. From the structural chemical point of view, the studied compounds manifest some similarities to the Zintl phases, containing well-known covalent fragment i.e., Ge dumbbells as well as unique cis-Ge4 units. A comparative analysis of molecular orbital diagrams for Ge26– and cis-Ge10– anions with COHP results supports the idea of the existence of complex Pd–Ge polyanions hosting covalently bonded partially polarised Ge units. The palladium atoms have an anion like behaviour and being the most electronegative cause the noticeable variation of Ge species charges from site to site. Lutetium charges oscillate around +1.5 for all crystallographic positions. Obtained results explained why the classical Zintl-Klemm concept can’t be applied for the studied polar intermetallics. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle Synthesis, Crystal Structures, and Anti-Liver Cancer Activity Studies on Three Similar Coordination Polymers
Crystals 2018, 8(5), 207; https://doi.org/10.3390/cryst8050207
Received: 22 April 2018 / Revised: 8 May 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
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Abstract
By employment of a pre-designed molecular building block [(pzTp)Fe(CN)3], one cyano-bridged trinuclear complex [MnMe4TACD][(pzTp)Fe(CN)3]2(H2O)161, [pzTp = tetrakis(pyrazoly)borate, Me4TACD = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane] and two 1D chain-like coordination polymers {[(pzTp)Fe(CN)3
[...] Read more.
By employment of a pre-designed molecular building block [(pzTp)Fe(CN)3], one cyano-bridged trinuclear complex [MnMe4TACD][(pzTp)Fe(CN)3]2(H2O)16 1, [pzTp = tetrakis(pyrazoly)borate, Me4TACD = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane] and two 1D chain-like coordination polymers {[(pzTp)Fe(CN)3]2[M(Bim)2](H2O)2}n [M = Cu(II) for 2 and Mn(II) for 3, Bim = bis(1-imidazolyl)methane] were synthesized by making use of different nitrogen-containing organic linkers. Furthermore, in vitro cytotoxicity of compounds 13 was studied against four human liver cancer cells (HepG2, Bel-7402, SMMC7721, and MHCC97) via the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) assay experiments. Full article
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Open AccessArticle Optical Absorption and Reflectivity of a Molecular Cluster of Lithium Niobate Adsorbed on a Graphene Layer
Crystals 2018, 8(5), 208; https://doi.org/10.3390/cryst8050208
Received: 15 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
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Abstract
We used density functional theory to study the adsorption of a molecular cluster of lithium niobate (LiNbO3) on a graphene layer. The cluster size is about 1.2 nm, and it has 11 molecules. We optimized the cluster, and then we calculated
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We used density functional theory to study the adsorption of a molecular cluster of lithium niobate (LiNbO3) on a graphene layer. The cluster size is about 1.2 nm, and it has 11 molecules. We optimized the cluster, and then we calculated its interaction with the optimized graphene layer. We found that the cluster is adsorbed on the graphene layer with an adsorption energy of −2.2213 eV (−0.068 eV/atom). Afterwards, we calculated the reflectivity, and the optical absorption coefficients of the system cluster-graphene and of a graphene layer alone, to make a comparison. We found large differences in the values of these properties of the new system, with respect to the corresponding ones of graphene. We performed our calculations using the general gradient approximation (GGA), and the GGA modified for van der Waals interactions in order to take into account the long-range correlations. Full article
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Open AccessArticle High-Pressure Elastic, Vibrational and Structural Study of Monazite-Type GdPO4 from Ab Initio Simulations
Crystals 2018, 8(5), 209; https://doi.org/10.3390/cryst8050209
Received: 19 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
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Abstract
The GdPO4 monazite-type has been studied under high pressure by first principles calculations in the framework of density functional theory. This study focuses on the structural, dynamical, and elastic properties of this material. Information about the structure and its evolution under pressure,
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The GdPO4 monazite-type has been studied under high pressure by first principles calculations in the framework of density functional theory. This study focuses on the structural, dynamical, and elastic properties of this material. Information about the structure and its evolution under pressure, the equation of state, and its compressibility are reported. The evolution of the Raman and Infrared frequencies, as well as their pressure coefficients are also presented. Finally, the study of the elastic constants provides information related with the elastic and mechanical properties of this compound. From our results, we conclude that monazite-type GdPO4 becomes mechanically unstable at 54 GPa; no evidence of soft phonons has been found up to this pressure at the zone center. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Lattice Parameters of Optical Damage Resistant In-Doped LiNbO3 Crystals
Crystals 2018, 8(5), 210; https://doi.org/10.3390/cryst8050210
Received: 17 April 2018 / Revised: 2 May 2018 / Accepted: 3 May 2018 / Published: 13 May 2018
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Abstract
The lattice parameters in optical damage resistant crystal LiNbO3-In were measured for the first time using the X-ray powder method with an internal standard, which provides a high accuracy of the results. The lattice parameters vs. In concentration were obtained in
[...] Read more.
