Crystals

11 pages, 2573 KiB

Open AccessCommunication

Synthesis and Fluorescence Properties of Asymmetrical Salamo-Type Tetranuclear Zinc(II) Complex

by Yun-Dong Peng, Xiao-Yan Li, Quan-Peng Kang, Gao-Xian An, Yang Zhang and Wen-Kui Dong

Crystals 2018, 8(2), 107; https://doi.org/10.3390/cryst8020107 - 24 Feb 2018

Cited by 45 | Viewed by 3910

A new tetranuclear zinc(II) complex with an asymmetrical Salamo-type chelating ligand, H₃L (5-methoxy-6′-hydroxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), was synthesized and characterized using FT-IR, elemental analyses, X-ray single crystal diffraction method, UV-Vis, and fluorescence spectra. The zinc(II) complex possesses the cell parameters a = 8.1960(7) Å, [...] Read more.

A new tetranuclear zinc(II) complex with an asymmetrical Salamo-type chelating ligand, H₃L (5-methoxy-6′-hydroxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol), was synthesized and characterized using FT-IR, elemental analyses, X-ray single crystal diffraction method, UV-Vis, and fluorescence spectra. The zinc(II) complex possesses the cell parameters a = 8.1960(7) Å, b = 9.8127(8) Å, c = 16.5428(15) Å, Z = 1, V = 1172.5(2) Å³, R₁ = 0.0722, and wR₂ = 0.1558, and crystallizes in the triclinic system, with space group P-1. X-ray crystal structure analysis reveals that Zn1 and Zn2 atoms are all pentacoordinated and adopt slightly twisted tetragonal pyramidal and trigonal bipyramidal geometries. The zinc(II) complex forms a 1D supramolecular chain via intermolecular hydrogen bonds along the b axis. Besides, the fluorescence properties have been discussed. Full article

(This article belongs to the Section Crystal Engineering)

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28 pages, 7765 KiB

Open AccessReview

The Effects of Nanostructure on the Hydrogen Sorption Properties of Magnesium-Based Metallic Compounds: A Review

by Luca Pasquini

Crystals 2018, 8(2), 106; https://doi.org/10.3390/cryst8020106 - 23 Feb 2018

Cited by 37 | Viewed by 5695

Abstract

In this review, I examine the influence of nanoscale materials features on the hydrogen-metal interaction. The small system size, the abundance of surfaces/interfaces, and the spatial distribution of phases are the key factors to understand the hydrogen sorption properties of nanomaterials. In order [...] Read more.

In this review, I examine the influence of nanoscale materials features on the hydrogen-metal interaction. The small system size, the abundance of surfaces/interfaces, and the spatial distribution of phases are the key factors to understand the hydrogen sorption properties of nanomaterials. In order to describe nanoscale-specific thermodynamic changes, I present a quantitative model applicable to every hydride-forming material, independently on its composition and atomic structure. The effects of surface free energy, interface free energy, and elastic constraint, are included in a general expression for the thermodynamical bias. In the frame of this model, I critically survey theoretical and experimental results hinting at possible changes of thermodynamic parameters, and in particular, enthalpy and entropy of hydride formation, in nanostructured Mg-based metallic compounds as compared to their coarse-grained bulk counterparts. I discuss the still open controversies, such as destabilization of ultra-small clusters and enthalpy–entropy compensation. I also highlight the frequently missed points in experiments and data interpretation, such as the importance of recording full hydrogen absorption and desorption isotherms and of measuring the hysteresis. Finally, I try to address the open questions that may inspire future research, with the ambition of tailoring the properties of hydride nanomaterials through a deeper understanding of their thermodynamics. Full article

(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)

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12 pages, 5292 KiB

Open AccessArticle

Mechanically Robust 3D Graphene–Hydroxyapatite Hybrid Bioscaffolds with Enhanced Osteoconductive and Biocompatible Performance

by Weibo Xie, Fuxiang Song, Rui Wang, Shenglin Sun, Miao Li, Zengjie Fan, Bin Liu, Qiangqiang Zhang and Jizeng Wang

Crystals 2018, 8(2), 105; https://doi.org/10.3390/cryst8020105 - 23 Feb 2018

Cited by 20 | Viewed by 4449

Abstract

In this paper, we describe three-dimensional (3D) hierarchical graphene–hydroxyapatite hybrid bioscaffolds (GHBs) with a calcium phosphate salt electrochemically deposited onto the framework of graphene foam (GF). The morphology of the hydroxyapatite (HA) coverage over GF was controlled by the deposition conditions, including temperature [...] Read more.

In this paper, we describe three-dimensional (3D) hierarchical graphene–hydroxyapatite hybrid bioscaffolds (GHBs) with a calcium phosphate salt electrochemically deposited onto the framework of graphene foam (GF). The morphology of the hydroxyapatite (HA) coverage over GF was controlled by the deposition conditions, including temperature and voltage. The HA obtained at the higher temperature demonstrates the more uniformly distributed crystal grain with the smaller size. The as-prepared GHBs show a high elasticity with recoverable compressive strain up to 80%, and significantly enhanced strength with Young’s modulus up to 0.933 MPa compared with that of pure GF template (~7.5 kPa). Moreover, co-culture with MC3T3-E1 cells reveals that the GHBs can more effectively promote the proliferation of MC3T3-E1 osteoblasts with good biocompatibility than pure GF and the control group. The superior performance of GHBs suggests their promising applications as multifunctional materials for the repair and regeneration of bone defects. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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10 pages, 17514 KiB

Open AccessArticle

One Step Preparation of Fe–FeO–Graphene Nanocomposite through Pulsed Wire Discharge

by Xin Gao, Naoaki Yokota, Hayato Oda, Shigeru Tanaka, Kazuyuki Hokamoto and Pengwan Chen

Crystals 2018, 8(2), 104; https://doi.org/10.3390/cryst8020104 - 23 Feb 2018

Cited by 29 | Viewed by 6985

Abstract

The Fe–FeO–graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded [...] Read more.

