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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 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 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
[...] Read more.
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 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 (
[...] Read more.
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 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 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
[...] Read more.
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 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
[...] Read more.
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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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
[...] Read more.
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 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
[...] Read more.
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 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,
[...] Read more.
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 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 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 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 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 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 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 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)
[...] Read more.
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 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
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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 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
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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 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 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 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 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
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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 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 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 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
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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 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 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 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 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 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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