The lattice parameters in optical damage resistant crystal LiNbO3-In were measured for the first time using the X-ray powder method with an internal standard, which provides a high accuracy of the results. The lattice parameters vs. In concentration were obtained in the concentration range from 0.24 to 3.2 at % In in the crystal. The results are discussed in the framework of currently accepted model of the LiNbO3 intrinsic defect structure. Full article
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Open AccessArticle Optimization of Ca14MgSb11 through Chemical Substitutions on Sb Sites: Optimizing Seebeck Coefficient and Resistivity Simultaneously
Crystals 2018, 8(5), 211; https://doi.org/10.3390/cryst8050211
Received: 17 April 2018 / Revised: 6 May 2018 / Accepted: 8 May 2018 / Published: 13 May 2018
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Abstract
In thermoelectric materials, chemical substitutions are widely used to optimize thermoelectric properties. The Zintl phase compound, Yb14MgSb11, has been demonstrated as a promising thermoelectric material at high temperatures. It is iso-structural with Ca14AlSb11 with space
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In thermoelectric materials, chemical substitutions are widely used to optimize thermoelectric properties. The Zintl phase compound, Yb14MgSb11, has been demonstrated as a promising thermoelectric material at high temperatures. It is iso-structural with Ca14AlSb11 with space group I41/acd. Its iso-structural analog, Ca14MgSb11, was discovered to be a semiconductor and have vacancies on the Sb(3) sites, although in its nominal composition it can be described as consisting of fourteen Ca2+ cations with one [MgSb4]9− tetrahedron, one Sb37− linear anion and four isolated Sb3− anions (Sb(3) site) in one formula unit. When Sn substitutes Sb in Ca14MgSb11, optimized Seebeck coefficient and resistivity were achieved simultaneously although the Sn amount is small (<2%). This is difficult to achieve in thermoelectric materials as the Seebeck coefficient and resistivity are inversely related with respect to carrier concentration. Thermal conductivity of Ca14MgSb11-xSnx remains almost the same as Ca14MgSb11. The calculated zT value of Ca14MgSb10.80Sn0.20 reaches 0.49 at 1075 K, which is 53% higher than that of Ca14MgSb11 at the same temperature. The band structure of Ca14MgSb7Sn4 is calculated to simulate the effect of Sn substitutions. Compared to the band structure of Ca14MgSb11, the band gap of Ca14MgSb7Sn4 is smaller (0.2 eV) and the Fermi-level shifts into the valence band. The absolute values for density of states (DOS) of Ca14MgSb7Sn4 are smaller near the Fermi-level at the top of valence band and 5p-orbitals of Sn contribute most to the valence bands near the Fermi-level. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessArticle New Polymorphs of the Phase-Change Material Sodium Acetate
Crystals 2018, 8(5), 213; https://doi.org/10.3390/cryst8050213
Received: 15 March 2018 / Revised: 6 May 2018 / Accepted: 8 May 2018 / Published: 15 May 2018
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Abstract
Two new polymorphs of the phase-change material sodium acetate were characterized by single-crystal X-ray diffraction. A tetragonal form was found first. It converted to a orthorhombic form after measurement of a single crystal of the tetragonal form at 100 K and subsequent warming
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Two new polymorphs of the phase-change material sodium acetate were characterized by single-crystal X-ray diffraction. A tetragonal form was found first. It converted to a orthorhombic form after measurement of a single crystal of the tetragonal form at 100 K and subsequent warming to ambient temperature. Hirshfeld surface fingerprint plots show the different packing environments of the two new compared to the two known orthorhombic polymorphs Forms I and II. The accuracy and precision of the structures were improved compared to conventional independent atom model refinement through the use of aspherical scattering factors of the invariom database. We think that the layered nature of all sodium acetate forms, and the thereby limited (“quantized”) availability of vibrational modes, is related to the phenomenon of supersaturation, which is connected to its phase-change properties. Full article
(This article belongs to the Special Issue Experimental and Theoretical Electron Density Analysis of Crystals)
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Open AccessArticle Polaron-Mediated Luminescence in Lithium Niobate and Lithium Tantalate and Its Domain Contrast
Crystals 2018, 8(5), 214; https://doi.org/10.3390/cryst8050214
Received: 6 April 2018 / Revised: 27 April 2018 / Accepted: 29 April 2018 / Published: 15 May 2018
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Abstract
In this review article, we discuss photoluminescence phenomena mediated by polarons in lithium niobate (LNO). At first we present the fundamentals on polaron states in LNO and their energy levels, i.e., on free and bound electron polarons, on hole polarons as well as
[...] Read more.
In this review article, we discuss photoluminescence phenomena mediated by polarons in lithium niobate (LNO). At first we present the fundamentals on polaron states in LNO and their energy levels, i.e., on free and bound electron polarons, on hole polarons as well as on bipolarons. We discuss the absorption measurements on reduced as well as on doped LNO that made the characterization of the formed polaron states possible by their absorption bands. Next, we proceed by reporting on the two polaron-mediated photoluminescence bands that have been observed in LNO: (1) A near-infrared luminescence band in the range of 1.5 eV shows a mono-exponential decay and a strong dependence on iron doping. This luminescence is emitted by bound polarons returning from an excited state to the ground state. (2) A luminescence band at visible wavelengths with a maximum at 2.6 eV shows a stretched-exponential decay and is strongly enhanced by optical damage resistant doping around the doping threshold. This luminescence stems from the recombination of free electron and hole polarons. The next major topic of this review are domain contrasts of the visible photoluminescence that have been observed after electrical poling of the substrate, as singly inverted domains show a slightly reduced and faster decaying luminescence. Subsequent annealing results in an exponential decrease of that domain contrast. We show that this contrast decay is strongly related to the mobility of lithium ions, thus confirming the role of polar defect complexes, including lithium vacancies, for these domain contrasts. Finally we discuss the extension of our investigations to lithium tantalate (LTO) samples. While the results on the domain contrast and its decay are similar to LNO, there are remarkable differences in their luminescence spectra. Full article
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Open AccessArticle Mild Synthesis and Structural Characterization of a Novel Vanadyl Selenite-Hydrogen Selenite Phase, Na[VO(SeO3)(HSeO3)]·1,5H2O
Crystals 2018, 8(5), 215; https://doi.org/10.3390/cryst8050215
Received: 16 March 2018 / Revised: 7 May 2018 / Accepted: 13 May 2018 / Published: 15 May 2018
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Abstract
Single crystals of Na[VO(SeO3)(HSeO3)]·1,5H2O have been prepared by solvent slow evaporation from an equimolar aqueous mixture of sodium selenite and vanadyl sulfate. The overall arrangement consists of VO6 octahedra, [SeO3]2− and [HSeO3
[...] Read more.