The Fe–FeO–graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded to analyze the process of the pulsed wire discharge. The as-prepared samples—under different charging voltages—were recovered and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM). Curved and loose graphene films that were anchored with spherical Fe and FeO nanoparticles were obtained at the charging voltage of 8–10 kV. The present study discusses the mechanism by which the Fe–FeO–graphene nanocomposite material was formed during the pulsed wire discharge process. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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9 pages, 3797 KiB

Open AccessFeature PaperArticle

Synthesis, Crystal Structure Analysis and Decomposition of RbAlH₄

by Claudia Weidenthaler, Michael Felderhoff, Thomas Bernert, Magnus H. Sørby, Bjørn C. Hauback and Daniel Krech

Crystals 2018, 8(2), 103; https://doi.org/10.3390/cryst8020103 - 22 Feb 2018

Cited by 4 | Viewed by 4539

Abstract

RbAlH₄, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The [...] Read more.

RbAlH₄, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The structure refinement of neutron diffraction data confirms that RbAlD₄ is isostructural to KAlD₄. The decomposition proceeds via two distinct processes at temperatures above 275 °C. However, the structures formed during decomposition seem to be different from the compounds formed during hydrogen release of early alkali metal aluminum hydrides. Full article

(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)

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10 pages, 1786 KiB

Open AccessArticle

Atomic-Site-Specific Analysis on Out-of-Plane Elasticity of Convexly Curved Graphene and Its Relationship to s p 2 to s p 3 Re-Hybridization

by Makoto Ashino and Roland Wiesendanger

Crystals 2018, 8(2), 102; https://doi.org/10.3390/cryst8020102 - 20 Feb 2018

Cited by 4 | Viewed by 4067

Abstract

The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties [...] Read more.

The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties of graphene under compressing and stretching deformations have been exclusively investigated by local-probe techniques. Here we report that the interatomic attractive force introduced by atomic force microscopy triggers “single”-atom displacement and consequently enables us to determine out-of-plane elasticities of convexly curved graphene including its atomic-site-specific variation. We have quantitatively evaluated the relationship between the out-of-plane displacement and elasticity of convexly curved graphene by three-dimensional force field spectroscopy on a side-wall of a hollow tube with a well-defined curvature. The substantially small intrinsic modulus that complies with continuum mechanics has been found to increase significantly at atomically specific locations, where

s p^{2}

to

s p^{3}

re-hybridization would certainly take place. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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39 pages, 23020 KiB

Open AccessReview

Drug‑Drug and Drug‑Nutraceutical Cocrystal/Salt as Alternative Medicine for Combination Therapy: A Crystal Engineering Approach

by Ranjit Thakuria and Bipul Sarma

Crystals 2018, 8(2), 101; https://doi.org/10.3390/cryst8020101 - 18 Feb 2018

Cited by 122 | Viewed by 23722

Abstract

The pre-formulation of pharmaceutical cocrystals and salts is a concept of crystal engineering that has emerged as a promising technique for drug development in pharmaceutical industry. Recent introduction of pharmaceutical cocrystals in regulatory guidelines of US Food and Drug Administration (FDA) made them [...] Read more.

The pre-formulation of pharmaceutical cocrystals and salts is a concept of crystal engineering that has emerged as a promising technique for drug development in pharmaceutical industry. Recent introduction of pharmaceutical cocrystals in regulatory guidelines of US Food and Drug Administration (FDA) made them one of the potential alternatives when salt preparation is not feasible. Apart from generally regarded as safe (GRAS) coformers, drug‑drug and drug‑nutraceutical cocrystals are recent additions to pharmaceutical cocrystal family that have additional health benefits. Indeed, preparation of salt forms is a routine practice to deal with inadequacies associated with the active pharmaceutical ingredient (API) and happens to be a potentially reliable method. Amongst them, drug-drug and drug-nutraceutical cocrystals have drawn significant importance in the recent past as they reduce drug load and cost effects during multiple disease diagnosis. However, one has to be prudent in the selection of drug molecules, the presence of complementary hydrogen bond synthon, disease management during multiple disease therapy, etc. that play important roles in their preparation. That is the reason why drug–drug cocrystals are scarce in the literature compared to pharmaceutical cocrystals containing GRAS coformers and salt forms. Herein, we discuss case studies preferably the reported drug‑drug, drug‑nutraceutical cocrystals, and a few salts with an emphasis on their role in physicochemical property modulation. Full article

(This article belongs to the Special Issue Novel Pharmaceutical Cocrystals and Their Applications)

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11 pages, 9195 KiB

Open AccessArticle

Incorporation of Hexanuclear Mn(II,III) Carboxylate Clusters with a {Mn₆O₂} Core in Polymeric Structures

by Mariana Darii, Irina G. Filippova, Jürg Hauser, Silvio Decurtins, Shi-Xia Liu, Victor Ch. Kravtsov and Svetlana G. Baca

Crystals 2018, 8(2), 100; https://doi.org/10.3390/cryst8020100 - 17 Feb 2018

Cited by 3 | Viewed by 4195

Abstract

A new series of hexanuclear mixed-valent carboxylate coordination clusters of the type [Mn6O2(O2CR)10L4] (R = CMe3; CHMe2) featuring a {MnII4MnIII2(μ4-O)2} core of composition [Mn6O2(O2CCMe3)10(Me3CCO2H)3(EtOH)]•(Me3CCO2H) (1), [Mn6O2(O2CCMe3)10(Me3CCO2H)2 (EtOH)2]•2(EtOH) (2) and [Mn6O2(O2CCMe3)10(Me3CCO2H)2(MeOH)2]•2(MeOH)•H2O (3), and coordination polymers which incorporate such clusters, namely [Mn6O2(O2CCHMe2)10(pyz)(MeOH)2]n (4), {[Mn6O2(O2CCHMe2)10(pyz)1.5(H2O)]•0.5(H2O)}n (5), [...] Read more.