Single crystals of Na[VO(SeO3)(HSeO3)]·1,5H2O have been prepared by solvent slow evaporation from an equimolar aqueous mixture of sodium selenite and vanadyl sulfate. The overall arrangement consists of VO6 octahedra, [SeO3]2− and [HSeO3] anions forming a strong backbone with channel-like voids, while sodium cations participate in the framework, ensuring the overall charge balance. The crystal packing of the material features channels with a star-shaped section showing a mean aperture of 6.10 Å with the oxygen atoms of the V=O moieties pointing towards the interior of the cavities. Their dimensions are the narrowest reported until now in vanadium selenite compounds. Disordered sodium cations with occupancy factor of 0.5 are found in the star-shaped section cavities together with disordered water molecules, interacting with each other via hydrogen bonds. Full article
(This article belongs to the Special Issue Crystal Structures of Compounds Containing Ions Selenite)
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Open AccessArticle One-Step Synthesis of Cu–ZnO@C from a 1D Complex [Cu0.02Zn0.98(C8H3NO6)(C12H8N2)]n for Catalytic Hydroxylation of Benzene to Phenol
Crystals 2018, 8(5), 218; https://doi.org/10.3390/cryst8050218
Received: 3 May 2018 / Revised: 13 May 2018 / Accepted: 14 May 2018 / Published: 16 May 2018
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Abstract
A novel one-dimensional bimetallic complex [Cu0.02Zn0.98(C8H3NO6)(C12H8N2)]n (“Complex”) has been synthesized by a hydrothermal method. A Cu–ZnO@C composite was obtained by a one-step pyrolysis of Complex. Correlated
[...] Read more.
A novel one-dimensional bimetallic complex [Cu0.02Zn0.98(C8H3NO6)(C12H8N2)]n (“Complex”) has been synthesized by a hydrothermal method. A Cu–ZnO@C composite was obtained by a one-step pyrolysis of Complex. Correlated with the characterization results, it is confirmed that both metallic Cu0 and ZnO nanoparticles were highly dispersed on/in the carbon substrate. This simple one-step pyrolysis method avoids the high-temperature pretreatment under H2 commonly required for preparation of such Cu–ZnO catalysts. The Cu–ZnO@C composite was tested with respect to its catalytic activities for the hydroxylation of benzene to phenol with H2O2. The results indicate that the benzene conversion, phenol yield, and phenol selectivity reached the maximum values (55.7%, 32%, and 57.5%, respectively) at Complex carbonized at 600 °C, and were higher than those of the commercial mixed sample. Compared with the other candidate catalysts, the turnover frequency (TOF) of our Cu–ZnO@C catalyst (117.9 mmol mol−1 s−1) can be ranked at the top. The higher catalytic activities should be due to the highly dispersed metallic Cu0 and ZnO particles as well as their synergistic interaction. Full article
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Open AccessArticle Recent Insights into Protein Crystal Nucleation
Crystals 2018, 8(5), 219; https://doi.org/10.3390/cryst8050219
Received: 27 April 2018 / Revised: 9 May 2018 / Accepted: 12 May 2018 / Published: 17 May 2018
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Abstract
Homogeneous nucleation of protein crystals in solution is tackled from both thermodynamic and energetic perspectives. The entropic contribution to the destructive action of water molecules which tend to tear up the crystals and to their bond energy is considered. It is argued that,
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Homogeneous nucleation of protein crystals in solution is tackled from both thermodynamic and energetic perspectives. The entropic contribution to the destructive action of water molecules which tend to tear up the crystals and to their bond energy is considered. It is argued that, in contrast to the crystals’ bond energy, the magnitude of destructive energy depends on the imposed supersaturation. The rationale behind the consideration presented is that the critical nucleus size is determined by the balance between destructive and bond energies. By summing up all intra-crystal bonds, the breaking of which is needed to disintegrate a crystal into its constituting molecules, and using a crystallographic computer program, the bond energy of the closest-packed crystals is calculated (hexagonal closest-packed crystals are given as an example). This approach is compared to the classical mean work of separation (MWS) method of Stranski and Kaischew. While the latter is applied merely for the so-called Kossel-crystal and vapor grown crystals, the approach presented can be used to establish the supersaturation dependence of the protein crystal nucleus size of arbitrary lattice structures. Full article
(This article belongs to the Special Issue Biological Crystallization)
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Open AccessArticle Metal Halide Perovskite Single Crystals: From Growth Process to Application
Crystals 2018, 8(5), 220; https://doi.org/10.3390/cryst8050220
Received: 21 April 2018 / Revised: 9 May 2018 / Accepted: 9 May 2018 / Published: 17 May 2018
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Abstract
As a strong competitor in the field of optoelectronic applications, organic-inorganic metal hybrid perovskites have been paid much attention because of their superior characteristics, which include broad absorption from visible to near-infrared region, tunable optical and electronic properties, high charge mobility, long exciton
[...] Read more.
As a strong competitor in the field of optoelectronic applications, organic-inorganic metal hybrid perovskites have been paid much attention because of their superior characteristics, which include broad absorption from visible to near-infrared region, tunable optical and electronic properties, high charge mobility, long exciton diffusion length and carrier recombination lifetime, etc. It is noted that perovskite single crystals show remarkably low trap-state densities and long carrier diffusion lengths, which are even comparable with the best photovoltaic-quality silicon, and thus are expected to provide better optoelectronic performance. This paper reviews the recent development of crystal growth in single-, mixed-organic-cation and fully inorganic halide perovskite single crystals, in particular the solution approach. Furthermore, the application of metal hybrid perovskite single crystals and future perspectives are also highlighted. Full article
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Open AccessArticle Synthesis and Crystal Structures of Cadmium(II) Cyanide with Branched-Butoxyethanol
Crystals 2018, 8(5), 221; https://doi.org/10.3390/cryst8050221
Received: 27 December 2017 / Revised: 12 March 2018 / Accepted: 15 May 2018 / Published: 17 May 2018
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Abstract
Two novel 3D cadmium(II) cyanide coordination polymers with branched-butoxyethanol compounds (iBucel = iso-butoxyethanol, tBucel = tert-butoxyethanol), [{Cd(CN)2(iBucel)2}{Cd(CN)2(H2O)(iBucel)}2{Cd(CN)2}6∙2(iBucel)]nI and [{Cd(CN)2(H2O)1.06(tBucel)0.94
[...] Read more.
Two novel 3D cadmium(II) cyanide coordination polymers with branched-butoxyethanol compounds (iBucel = iso-butoxyethanol, tBucel = tert-butoxyethanol), [{Cd(CN)2(iBucel)2}{Cd(CN)2(H2O)(iBucel)}2{Cd(CN)2}6∙2(iBucel)]n I and [{Cd(CN)2(H2O)1.06(tBucel)0.94}{Cd(CN)2(tBucel)}2{Cd(CN)2}2∙1.06(tBucel)]n II, were synthesized and characterized by structural determination. Complex I contains two distinct Cd(II) coordination geometries: octahedral and tetrahedral. In contrast, complex II contains three distinct Cd(II) coordination geometries: octahedral, square-pyramidal, and tetrahedral. In the two complexes, branched-butoxyethanol molecules behave as both a ligand and a guest in the Cd(CN)2 cavities. The framework in I contains octahedral and tetrahedral Cd(II) in a 3:6 ratio. In I, the coordination environments of octahedral Cd(II) are cis-O-Cd-O. The framework in II contains octahedral, square-pyramidal, and tetrahedral Cd(II) in a 1:2:2 ratio. In II, the coordination environment of octahedral Cd(II) is disordered trans-O-Cd-O and the axial oxygen ligand is either a water or tBucel molecule. In II, the square-pyramidal Cd(II) geometry is formed by one tBucel ligand and four cyanide ligands. The Cd(CN)2 frameworks of the two complexes exhibit different structures. 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 Calcium and Phosphate on Compositional Conversion from Dicalcium Hydrogen Phosphate Dihydrate Blocks to Octacalcium Phosphate Blocks
Crystals 2018, 8(5), 222; https://doi.org/10.3390/cryst8050222
Received: 23 April 2018 / Revised: 8 May 2018 / Accepted: 16 May 2018 / Published: 17 May 2018
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Abstract
Octacalcium phosphate (OCP) has attracted much attention as an artificial bone substitute because of its excellent osteoconductive and bone replacement properties. Although numerous studies have investigated OCP powder fabrication, there are only a few studies on OCP block fabrication. Therefore, in this study,
[...] Read more.
Octacalcium phosphate (OCP) has attracted much attention as an artificial bone substitute because of its excellent osteoconductive and bone replacement properties. Although numerous studies have investigated OCP powder fabrication, there are only a few studies on OCP block fabrication. Therefore, in this study, the feasibility of optimizing dicalcium hydrogen phosphate dihydrate (DCPD) blocks, as a precursor for OCP block fabrication, under a pH 6 adjusted acetate buffer solution at 70 °C for 2 days was investigated. When a DCPD block was immersed in acetate buffer, the block was partially converted to OCP, with a large amount of dicalcium hydrogen phosphate anhydrate (DCPA), and its macroscopic structure was maintained. When the DCPD block was immersed in a Ca-containing solution, it was converted to mainly hydroxyapatite (HAp) with DCPA. On the other hand, when the DCPD block was immersed in a PO4-containing solution, the block was converted to OCP, and its macroscopic structure was maintained. In other words, the PO4-induced calcium phosphate with a Ca/P molar ratio lower than 1.0 may represent an intermediate phase during the compositional transformation from a DCPD block to an OCP block through the dissolution–precipitation reaction. Full article
(This article belongs to the Special Issue Biomimetic Growth of Calcium Phosphate Crystals)
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Open AccessArticle An Analytical Solution to Lumped Parameter Equivalent Circuit Model of Organic Solar Cells
Crystals 2018, 8(5), 224; https://doi.org/10.3390/cryst8050224
Received: 21 April 2018 / Revised: 6 May 2018 / Accepted: 17 May 2018 / Published: 18 May 2018
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Abstract
In this paper, an analytical and closed-form solution to the lumped parameter equivalent circuit model of organic solar cells is proposed to complete the simulations of the S-shaped I-V characteristics. Based on the model previously proposed by Mazhari, the set of
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In this paper, an analytical and closed-form solution to the lumped parameter equivalent circuit model of organic solar cells is proposed to complete the simulations of the S-shaped I-V characteristics. Based on the model previously proposed by Mazhari, the set of terminal current and voltage equations describing the three diodes is solved and the effects from the model parameters are illustrated. Our solutions are verified by being compared with the least square method results and experimental data, respectively. Good agreements show that our solution calculation scheme is not only both accurate and efficient, but also valid in the whole operation regime of solar cells, especially for the S-shaped kink on the condition where the terminal voltage is larger than the open circuit voltage. Such an analytical solution can play an important role in the simulations for I-V characteristics of solar cells, fast extractions of the model parameters, and implements into practical photovoltaic device simulators. Full article
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Open AccessCommunication Structural and Hirshfeld Surface Analyses of a Novel Hetero-Tetranuclear CuII-NaI Bis(Salamo)-Based Coordination Compound
Crystals 2018, 8(5), 227; https://doi.org/10.3390/cryst8050227