A new series of hexanuclear mixed-valent carboxylate coordination clusters of the type [Mn6O2(O2CR)10L4] (R = CMe3; CHMe2) featuring a {MnII4MnIII2(μ4-O)2} core of composition [Mn6O2(O2CCMe3)10(Me3CCO2H)3(EtOH)]•(Me3CCO2H) (1), [Mn6O2(O2CCMe3)10(Me3CCO2H)2 (EtOH)2]•2(EtOH) (2) and [Mn6O2(O2CCMe3)10(Me3CCO2H)2(MeOH)2]•2(MeOH)•H2O (3), and coordination polymers which incorporate such clusters, namely [Mn6O2(O2CCHMe2)10(pyz)(MeOH)2]n (4), {[Mn6O2(O2CCHMe2)10(pyz)1.5(H2O)]•0.5(H2O)}n (5), and [Mn6O2(O2CCMe3)10(HO2CCMe3)2(en)]n (6), have been synthesized (where pyz = pyrazine, en = ethyl nicotinate). The modification of the cluster surface by a diverse combination of capped or bridging ligands attached to peripheral MnII atoms results in discrete clusters with a closed hydrophobic exterior shell in 1 and 2, supramolecular chains built through hydrogen bonded solvent molecule clusters in 3, linear coordination polymers in 4 and 6 or a ladder-like coordination polymer in 5. The H-bonded coordination polymers 4 and 5 form supramolecular layers in crystals. Full article

(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)

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11 pages, 3234 KiB

Open AccessArticle

Atomic Charges and Chemical Bonding in Y-Ga Compounds

by Yuri Grin, Anatolij Fedorchuk, Rodolfo J. Faria and Frank R. Wagner

Crystals 2018, 8(2), 99; https://doi.org/10.3390/cryst8020099 - 16 Feb 2018

Cited by 14 | Viewed by 4504

Abstract

A negative deviation from Vegard rule for the average atomic volume versus yttrium content was found from experimental crystallographic information about the binary compounds of yttrium with gallium. Analysis of the electron density (DFT calculations) employing the quantum theory of atoms in molecules [...] Read more.

A negative deviation from Vegard rule for the average atomic volume versus yttrium content was found from experimental crystallographic information about the binary compounds of yttrium with gallium. Analysis of the electron density (DFT calculations) employing the quantum theory of atoms in molecules revealed an increase in the atomic volumes of both Y and Ga with the increase in yttrium content. The non-linear increase is caused by the strengthening of covalent Y-Ga interactions with stronger participation of genuine penultimate shell electrons (4d electrons of yttrium) in the valence region. Summing the calculated individual atomic volumes for a unit cell allows understanding of the experimental trend. With increasing yttrium content, the polarity of the Y-Ga bonding and, thus its ionicity, rises. The covalency of the atomic interactions in Y-Ga compounds is consistent with their delocalization from two-center to multi-center ones. Full article

(This article belongs to the Special Issue Experimental and Theoretical Electron Density Analysis of Crystals)

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8 pages, 7425 KiB

Open AccessArticle

The Electrical Properties of Tb-Doped CaF₂ Nanoparticles under High Pressure

by Tingjing Hu, Xiaoyan Cui, Jingshu Wang, Xin Zhong, Yinzhu Chen, Junkai Zhang, Xuefei Li, Jinghai Yang and Chunxiao Gao

Crystals 2018, 8(2), 98; https://doi.org/10.3390/cryst8020098 - 15 Feb 2018

Cited by 8 | Viewed by 4076

Abstract

The high-pressure transport behavior of CaF₂ nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca²⁺ by Tb [...] Read more.

The high-pressure transport behavior of CaF₂ nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca²⁺ by Tb³⁺ leads to deformation in the lattice, and finally lowers the transition pressure. The F⁻ ions diffusion, electronic transport, and charge-discharge process become more difficult with the rising pressure. In the electronic transport process, defects at grains play a dominant role. The charge carriers include both F⁻ ions and electrons, and electrons are dominant in the transport process. The Tb doping improves the pressure effect on the transport behavior of CaF₂ nanocrystals. Full article

(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)

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8 pages, 2105 KiB

Open AccessArticle

Crystal Structure of Shigella flexneri SF173 Reveals a Dimeric Helical Bundle Conformation

by Ji-Hun Kim, Hyung-Sik Won, Won-Su Yoon, Seung-Hyeon Seok, Bong-Jun Jung, Seu-Na Lee, Dae-Won Sim and Min-Duk Seo

Crystals 2018, 8(2), 97; https://doi.org/10.3390/cryst8020097 - 14 Feb 2018

Cited by 1 | Viewed by 3868

Abstract

We report the crystal structure and bioinformatic analysis of SF173, a functionally uncharacterized protein from the human enteropathogenic bacteria Shigella flexneri. The structure shows a tightly interlinked dimer formed by adimeric core comprising α2 and α3 helices from both subunits and swapping [...] Read more.

We report the crystal structure and bioinformatic analysis of SF173, a functionally uncharacterized protein from the human enteropathogenic bacteria Shigella flexneri. The structure shows a tightly interlinked dimer formed by adimeric core comprising α2 and α3 helices from both subunits and swapping the N-terminal α1 helix of each monomer. Structural inspection and genomic analysis results suggest that the SF173 might play its putative function by binding to SF172, the partially overlapped upstream product in the operon. As YaeO (an SF172 orthologue) has been identified to be an inhibitor of the bacterial transcription terminator Rho protein, SF173 is suggested to be involved in the regulation of Rho-dependent transcription termination, by inhibiting the Rho protein binding to SF172/YaeO. Full article

(This article belongs to the Special Issue Recent Advances in Protein Crystallography)

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18 pages, 599 KiB

Open AccessArticle

Effects of Alloying Atoms on Antiphase Boundary Energy and Yield Stress Anomaly of L1₂ Intermetallics: First-Principles Study

by Xiaojun Gao, Jianwei Wang, Xiaozhi Wu, Rui Wang and Zhihong Jia

Crystals 2018, 8(2), 96; https://doi.org/10.3390/cryst8020096 - 12 Feb 2018

Cited by 10 | Viewed by 5341

Abstract

The antiphase boundary energies of {111} and {010} planes in L1

_{2}

intermetallics (Ni

_{3}

Ge, Ni

_{3}

Si, Al

_{3}

Sc, Ni

_{3}

Al, Ni

_{3}

Ga and Al

_{3}

Ti) under different pressure are presented using first-principle methods. The yield stress [...] Read more.

The antiphase boundary energies of {111} and {010} planes in L1

_{2}

intermetallics (Ni

_{3}

Ge, Ni

_{3}

Si, Al

_{3}

Sc, Ni

_{3}

Al, Ni

_{3}

Ga and Al

_{3}

Ti) under different pressure are presented using first-principle methods. The yield stress anomaly is predicted by the energy criterion p-factor based on the anisotropy of antiphase boundary energies and elasticity. These L1

_{2}

intermetallics exhibit anomalous yield stress behavior except Al

_{3}

Sc. It is found that pressure cannot introduce the transition between anomalous and normal behavior. In order to investigate the transition, Al

_{3}

Sc, Ni

_{3}

Si and Ni

_{3}

Ge with substituting atoms are investigated in detail due to p-factors of them are close to the critical value

p_{c} = \sqrt{3}

. Al

_{3}

Sc can change to anomalous when Sc atoms in {010} planes are substituted by Ti with plane concentration 25%. When Li substitutes Al in {111} planes, anomalous Al

_{3}

Sc will change to normal. Ni

_{3}

Si and Ni

_{3}

Ge can exhibit normal yield stress behavior when Ge and Si in {111} planes are substituted by alloying atoms with plane concentrations 12.5% and 25%. When Ga and Al substitute in {010} planes, normal Ni

_{3}

Si and Ni

_{3}

Ge will revert to anomalous behavior. Therefore, transparent transition between normal and anomalous yield stress behavior in L1

_{2}

intermetallics can be introduced by alloying atoms. Full article

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9 pages, 3969 KiB

Open AccessArticle

Ultra-Wide-Bandwidth Tunable Magnetic Fluid-Filled Hybrid Connected Dual-Core Photonic Crystal Fiber Mode Converter

by Yingying Yu and Bo Sun

Crystals 2018, 8(2), 95; https://doi.org/10.3390/cryst8020095 - 12 Feb 2018

Cited by 11 | Viewed by 3732

Abstract

We propose a tunable magnetic fluid-filled hybrid photonic crystal fiber mode converter. Innovative design principles based on the hybrid connected dual-core photonic crystal fiber and magnetically modulated optical properties of magnetic fluid are developed and numerically verified. The mode converter was designed to [...] Read more.

We propose a tunable magnetic fluid-filled hybrid photonic crystal fiber mode converter. Innovative design principles based on the hybrid connected dual-core photonic crystal fiber and magnetically modulated optical properties of magnetic fluid are developed and numerically verified. The mode converter was designed to convert LP₁₁ in the index-guiding core to the LP₀₁ mode in the photonic bandgap-guiding core. By introducing the magnetic fluid into the air-hole located at the center of the photonic bandgap-guiding core, the mode converter can realize a high coupling efficiency and an ultra-wide bandwidth. The coupling efficiency can reach up to 99.9%. At a fixed fiber length, by adjusting the strength of the magnetic field, the coupling efficiency can reach up to 90% and 95% at wavelengths in the ranges of 1.33 µm–1.85 µm and 1.38 µm–1.75 µm, with bandwidth values reaching 0.52 µm and 0.37 µm, respectively. Moreover, it has a good manufacturing flexibility. The mode converter can be used to implement wideband mode-division multiplexing of few-mode optical fiber for high-capacity telecommunications. Full article

(This article belongs to the Special Issue Photonic Crystal Fiber)

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12 pages, 1419 KiB

Open AccessArticle

Mg₂FeH₆ Synthesis Efficiency Map

by Katarzyna Witek, Krzysztof Karczewski, Magdalena Karpowicz and Marek Polanski

Crystals 2018, 8(2), 94; https://doi.org/10.3390/cryst8020094 - 11 Feb 2018

Cited by 19 | Viewed by 4604

Abstract

The influences of the processing parameters on the Mg₂FeH₆ synthesis yield were studied. Mixtures of magnesium hydride (MgH₂) and iron (Fe) were mechanically milled in a planetary ball mill under argon for 0.5-, 1-, 2- and 3-h periods [...] Read more.

The influences of the processing parameters on the Mg₂FeH₆ synthesis yield were studied. Mixtures of magnesium hydride (MgH₂) and iron (Fe) were mechanically milled in a planetary ball mill under argon for 0.5-, 1-, 2- and 3-h periods and subsequently sintered at temperatures from 300–500

^{\circ}

C under hydrogen. The reaction yield, phase content and hydrogen storage properties of the received materials were investigated. The morphologies of the powders after synthesis were studied by SEM. The synthesis effectiveness map was presented. The obtained results prove that synthesis parameters, such as the milling time and synthesis temperature, greatly influence the reaction yield and material properties and show that extended mechanical milling may not be beneficial to the reaction efficiency. Full article

(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)

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17 pages, 4648 KiB

Open AccessArticle

First-Principles Investigations of the Structural, Anisotropic Mechanical, Thermodynamic and Electronic Properties of the AlNi₂Ti Compound

by Shuli Tang, Yefei Li, Yimin Gao, Qiaoling Zheng, Zhiwei Liu and Xiangyi Ren

Crystals 2018, 8(2), 93; https://doi.org/10.3390/cryst8020093 - 11 Feb 2018

Cited by 15 | Viewed by 5426

Abstract

In this paper, the electronic, mechanical and thermodynamic properties of AlNi₂Ti are studied by first-principles calculations in order to reveal the influence of AlNi₂Ti as an interfacial phase on ZTA (zirconia toughened alumina)/Fe. The results show that AlNi₂ [...] Read more.

In this paper, the electronic, mechanical and thermodynamic properties of AlNi₂Ti are studied by first-principles calculations in order to reveal the influence of AlNi₂Ti as an interfacial phase on ZTA (zirconia toughened alumina)/Fe. The results show that AlNi₂Ti has relatively high mechanical properties, which will benefit the impact or wear resistance of the ZTA/Fe composite. The values of bulk, shear and Young’s modulus are 164.2, 63.2 and 168.1 GPa respectively, and the hardness of AlNi₂Ti (4.4 GPa) is comparable to common ferrous materials. The intrinsic ductile nature and strong metallic bonding character of AlNi₂Ti are confirmed by B/G and Poisson’s ratio. AlNi₂Ti shows isotropy bulk modulus and anisotropic elasticity in different crystallographic directions. At room temperature, the linear thermal expansion coefficient (LTEC) of AlNi₂Ti estimated by quasi-harmonic approximation (QHA) based on Debye model is 10.6 × 10⁻⁶ K⁻¹, close to LTECs of zirconia toughened alumina and iron. Therefore, the thermal matching of ZTA/Fe composite with AlNi₂Ti interfacial phase can be improved. Other thermodynamic properties including Debye temperature, sound velocity, thermal conductivity and heat capacity, as well as electronic properties, are also calculated. Full article

(This article belongs to the Special Issue Crystal Structure of Magnetic Materials)

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14 pages, 8192 KiB

Open AccessArticle

Specific Structural Disorder in an Anion Layer and Its Influence on Conducting Properties of New Crystals of the (BEDT-TTF)₄A⁺[M³⁺(ox)₃]G Family, Where G Is 2-Halopyridine; M Is Cr, Ga; A⁺ Is [K_0.8(H₃O)_0.2]⁺

by Tatiana G. Prokhorova, Eduard B. Yagubskii, Leokadiya V. Zorina, Sergey V. Simonov, Vladimir N. Zverev, Rimma P. Shibaeva and Lev I. Buravov

Crystals 2018, 8(2), 92; https://doi.org/10.3390/cryst8020092 - 10 Feb 2018

Cited by 13 | Viewed by 4476

Abstract

New crystals (1–4) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A⁺[M³⁺(ox)₃]³⁻G}²⁻, where M is Cr, Ga; G [...] Read more.