Received: 12 March 2018 / Revised: 15 May 2018 / Accepted: 16 May 2018 / Published: 18 May 2018
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Abstract
The newly designed butterfly-shaped hetero-tetranuclear CuII-NaI coordination compound, [Cu3(HL)2Na]∙Pic (Pic is abbreviation of picrate) (1) which is derived from a naphthalenediol-based bis(Salamo)-type chelating ligand H4L have been synthesized and characterized by
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The newly designed butterfly-shaped hetero-tetranuclear CuII-NaI coordination compound, [Cu3(HL)2Na]∙Pic (Pic is abbreviation of picrate) (1) which is derived from a naphthalenediol-based bis(Salamo)-type chelating ligand H4L have been synthesized and characterized by elemental analyses, UV-vis spectra, IR spectra analysis, and Hirshfeld surface analysis. X-ray crystallographic analyses revealed that the coordination compound 1 is a novel hetero-tetranuclear CuII-NaI bis(Salamo)-type coordination compound and it differs from heterotrinuclear CuII-NaI bis(Salamo)-type coordination compound reported earlier. The Cu1 and Cu3 atoms are tetra-coordinated with geometries of distorted square pyramid, while Cu2 atom are hexa-coordinated with the geometry of a distorted octahedron. The NaI atom is octa-coordinated with the geometry of a distorted hexagonal bipyramid. Furthermore, the supramolecular structure and Hirshfeld surface analyses have been discussed in detail. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Effect of Lithium Doping on Microstructural and Optical Properties of ZnO Nanocrystalline Films Prepared by the Sol-Gel Method
Crystals 2018, 8(5), 228; https://doi.org/10.3390/cryst8050228
Received: 28 April 2018 / Revised: 16 May 2018 / Accepted: 16 May 2018 / Published: 19 May 2018
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Abstract
The Zn1−xLixO (x = 0, 0.01, 0.03, and 0.05) nanocrystalline films were synthesized on silicon (Si) substrates by using the sol-gel method. The crystal structure and surface morphology of these films were investigated by X-ray diffraction (XRD) and field
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The Zn1−xLixO (x = 0, 0.01, 0.03, and 0.05) nanocrystalline films were synthesized on silicon (Si) substrates by using the sol-gel method. The crystal structure and surface morphology of these films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). We observed that the average grain size was gradually reduced with increasing doping Li content. Photoluminescence (PL) spectra show that increasing the Li content will deteriorate the crystalline quality and result in the decrease of ultraviolet emission from the excitonic recombination and the enhancement of visible emission from the recombination between the intrinsic defects. The current-voltage properties of Zn1−xLixO nanocrystalline films were also studied under dark and photo-illumination for photo-detection applications. The normalized photo-to-dark-current ratio (Iphoto − Idark)/Idark has been enhanced from 315 to 4161 by increasing the Li content of the Zn1−xLixO nanocrystalline films from zero to 0.05. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle A New Family of Heterometallic LnIII[12-MCFeIIIN(shi)-4] Complexes: Syntheses, Structures and Magnetic Properties
Crystals 2018, 8(5), 229; https://doi.org/10.3390/cryst8050229
Received: 21 April 2018 / Revised: 13 May 2018 / Accepted: 17 May 2018 / Published: 19 May 2018
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Abstract
A new family of LnIII [12-Metallacrown-4] compounds of formulas (C5H6N) [LnFe4(shi)4(C6H5COO)4(Py)4]·3.5Py [Ln = EuIII (1); GdIII (2); TbIII (
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A new family of LnIII [12-Metallacrown-4] compounds of formulas (C5H6N) [LnFe4(shi)4(C6H5COO)4(Py)4]·3.5Py [Ln = EuIII (1); GdIII (2); TbIII (3); DyIII (4); and, H3shi = salicylhydroxamic acid] were obtained through one-pot reactions with H3shi, Fe(NO3)3·9H2O, and, Ln(NO3)3·6H2O as reagents. Single-crystal X-ray analyses show that they are isostructural and have the similar [12-MCFeIII N(shi)-4] core, with four benzoate molecules bridging the central LnIII ion to the ring FeIII ions. The negative charge of the 12-MC-4 metallacrown is balanced by one pyridinium cation, which forms the hydrogen bond with an adjacent solvent pyridine molecule. Magnetic measurements demonstrate antiferromagnetic coupling interactions and field-induced slow magnetic relaxation in complex 4. Full article
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Open AccessArticle Self-Assembly of 3d-4f ZnII-LnIII (Ln = Ho and Er) Bis(salamo)-Based Complexes: Controlled Syntheses, Structures and Fluorescence Properties
Crystals 2018, 8(5), 230; https://doi.org/10.3390/cryst8050230
Received: 26 April 2018 / Revised: 13 May 2018 / Accepted: 19 May 2018 / Published: 20 May 2018
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Abstract
Two new hetero-trinuclear 3d-4f complexes [Zn2(L)Ho(μ2-OAc)2(OAc)(MeOH)]·CH2Cl2 (1) and [Zn2(L)Er(μ2-OAc)2]OAc (2), derived from a bis(salamo)-based ligand H4L, were synthesized and characterized via elemental
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Two new hetero-trinuclear 3d-4f complexes [Zn2(L)Ho(μ2-OAc)2(OAc)(MeOH)]·CH2Cl2 (1) and [Zn2(L)Er(μ2-OAc)2]OAc (2), derived from a bis(salamo)-based ligand H4L, were synthesized and characterized via elemental analyses, IR, UV–Vis, fluorescence spectra and X-ray crystallography. The X-ray crystal structure analyses demonstrated that two μ2-acetateanions bridge the ZnII and LnIII (Ln = Ho (1) and Er (2)) atoms in a μ2-fashion forming similar hetero-trinuclear structures, respectively. In complex 1, one methanol molecule as coordinating solvent participates in the coordination, the two ZnII atoms are six- and five-coordinated and have geometries of slightly distorted tetragonal pyramid and octahedron, and the HoIII atom is nine-coordinated and has the geometry of a mono-capped square antiprism. In complex 2, the two ZnII atoms both possess five-coordinated tetragonal pyramid geometries, and the ErIII atom is eight-coordinated with a square antiprism geometry. Furthermore, the fluorescence properties of complexes 1 and 2 were determined. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Transitions and Geometric Evolution of Cu309 Nanocluster during Slow Cooling Process
Crystals 2018, 8(5), 231; https://doi.org/10.3390/cryst8050231
Received: 12 April 2018 / Revised: 16 May 2018 / Accepted: 17 May 2018 / Published: 21 May 2018
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Abstract
Since the nucleation and growth of clusters is usually a non-equilibrium condensation process, a distribution of structural isomers for a given cluster size may be encountered even under the same conditions. In this work, molecular dynamics simulations are performed on sets of molten