New crystals (1–4) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A⁺[M³⁺(ox)₃]³⁻G}²⁻, where M is Cr, Ga; G is 2-chloropyridine, 2-bromopyridine; and A⁺ is [K_0.8(H₃O)_0.2]⁺ have been prepared and their crystal structure and transport properties were studied. All crystals belong to the monoclinic group of the (BEDT-TTF)₄A⁺[M³⁺(ox)₃]G family with β″-packing type of conducting BEDT-TTF layers. In contrast to the known superconducting crystals with M³⁺ = Fe³⁺ and G = 2-chloro- or 2-bromopyridine (T_c = 4.0–4.3 K), crystals with Cr³⁺ and Ga³⁺ ions exhibit metallic properties down to 0.5 K without superconducting transition. Upon cooling these crystals, the incommensurate superstructure appears, which has never been observed before in the numerous β″-salts of the family. In addition, orthorhombic (sp. group Pbca) semiconducting crystals α″-(BEDT-TTF)₅[Ga(ox)₃]·3.4·H₂O·0.6 EtOH (5) were obtained. It is a new compound in the family of BEDT-TTF crystals with tris(oxalato)metallate anions. Full article

(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)

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10 pages, 2347 KiB

Open AccessArticle

Temperature-Induced Reversible and Irreversible Transitions between Metastable Perovskite Phases in the BiFe_1−ySc_yO₃ Solid Solutions

by Andrei N. Salak, Dmitry D. Khalyavin, Edwin Eardley, Nikolai M. Olekhnovich, Anatoli V. Pushkarev, Yury V. Radyush, Aleksandr D. Shilin and Vasili V. Rubanik

Crystals 2018, 8(2), 91; https://doi.org/10.3390/cryst8020091 - 10 Feb 2018

Cited by 3 | Viewed by 3436

Abstract

The antipolar orthorhombic Pnma phase with the

\sqrt{2} a_{p} \times 4 a_{p} \times 2 \sqrt{2} a_{p}

superstructure (a_p ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO₃. Temperature-induced [...] Read more.

The antipolar orthorhombic Pnma phase with the

\sqrt{2} a_{p} \times 4 a_{p} \times 2 \sqrt{2} a_{p}

superstructure (a_p ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO₃. Temperature-induced structural transformations in metastable perovskite solid solutions with the Pnma structure corresponding to the range of 0.30 ≤ y ≤ 0.60 of the (1−y)BiFeO₃-yBiScO₃ quasi binary system were studied using temperature X-ray and neutron powder diffraction. These compositions cannot be prepared in bulk form at ambient pressure but can be stabilized in the Pnma phase by means of quenching after synthesis under high pressure. The compositions were investigated in situ between 1.5 K and the temperature of the stability limit of their metastable phases (about 870–920 K). It has been found that heating the as-prepared compositions with the Pnma phase leads to formation of the rhombohedral R3c phase (

\sqrt{2} a_{p} \times \sqrt{2} a_{p} \times 2 \sqrt{3} a_{p}

), which, on cooling down to room temperature, either remains or transforms into a polar orthorhombic Ima2 phase (

2 a_{p} \times \sqrt{2} a_{p} \times \sqrt{2} a_{p}

). The observed phase transformations in the BiFe_1−ySc_yO₃ perovskite series on heating and on cooling are considered in terms of geometrical factors. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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12 pages, 2544 KiB

Open AccessArticle

Reactive Hydride Composite of Mg₂NiH₄ with Borohydrides Eutectic Mixtures

by Erika M. Dematteis, Silvère Vaunois, Claudio Pistidda, Martin Dornheim and Marcello Baricco

Crystals 2018, 8(2), 90; https://doi.org/10.3390/cryst8020090 - 10 Feb 2018

Cited by 16 | Viewed by 5290

Abstract

The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH [...] Read more.

The development of materials showing hydrogen sorption reactions close to room temperature and ambient pressure will promote the use of hydrogen as energy carrier for mobile and stationary large-scale applications. In the present study, in order to reduce the thermodynamic stability of MgH₂, Ni has been added to form Mg₂NiH₄, which has been mixed with various borohydrides to further tune hydrogen release reactions. De-hydrogenation/re-hydrogenation properties of Mg₂NiH₄-LiBH₄-M(BH₄)_x (M = Na, K, Mg, Ca) systems have been investigated. Mixtures of borohydrides have been selected to form eutectics, which provide a liquid phase at low temperatures, from 110 °C up to 216 °C. The presence of a liquid borohydride phase decreases the temperature of hydrogen release of Mg₂NiH₄ but only slight differences have been detected by changing the borohydrides in the eutectic mixture. Full article

(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)

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9 pages, 1831 KiB

Open AccessArticle

Crystal Structural Determination of SrAlD₅ with Corner-Sharing AlD₆ Octahedron Chains by X-ray and Neutron Diffraction

by Toyoto Sato, Shigeyuki Takagi, Magnus H. Sørby, Stefano Deledda, Bjørn C. Hauback and Shin-ichi Orimo

Crystals 2018, 8(2), 89; https://doi.org/10.3390/cryst8020089 - 9 Feb 2018

Cited by 5 | Viewed by 3949

Abstract

Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH₄]⁻ or [AlH₆]³⁻ with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions [...] Read more.

Aluminium-based complex hydrides (alanates) composed of metal cation(s) and complex anion(s), [AlH₄]⁻ or [AlH₆]³⁻ with covalent Al–H bonds, have attracted tremendous attention as hydrogen storage materials since the discovery of the reversible hydrogen desorption and absorption reactions on Ti-enhanced NaAlH₄. In cases wherein alkaline-earth metals (M) are used as a metal cation, MAlH₅ with corner-sharing AlH₆ octahedron chains are known to form. The crystal structure of SrAlH₅ has remained unsolved although two different results have been theoretically and experimentally proposed. Focusing on the corner-sharing AlH₆ octahedron chains as a unique feature of the alkaline-earth metal, we here report the crystal structure of SrAlD₅ investigated by synchrotron radiation powder X-ray and neutron diffraction. SrAlD₅ was elucidated to adopt an orthorhombic unit cell with a = 4.6226(10) Å, b = 12.6213(30) Å and c = 5.0321(10) Å in the space group Pbcm (No. 57) and Z = 4. The Al–D distances (1.77–1.81 Å) in the corner-sharing AlD₆ octahedra matched with those in the isolated [AlD₆]³⁻ although the D–Al–D angles in the penta-alanates are significantly more distorted than the isolated [AlD₆]³⁻. Full article

(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)

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10 pages, 5612 KiB

Open AccessArticle

Coupling between Spin and Charge Order Driven by Magnetic Field in Triangular Ising System LuFe₂O_4+δ

by Lei Ding, Fabio Orlandi, Dmitry D. Khalyavin, Andrew T. Boothroyd, Dharmalingam Prabhakaran, Geetha Balakrishnan and Pascal Manuel

Crystals 2018, 8(2), 88; https://doi.org/10.3390/cryst8020088 - 6 Feb 2018

Cited by 4 | Viewed by 5517

Abstract

We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe₂O_4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel [...] Read more.

We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe₂O_4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel temperature (T_N = 240 K) indicates that LuFe₂O_4+δ shows short-range, two-dimensional (2D) correlations in the FeO₅ triangular layers, characterized by the development of a magnetic scattering rod along the 1/3 1/3 L direction, persisting down to 5 K. We also found that on top of the 2D correlations, a long range ferromagnetic component associated with the propagation vector k₁ = 0 sets in at around 240 K. On the other hand, an external magnetic field applied along the c-axis effectively favours a three-dimensional (3D) spin correlation between the FeO₅ bilayers evidenced by the increase of the intensity of satellite reflections with propagation vector k₂ = (1/3, 1/3, 3/2). This magnetic modulation is identical to the charge ordered superstructure, highlighting the field-promoted coupling between the spin and charge degrees of freedom. Formation of the 3D spin correlations suppresses both the rod-type diffuse scattering and the k₁ component. Simple symmetry-based arguments provide a natural explanation of the observed phenomenon and put forward a possible charge redistribution in the applied magnetic field. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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10 pages, 1559 KiB

Open AccessArticle

Low-Temperature Lattice Effects in the Spin-Liquid Candidate κ-(BEDT-TTF)₂Cu₂(CN)₃

by Rudra Sekhar Manna, Steffi Hartmann, Elena Gati, John A. Schlueter, Mariano De Souza and Michael Lang

Crystals 2018, 8(2), 87; https://doi.org/10.3390/cryst8020087 - 6 Feb 2018

Cited by 13 | Viewed by 5535

Abstract

The quasi-two-dimensional organic charge-transfer salt

κ

-(BEDT-TTF)

_{2}

Cu

_{2}

(CN)

_{3}

is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive [...] Read more.

The quasi-two-dimensional organic charge-transfer salt

κ

-(BEDT-TTF)

_{2}

Cu

_{2}

(CN)

_{3}

is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive investigations of the material’s low-temperature properties, several important questions remain to be answered. Particularly puzzling are the 6 K anomaly and the enigmatic effects observed in magnetic fields. Here we report on low-temperature measurements of lattice effects which were shown to be particularly strongly pronounced in this material (R. S. Manna et al., Phys. Rev. Lett. 2010, 104, 016403)). A special focus of our study lies on sample-to-sample variations of these effects and their implications on the interpretation of experimental data. By investigating overall nine single crystals from two different batches, we can state that there are considerable differences in the size of the second-order phase transition anomaly around 6 K, varying within a factor of 3. In addition, we find field-induced anomalies giving rise to pronounced features in the sample length for two out of these nine crystals for temperatures

T <

9 K. We tentatively assign the latter effects to B-induced magnetic clusters suspected to nucleate around crystal imperfections. These B-induced effects are absent for the crystals where the 6 K anomaly is most strongly pronounced. The large lattice effects observed at 6 K are consistent with proposed pairing instabilities of fermionic excitations breaking the lattice symmetry. The strong sample-to-sample variation in the size of the phase transition anomaly suggests that the conversion of the fermions to bosons at the instability is only partial and to some extent influenced by not yet identified sample-specific parameters. Full article

(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)

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17 pages, 6562 KiB

Open AccessArticle

A Standard Structure for Bile Acids and Derivatives

by Francisco Meijide, Santiago De Frutos, Victor H. Soto, Aida Jover, Julio A. Seijas, María Pilar Vázquez-Tato, Francisco Fraga and José Vázquez Tato

Crystals 2018, 8(2), 86; https://doi.org/10.3390/cryst8020086 - 6 Feb 2018

Cited by 6 | Viewed by 4968

Abstract

The crystal structures of two ester compounds (a monomer in its methyl ester form, with an amino isophthalic group, and a dimer in which the two steroid units are linked by a urea bridge recrystallized from ethyl acetate/methanol) derived from cholic acid are [...] Read more.

The crystal structures of two ester compounds (a monomer in its methyl ester form, with an amino isophthalic group, and a dimer in which the two steroid units are linked by a urea bridge recrystallized from ethyl acetate/methanol) derived from cholic acid are described. Average bond lengths and bond angles from the crystal structures of 26 monomers and four dimers (some of them in several solvents) of bile acids and esters (and derivatives) are used for proposing a standard steroid nucleus. The hydrogen bond network and conformation of the lateral chain are also discussed. This standard structure was used to compare with the structures of both progesterone and cholesterol. Full article

(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)

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12 pages, 8325 KiB

Open AccessArticle

Febuxostat-Minoxidil Salt Solvates: Crystal Structures, Characterization, Interconversion and Solubility Performance

by Li-Yang Li, Rong-Kai Du, You-Li Du, Chun-Jing Zhang, Su Guan, Chang-Zhi Dong and Lei Zhang

Crystals 2018, 8(2), 85; https://doi.org/10.3390/cryst8020085 - 5 Feb 2018

Cited by 11 | Viewed by 6146

Abstract

Three febuxostat-minoxidil salt solvates with acetone (ACE), tetrahydrofuran (THF) and isopropanol (IPA) are synthesized by solvent-assisted grinding and characterized by infrared (IR), nuclear magnetic resonance (¹H-NMR), single crystal and powder X-ray diffraction (PXRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). These [...] Read more.