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Since the nucleation and growth of clusters is usually a non-equilibrium condensation process, a distribution of structural isomers for a given cluster size may be encountered even under the same conditions. In this work, molecular dynamics simulations are performed on sets of molten clusters of Cu309 to study their structures at low temperatures while controlling the cooling rate. Several different final structures including perfect icosahedra (ICO), imperfect Mark’ decahedra (MDEC) and imperfect FCC truncated octahedra (TOCT) are obtained even at the same cooling rate. It is calculated that the most favorable structure is icosahedra, which becomes more and more favorable as the cooling rate is slowed. To better understand the process of crystallization, several techniques, including potential-temperature curves, common neighbor analysis (CNA) and radial distribution function (RDF), are used to analyze and study the structural transition. Results show that different structures are obtained under identical conditions due to the stochastic nature of nucleation and relatively small energy difference between isomers. The process of geometrical evolution for icosahedra is given by comparing and analyzing the time evolution of the root-mean-square deviation (RMSD) of atoms located in every shell. Full article
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Open AccessReview Growth of Metal Halide Perovskite, from Nanocrystal to Micron-Scale Crystal: A Review
Crystals 2018, 8(5), 182; https://doi.org/10.3390/cryst8050182
Received: 27 March 2018 / Revised: 17 April 2018 / Accepted: 17 April 2018 / Published: 24 April 2018
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Abstract
Metal halide perovskite both in the form of nanocrystal and thin films recently emerged as the most promising semiconductor material covering a huge range of potential applications from display technologies to photovoltaics. Colloidal inorganic and organic–inorganic hybrid metal halide perovskite nanocrystals (NCs) have
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Metal halide perovskite both in the form of nanocrystal and thin films recently emerged as the most promising semiconductor material covering a huge range of potential applications from display technologies to photovoltaics. Colloidal inorganic and organic–inorganic hybrid metal halide perovskite nanocrystals (NCs) have received tremendous attention due to their high photoluminescence quantum yields, while large grain perovskite films possess fewer defects, and a long diffusion length providing high-power conversion efficiency in planar devices. In this review, we summarize the different synthesis routes of metal halide perovskite nanocrystals and the recent methodologies to fabricate high-quality micron scale crystals in the form of films for planar photovoltaics. For the colloidal synthesis of halide perovskite NCs, two methods including ligand-assisted reprecipitation and hot injection are mainly applied, and the doping of metal ions in NCs as well as anion exchange reactions are widely used to tune their optical properties. In addition, recent growth methods and underlying mechanism for high-quality micron size crystals are also investigated, which are summarized as solution-process methods (including the anti-solvent method, solvent vapor annealing technology, Ostwald ripening, additive engineering and geometrically-confined lateral crystal growth) and the physical method (vapor-assisted crystal growth). Full article
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Open AccessReview Selenium-Doped Hydroxyapatite Nanocrystals–Synthesis, Physicochemical Properties and Biological Significance
Crystals 2018, 8(5), 188; https://doi.org/10.3390/cryst8050188
Received: 30 March 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
Hydroxyapatites (HAs), as materials with a similar structure to bone minerals, play a key role in biomaterials engineering. They have been applied as bone substitute materials and as coatings for metallic implants, which facilitates their osseointegration. One of the beneficial characteristics of HA,
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Hydroxyapatites (HAs), as materials with a similar structure to bone minerals, play a key role in biomaterials engineering. They have been applied as bone substitute materials and as coatings for metallic implants, which facilitates their osseointegration. One of the beneficial characteristics of HA, when used to create biocompatible materials with improved physicochemical or biological properties, is its capacity for ionic substitution. The aim of the study was to present the current state of knowledge about HAs containing selenate ions IV or VI. The enrichment of HAs with selenium aims to create a material with advantageous effects on bone tissue metabolism, as well as having anticancer and antibacterial activity. The work is devoted to both methods of obtaining Se-HA and an evaluation of its chemical structure and physicochemical properties. In addition, the biological activity of such materials in vitro and in vivo is discussed. Full article
(This article belongs to the Special Issue Crystal Structures of Compounds Containing Ions Selenite)
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Open AccessReview A Novel Approach to Modelling Nanoindentation Instabilities
Crystals 2018, 8(5), 200; https://doi.org/10.3390/cryst8050200
Received: 17 January 2018 / Revised: 25 April 2018 / Accepted: 27 April 2018 / Published: 3 May 2018
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Abstract
We review the recently developed models for load fluctuations in the displacement controlled mode and displacement jumps in the load controlled mode of indentation. To do this, we devise a method for calculating plastic contribution to load drops and displacement jumps by setting-up
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We review the recently developed models for load fluctuations in the displacement controlled mode and displacement jumps in the load controlled mode of indentation. To do this, we devise a method for calculating plastic contribution to load drops and displacement jumps by setting-up a system of coupled nonlinear time evolution equations for the mobile and forest dislocation densities by including relevant dislocation mechanisms. These equations are then coupled to the equation defining constant displacement rate or load rate. The model for the displacement controlled mode using a spherical indenter predicts all the generic features of nanoindentation such as the elastic branch followed by several force drops of decreasing magnitudes and residual indentation depth after unloading. The stress corresponding to the elastic force maximum is close to the yield stress of an ideal solid. The predicted numbers for all the quantities match experiments on single crystals of Au using a spherical indenter. We extend the approach to model the load controlled nanoindentation experiments that employ a Berkovich indenter. We first identify the dislocation mechanisms contributing to different regions of the F z curve as a first step for obtaining a good fit to a given experimental F z curve. This is done by studying the influence of the parameters associated with various dislocation mechanisms on the model F z curves. The study also demonstrates that the model predicts all the generic features of nanoindentation such as the existence of an initial elastic branch followed by several displacement jumps of decreasing magnitudes and residual plasticity after unloading for a range of model parameter values. Furthermore, an optimized set of parameter values can be easily determined that give a good fit to the experimental load–displacement curves for Al single crystals of ( 110 ) and ( 133 ) orientations. Our model also predicts the indentation size effect in a region where the displacement jumps disappear. The good agreement of the results of the models with experiments supports our view that the present approach can be used as an alternate method to simulations. The approach also provides insights into several open questions. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessReview Layered Indium Selenide under High Pressure: A Review
Crystals 2018, 8(5), 206; https://doi.org/10.3390/cryst8050206
Received: 11 April 2018 / Revised: 2 May 2018 / Accepted: 7 May 2018 / Published: 9 May 2018
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Abstract
This paper intends a short review of the research work done on the structural and electronic properties of layered Indium Selenide (InSe) and related III–VI semiconductors under high pressure conditions. The paper will mainly focus on the crucial role played by high pressure
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This paper intends a short review of the research work done on the structural and electronic properties of layered Indium Selenide (InSe) and related III–VI semiconductors under high pressure conditions. The paper will mainly focus on the crucial role played by high pressure experimental and theoretical tools to investigate the electronic structure of InSe. This objective involves a previous revision of results on the pressure dependence of the InSe crystal structure and related topics such as the equation of state and the pressure-temperature crystal phase diagram. The main part of the paper will be devoted to reviewing the literature on the optical properties of InSe under high pressure, especially the absorption experiments that led to the identification of the main optical transitions, and their assignment to specific features of the electronic structure, with the help of modern first-principles band structure calculations. In connection with these achievements we will also review relevant results on the lattice dynamical, dielectric, and transport properties of InSe, as they provided very useful supplementary information on the electronic structure of the material. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessReview Peak Broadening Anisotropy and the Contrast Factor in Metal Alloys
Crystals 2018, 8(5), 212; https://doi.org/10.3390/cryst8050212
Received: 14 March 2018 / Revised: 22 April 2018 / Accepted: 8 May 2018 / Published: 13 May 2018
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Abstract
Diffraction peak profile analysis (DPPA) is a valuable method to understand the microstructure and defects present in a crystalline material. Peak broadening anisotropy, where broadening of a diffraction peak doesn’t change smoothly with 2θ or d-spacing, is an important aspect of these
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Diffraction peak profile analysis (DPPA) is a valuable method to understand the microstructure and defects present in a crystalline material. Peak broadening anisotropy, where broadening of a diffraction peak doesn’t change smoothly with 2θ or d-spacing, is an important aspect of these methods. There are numerous approaches to take to deal with this anisotropy in metal alloys, which can be used to gain information about the dislocation types present in a sample and the amount of planar faults. However, there are problems in determining which method to use and the potential errors that can result. This is particularly the case for hexagonal close packed (HCP) alloys. There is though a distinct advantage of broadening anisotropy in that it provides a unique and potentially valuable way to develop crystal plasticity and work-hardening models. In this work we use several practical examples of the use of DPPA to highlight the issues of broadening anisotropy. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessReview Twin Domains in Organometallic Halide Perovskite Thin-Films
Crystals 2018, 8(5), 216; https://doi.org/10.3390/cryst8050216
Received: 30 March 2018 / Revised: 25 April 2018 / Accepted: 11 May 2018 / Published: 16 May 2018
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Abstract
The perovskite is a class of material with crystalline structure similar to CaTiO3. In recent years, the organic-inorganic hybrid metallic halide perovskite has been widely investigated as a promising material for a new generation photovoltaic device, whose power conversion efficiency (PCE)
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The perovskite is a class of material with crystalline structure similar to CaTiO3. In recent years, the organic-inorganic hybrid metallic halide perovskite has been widely investigated as a promising material for a new generation photovoltaic device, whose power conversion efficiency (PCE) record reaches 22.7%. One of its underlying morphological characteristics is the twin domain within those sub-micron sized crystal grains in perovskite thin films. This is important for discussion since it could be the key for understanding the fundamental mechanism of the device’s high performance, such as long diffusion distance and low recombination rate. This review aims to summarize studies on twin domains in perovskite thin films, in order to figure out its importance, guide the current studies on mechanism, and design new devices. Firstly, we introduce the research history and characteristics of widely known twin domains in inorganic perovskite BaTiO3. We then focus on the impact of the domain structure emerging in hybrid metallic halide perovskite thin films, including the observation and discussion on ferroelectricity/ferroelasity. The theoretical analysis is also presented in this review. Finally, we present a spectroscopic method, which can reveal the generality of twin domains within perovskite thin films. We anticipate that this summary on the structural and physical properties of organometallic halide perovskite will help to understand and improve the high-performance of photovoltaic devices. Full article