Three febuxostat-minoxidil salt solvates with acetone (ACE), tetrahydrofuran (THF) and isopropanol (IPA) are synthesized by solvent-assisted grinding and characterized by infrared (IR), nuclear magnetic resonance (¹H-NMR), single crystal and powder X-ray diffraction (PXRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). These febuxostat-minoxidil salt solvates feature isostructural with the same stoichiometries (1:1:1 molecule ratio). The proton transfers from the carboxylic group of febuxostat (FEB) to imino N atom of minoxidil (MIN), which forms the motif with combined

R_{2}^{2}

(9)

R_{4}^{2}

(8)

R_{2}^{2}

(9) graph set in the three solvates. The solvents occupy the different positions related to the motif, which results in the apparent differences in PXRD patterns before/after desolvation although they are isostructures. The FEB-MIN·THF was more thermostable than FEB-MIN·ACE and FEB-MIN·IPA relative to solvent removal from DSC patterns, which is different from the results from the solvent-exchange experiments in chemical kinetics. All three salt solvates exhibit increased equilibrium solubility compared to FEB in aqueous medium. Full article

(This article belongs to the Special Issue Novel Pharmaceutical Cocrystals and Their Applications)

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22 pages, 23282 KiB

Open AccessArticle

The Carbonate Platform Model and Reservoirs’ Origins of the Callovian-Oxfordian Stage in the Amu Darya Basin, Turkmenistan

by Wenli Xu, Huaguo Wen, Rongcai Zheng, Fengjie Li, Fei Huo, Mingcai Hou and Gang Zhou

Crystals 2018, 8(2), 84; https://doi.org/10.3390/cryst8020084 - 4 Feb 2018

Cited by 7 | Viewed by 6880

Abstract

The Calloviane-Oxfordian carbonates in the northeastern Amu Darya Basin of southeastern Turkmenistan are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, brachiopods, echinoderms, foraminifera, corals, and sponge) and non-skeletal grains (intraclasts, ooids and peloids). Two facies zones, six standard [...] Read more.

The Calloviane-Oxfordian carbonates in the northeastern Amu Darya Basin of southeastern Turkmenistan are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, brachiopods, echinoderms, foraminifera, corals, and sponge) and non-skeletal grains (intraclasts, ooids and peloids). Two facies zones, six standard facies belts and some microfacies types were recognized, and sedimentary model “carbonate ramp-rimmed platform” was proposed and established that can be compared with the classical carbonate sedimentary models. In this model, favorable reservoirs not only developed in the intraplatform shoal of open platform, or reef and shoal on the platform margin, but also in the patch reefs, shoal and mound facies on the upper slope. The reservoir’s pore space is dominated by intergranular and intragranular pores and fissure-pore reservoirs exist with medium porosity and medium to low permeability. Sedimentary facies and diagenetic dissolution are the key controlling factors for the development of high-quality reservoirs. Full article

(This article belongs to the Special Issue Carbonates)

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16 pages, 9480 KiB

Open AccessEditor’s ChoiceReview

Multifunctional Aromatic Carboxylic Acids as Versatile Building Blocks for Hydrothermal Design of Coordination Polymers

by Jinzhong Gu, Min Wen, Xiaoxiao Liang, Zifa Shi, Marina V. Kirillova and Alexander M. Kirillov

Crystals 2018, 8(2), 83; https://doi.org/10.3390/cryst8020083 - 3 Feb 2018

Cited by 106 | Viewed by 8433

Abstract

Selected recent examples of coordination polymers (CPs) or metal-organic frameworks (MOFs) constructed from different multifunctional carboxylic acids with phenyl-pyridine or biphenyl cores have been discussed. Despite being still little explored in crystal engineering research, such types of semi-rigid, thermally stable, multifunctional and versatile [...] Read more.

Selected recent examples of coordination polymers (CPs) or metal-organic frameworks (MOFs) constructed from different multifunctional carboxylic acids with phenyl-pyridine or biphenyl cores have been discussed. Despite being still little explored in crystal engineering research, such types of semi-rigid, thermally stable, multifunctional and versatile carboxylic acid building blocks have become very promising toward the hydrothermal synthesis of metal-organic architectures possessing distinct structural features, topologies, and functional properties. Thus, the main aim of this mini-review has been to motivate further research toward the synthesis and application of coordination polymers assembled from polycarboxylic acids with phenyl-pyridine or biphenyl cores. The importance of different reaction parameters and hydrothermal conditions on the generation and structural types of CPs or MOFs has also been highlighted. The influence of the type of main di- or tricarboxylate ligand, nature of metal node, stoichiometry and molar ratio of reagents, temperature, and presence of auxiliary ligands or templates has been showcased. Selected examples of highly porous or luminescent CPs, compounds with unusual magnetic properties, and frameworks for selective sensing applications have been described. Full article

(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)

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16 pages, 4485 KiB

Open AccessArticle

Electrocrystallization of CaCO₃ Crystals Obtained through Phosphorylated Chitin

by Nicole Butto, Gustavo Cabrera-Barjas and Andrónico Neira-Carrillo

Crystals 2018, 8(2), 82; https://doi.org/10.3390/cryst8020082 - 3 Feb 2018

Cited by 14 | Viewed by 6212

Abstract

A phosphorylated chitin (Chi-P) derivative was synthesized and its chemical structure was verified with Fourier-transform infrared spectroscopy (FTIR), elemental analysis, and thermogravimetric techniques (TGA). The influence of Chi-P used as a solid template through in vitro electrocrystallization (EC) supported on an indium zinc [...] Read more.

A phosphorylated chitin (Chi-P) derivative was synthesized and its chemical structure was verified with Fourier-transform infrared spectroscopy (FTIR), elemental analysis, and thermogravimetric techniques (TGA). The influence of Chi-P used as a solid template through in vitro electrocrystallization (EC) supported on an indium zinc oxide (ITO) surface on the growth of calcium carbonate (CaCO₃) was studied. CaCO₃ crystals through EC essays were also compared with crystals obtained with the gas diffusion (GD) method. Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), chronopotentiometry, Raman, and powder X-ray diffractometry (XRD) characterized all resultant inorganic particles. Our findings revealed that the EC method selectively controlled the coexistence of truncate calcite and the metastable phase of vaterite. The crystals’ morphology reflects the electrostatic interaction of phosphate moieties from Chi-P onto CaCO₃ crystals through both EC and GD crystallization methods. We believe that the EC method represents a viable electrochemical approach for studying different inorganic minerals and could be useful as an in vitro classical crystallization method for the design of advanced inorganic materials with desirable shapes and properties. Full article

(This article belongs to the Special Issue Carbonates)

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11 pages, 2280 KiB

Open AccessArticle

High Pressure Induced Insulator-to-Semimetal Transition through Intersite Charge Transfer in NaMn₇O₁₂

by Davide Delmonte, Francesco Mezzadri, Fabio Orlandi, Gianluca Calestani, Yehezkel Amiel and Edmondo Gilioli

Crystals 2018, 8(2), 81; https://doi.org/10.3390/cryst8020081 - 3 Feb 2018

Cited by 4 | Viewed by 3724

Abstract

The pressure-dependent behaviour of NaMn₇O₁₂ (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18 [...] Read more.