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Open AccessReview High-Pressure, High-Temperature Behavior of Silicon Carbide: A Review
Crystals 2018, 8(5), 217; https://doi.org/10.3390/cryst8050217
Received: 26 April 2018 / Revised: 10 May 2018 / Accepted: 11 May 2018 / Published: 16 May 2018
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Abstract
The high-pressure behavior of silicon carbide (SiC), a hard, semi-conducting material commonly known for its many polytypic structures and refractory nature, has increasingly become the subject of current research. Through work done both experimentally and computationally, many interesting aspects of high-pressure SiC have
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The high-pressure behavior of silicon carbide (SiC), a hard, semi-conducting material commonly known for its many polytypic structures and refractory nature, has increasingly become the subject of current research. Through work done both experimentally and computationally, many interesting aspects of high-pressure SiC have been measured and explored. Considerable work has been done to measure the effect of pressure on the vibrational and material properties of SiC. Additionally, the transition from the low-pressure zinc-blende B3 structure to the high-pressure rocksalt B1 structure has been measured by several groups in both the diamond-anvil cell and shock communities and predicted in numerous computational studies. Finally, high-temperature studies have explored the thermal equation of state and thermal expansion of SiC, as well as the high-pressure and high-temperature melting behavior. From high-pressure phase transitions, phonon behavior, and melting characteristics, our increased knowledge of SiC is improving our understanding of its industrial uses, as well as opening up its application to other fields such as the Earth sciences. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessReview One-Dimensional Zinc Oxide Nanomaterials for Application in High-Performance Advanced Optoelectronic Devices
Crystals 2018, 8(5), 223; https://doi.org/10.3390/cryst8050223
Received: 27 April 2018 / Revised: 13 May 2018 / Accepted: 13 May 2018 / Published: 18 May 2018
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Abstract
Unlike conventional bulk or film materials, one-dimensional (1D) semiconducting zinc oxide (ZnO) nanostructures exhibit excellent photoelectric properties including ultrahigh intrinsic photoelectric gain, multiple light confinement, and subwavelength size effects. Compared with polycrystalline thin films, nanowires usually have high phase purity, no grain boundaries,
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Unlike conventional bulk or film materials, one-dimensional (1D) semiconducting zinc oxide (ZnO) nanostructures exhibit excellent photoelectric properties including ultrahigh intrinsic photoelectric gain, multiple light confinement, and subwavelength size effects. Compared with polycrystalline thin films, nanowires usually have high phase purity, no grain boundaries, and long-distance order, making them attractive for carrier transport in advanced optoelectronic devices. The properties of one-dimensional nanowires—such as strong optical absorption, light emission, and photoconductive gain—could improve the performance of light-emitting diodes (LEDs), photodetectors, solar cells, nanogenerators, field-effect transistors, and sensors. For example, ZnO nanowires behave as carrier transport channels in photoelectric devices, decreasing the loss of the light-generated carrier. The performance of LEDs and photoelectric detectors based on nanowires can be improved compared with that of devices based on polycrystalline thin films. This article reviews the fabrication methods of 1D ZnO nanostructures—including chemical vapor deposition, hydrothermal reaction, and electrochemical deposition—and the influence of the growth parameters on the growth rate and morphology. Important applications of 1D ZnO nanostructures in optoelectronic devices are described. Several approaches to improve the performance of 1D ZnO-based devices, including surface passivation, localized surface plasmons, and the piezo-phototronic effect, are summarized. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessReview The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds
Crystals 2018, 8(5), 225; https://doi.org/10.3390/cryst8050225
Received: 25 April 2018 / Revised: 13 May 2018 / Accepted: 14 May 2018 / Published: 18 May 2018
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Abstract
Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the
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Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the Crystal Orbital Hamilton Population (COHP) method has been established as an efficient and reliable tool to extract the chemical-bonding information based on electronic-structure calculations of various quantum-chemical types. In this review, we present a brief introduction into the theoretical background of the COHP method and illustrate the latter by diverse applications, in particular by looking at representatives of the class of (polar) intermetallic compounds, usually considered as “black sheep” in the light of valence-electron counting schemes. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)
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Open AccessReview Brief Review of Surface Passivation on III-V Semiconductor
Crystals 2018, 8(5), 226; https://doi.org/10.3390/cryst8050226
Received: 30 March 2018 / Revised: 4 May 2018 / Accepted: 9 May 2018 / Published: 18 May 2018
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Abstract
The III-V compound semiconductor, which has the advantage of wide bandgap and high electron mobility, has attracted increasing interest in the optoelectronics and microelectronics field. The poor electronic properties of III-V semiconductor surfaces resulting from a high density of surface/interface states limit III-V
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The III-V compound semiconductor, which has the advantage of wide bandgap and high electron mobility, has attracted increasing interest in the optoelectronics and microelectronics field. The poor electronic properties of III-V semiconductor surfaces resulting from a high density of surface/interface states limit III-V device technology development. Various techniques have been applied to improve the surface and interface quality, which cover sulfur-passivation, plasmas-passivation, ultrathin film deposition, and so on. In this paper, recent research of the surface passivation on III-V semiconductors was reviewed and compared. It was shown that several passivation methods can lead to a perfectly clean surface, but only a few methods can be considered for actual device integration due to their effectiveness and simplicity. Full article
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