The pressure-dependent behaviour of NaMn₇O₁₂ (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18 GPa, accompanied by a change in the compressibility of the system. On the other hand, the crystallographic determinations rule out a symmetry change to be at the origin of the transition, despite all the structural parameters pointing to a symmetrizing effect of pressure. Bond valence sum calculations indicate a charge transfer from the octahedrally coordinated manganese ions to the square planar ones, likely favouring the delocalization of the carriers. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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23 pages, 7084 KiB

Open AccessReview

Revealing Tendencies in the Electronic Structures of Polar Intermetallic Compounds

by Fabian C. Gladisch and Simon Steinberg

Crystals 2018, 8(2), 80; https://doi.org/10.3390/cryst8020080 - 2 Feb 2018

Cited by 30 | Viewed by 6240

Abstract

The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by [...] Read more.

The quest for solid-state materials with tailored chemical and physical features stimulates the search for general prescriptions to recognize and forecast their electronic structures providing valuable information about the experimentally determined bulk properties at the atomic scale. Although the concepts first introduced by Zintl and Hume–Rothery help to understand and forecast the bonding motifs in several intermetallic compounds, there is an emerging group of compounds dubbed as polar intermetallic phases whose electronic structures cannot be categorized by the aforementioned conceptions. These polar intermetallic compounds can be divided into two categories based on the building units in their crystal structures and the expected charge distributions between their components. On the one hand, there are polar intermetallic compounds composed of polycationic clusters surrounded by anionic ligands, while, on the other hand, the crystal structures of other polar intermetallic compounds comprise polyanionic units combined with monoatomic cations. In this review, we present the quantum chemical techniques to gain access to the electronic structures of polar intermetallic compounds, evaluate certain trends from a survey of the electronic structures of diverse polar intermetallic compounds, and show options based on quantum chemical approaches to predict the properties of such materials. Full article

(This article belongs to the Special Issue Functional Multi-Scale Crystals)

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22 pages, 6656 KiB

Open AccessArticle

Unravelling the High-Pressure Behaviour of Dye-Zeolite L Hybrid Materials

by Lara Gigli, Rossella Arletti, Ettore Fois, Gloria Tabacchi, Simona Quartieri, Vladimir Dmitriev and Giovanna Vezzalini

Crystals 2018, 8(2), 79; https://doi.org/10.3390/cryst8020079 - 2 Feb 2018

Cited by 16 | Viewed by 8125

Abstract

Self-assembly of chromophores nanoconfined in porous materials such as zeolite L has led to technologically relevant host-guest systems exploited in solar energy harvesting, photonics, nanodiagnostics and information technology. The response of these hybrid materials to compression, which would be crucial to enhance their [...] Read more.

Self-assembly of chromophores nanoconfined in porous materials such as zeolite L has led to technologically relevant host-guest systems exploited in solar energy harvesting, photonics, nanodiagnostics and information technology. The response of these hybrid materials to compression, which would be crucial to enhance their application range, has never been explored to date. By a joint high-pressure in situ synchrotron X-ray powder diffraction and ab initio molecular dynamics approach, herein we unravel the high-pressure behaviour of hybrid composites of zeolite L with fluorenone dye. High-pressure experiments were performed up to 6 GPa using non-penetrating pressure transmitting media to study the effect of dye loading on the structural properties of the materials under compression. Computational modelling provided molecular-level insight on the response to compression of the confined dye assemblies, evidencing a pressure-induced strengthening of the interaction between the fluorenone carbonyl group and zeolite L potassium cations. Our results reveal an impressive stability of the fluorenone-zeolite L composites at GPa pressures. The remarkable resilience of the supramolecular organization of dye molecules hyperconfined in zeolite L channels may open the way to the realization of optical devices able to maintain their functionality under extreme conditions. Full article

(This article belongs to the Special Issue Functional Multi-Scale Crystals)

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35 pages, 19400 KiB

Open AccessReview

Enhancing Light Extraction of Inorganic Scintillators Using Photonic Crystals

by Matteo Salomoni, Rosalinde Pots, Etiennette Auffray and Paul Lecoq

Crystals 2018, 8(2), 78; https://doi.org/10.3390/cryst8020078 - 1 Feb 2018

Cited by 50 | Viewed by 10874

Abstract

Inorganic scintillators are commonly used as sensors for ionizing radiation detectors in a variety of applications, ranging from particle and nuclear physics detectors, medical imaging, nuclear installations radiation control, homeland security, well oil logging and a number of industrial non-destructive investigations. For all [...] Read more.

Inorganic scintillators are commonly used as sensors for ionizing radiation detectors in a variety of applications, ranging from particle and nuclear physics detectors, medical imaging, nuclear installations radiation control, homeland security, well oil logging and a number of industrial non-destructive investigations. For all these applications, the scintillation light produced by the energy deposited in the scintillator allows the determination of the position, the energy and the time of the event. However, the performance of these detectors is often limited by the amount of light collected on the photodetector. A major limitation comes from the fact that inorganic scintillators are generally characterized by a high refractive index, as a consequence of the required high density to provide the necessary stopping power for ionizing radiation. The index mismatch between the crystal and the surrounding medium (air or optical grease) strongly limits the light extraction efficiency because of total internal reflection (TIR), increasing the travel path and the absorption probability through multiple bouncings of the photons in the crystal. Photonic crystals can overcome this problem and produce a controllable index matching between the crystal and the output medium through an interface made of a thin nano-structured layer of optically-transparent high index material. This review presents a summary of the works aiming at improving the light collection efficiency of scintillators using photonic crystals since this idea was introduced 10 years ago. Full article

(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)

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