Crystals

3189 KiB

Open AccessArticle

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R₁₁₇Co_52+δSn_112+γ (R = Y, La, Pr, Nd, Ho)

by Ping Chai, Mykola Abramchuk and Michael Shatruk

Crystals 2016, 6(12), 165; https://doi.org/10.3390/cryst6120165 - 20 Dec 2016

Cited by 14 | Viewed by 8209

Abstract

Ternary intermetallics R₁₁₇Co_52+δSn_112+γ (R = Y, La, Pr, Nd, and Ho) have been prepared by arc-melting followed by annealing at 800 °C. All the compounds belong to the Tb₁₁₇Fe₅₂Ge₁₁₂ structure type (space group [...] Read more.

Ternary intermetallics R₁₁₇Co_52+δSn_112+γ (R = Y, La, Pr, Nd, and Ho) have been prepared by arc-melting followed by annealing at 800 °C. All the compounds belong to the Tb₁₁₇Fe₅₂Ge₁₁₂ structure type (space group Fm

\bar{3}

m) characterized by a complex giant cubic unit cell with a ~ 30 Å. The single-crystal structure determination of Y- and La-containing compounds reveals a significant structural disorder. A comparison of these and earlier reported crystal structures of R₁₁₇Co_52+δSn_112+γ suggests that more extensive disorder occurs for structures that contain larger lanthanide atoms. This observation can be explained by the need to maintain optimal bonding interactions as the size of the unit cell increases. Y₁₁₇Co₅₆Sn₁₁₅ exhibits weak paramagnetism due to the Co sublattice and does not show magnetic ordering in the 1.8–300 K range. Ho₁₁₇Co₅₅Sn₁₀₈ shows ferromagnetic ordering at 10.6 K. Both Pr₁₁₇Co₅₄Sn₁₁₂ and Nd₁₁₇Co₅₄Sn₁₁₁ exhibit antiferromagnetic ordering at 17 K and 24.7 K, respectively, followed by a spin reorientation transition at lower temperature. Full article

(This article belongs to the Special Issue Correlated Electron Crystals)

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1740 KiB

Open AccessArticle

Raman and Terahertz Spectroscopic Investigation of Cocrystal Formation Involving Antibiotic Nitrofurantoin Drug and Coformer 4-aminobenzoic Acid

by Yong Du, Qiang Cai, Jiadan Xue and Qi Zhang

Crystals 2016, 6(12), 164; https://doi.org/10.3390/cryst6120164 - 16 Dec 2016

Cited by 14 | Viewed by 6948

Abstract

Cocrystallization could improve most physicochemical properties of specific active pharmaceutical ingredients, which has great potential in pharmaceutical development. In this study, the cocrystal of nitrofurantoin and 4-aminobenzoic acid was prepared with solid-state (solvent-free or green-chemistry) grinding approach, and the above cocrystal has been [...] Read more.

Cocrystallization could improve most physicochemical properties of specific active pharmaceutical ingredients, which has great potential in pharmaceutical development. In this study, the cocrystal of nitrofurantoin and 4-aminobenzoic acid was prepared with solid-state (solvent-free or green-chemistry) grinding approach, and the above cocrystal has been characterized by Raman and terahertz vibrational spectroscopic techniques. Spectral results show that the vibrational modes of the cocrystal within the whole spectral region are different from those of the corresponding parent materials. The dynamic process of such pharmaceutical cocrystal formation has also been monitored directly with Raman spectra. These results offer us unique means for characterizing the cocrystal conformation from the molecule-level, and provides us with rich information about the reaction dynamic of cocrystal formation within pharmaceutical fields. Full article

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

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4536 KiB

Open AccessReview

Molecular Structures and Second-Order Nonlinear Optical Properties of Ionic Organic Crystal Materials

by Xiu Liu, Zhou Yang, Dong Wang and Hui Cao

Crystals 2016, 6(12), 158; https://doi.org/10.3390/cryst6120158 - 14 Dec 2016

Cited by 102 | Viewed by 10858

Abstract

In recent years, there has been extensive research and continuous development on second-order nonlinear optical (NLO) crystal materials due to their potential applications in telecommunications, THz imaging and spectroscopy, optical information processing, and optical data storage. Recent progress in second-order NLO ionic organic [...] Read more.

In recent years, there has been extensive research and continuous development on second-order nonlinear optical (NLO) crystal materials due to their potential applications in telecommunications, THz imaging and spectroscopy, optical information processing, and optical data storage. Recent progress in second-order NLO ionic organic crystal materials is reviewed in this article. Research has shown that the second-order nonlinear optical properties of organic crystal materials are closely related to their molecular structures. The basic structures of ionic organic conjugated molecules with excellent nonlinear optical properties are summarized. The effects of molecular structure, for example, conjugated π electron systems, electronic properties of donor-acceptor groups, and different counter-anion effects on second order NLO properties and crystal packing are studied. Full article

(This article belongs to the Special Issue Nonlinear Optical Crystals)

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1629 KiB

Open AccessReview

Ferroelastic Domain Boundary-Based Multiferroicity

by Ekhard K. H. Salje and Xiangdong Ding

Crystals 2016, 6(12), 163; https://doi.org/10.3390/cryst6120163 - 9 Dec 2016

Cited by 10 | Viewed by 5582

Abstract

Domain boundary engineering endeavors to develop materials that contain localized functionalities inside domain walls, which do not exist in the bulk. Here we review multiferroic devices that are based on ferroelectricity inside ferroelastic domain boundaries. The discovery of polarity in CaTiO₃ and [...] Read more.

Domain boundary engineering endeavors to develop materials that contain localized functionalities inside domain walls, which do not exist in the bulk. Here we review multiferroic devices that are based on ferroelectricity inside ferroelastic domain boundaries. The discovery of polarity in CaTiO₃ and SrTiO₃ leads to new directions to produce complex domain patterns as templates for ferroic devices. Full article

(This article belongs to the Special Issue Multiferroics Crystals)

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3508 KiB

Open AccessArticle

Crystal Structure of the Substrate-Binding Domain from Listeria monocytogenes Bile-Resistance Determinant BilE

by Stephanie J. Ruiz, Gea K. Schuurman-Wolters and Bert Poolman

Crystals 2016, 6(12), 162; https://doi.org/10.3390/cryst6120162 - 9 Dec 2016

Cited by 6 | Viewed by 6139

Abstract

BilE has been reported as a bile resistance determinant that plays an important role in colonization of the gastrointestinal tract by Listeria monocytogenes, the causative agent of listeriosis. The mechanism(s) by which BilE mediates bile resistance are unknown. BilE shares significant sequence [...] Read more.

BilE has been reported as a bile resistance determinant that plays an important role in colonization of the gastrointestinal tract by Listeria monocytogenes, the causative agent of listeriosis. The mechanism(s) by which BilE mediates bile resistance are unknown. BilE shares significant sequence similarity with ATP-binding cassette (ABC) importers that contribute to virulence and stress responses by importing quaternary ammonium compounds that act as compatible solutes. Assays using related compounds have failed to demonstrate transport mediated by BilE. The putative substrate-binding domain (SBD) of BilE was expressed in isolation and the crystal structure solved at 1.5 Å. Although the overall fold is characteristic of SBDs, the binding site varies considerably relative to the well-characterized homologs ProX from Archaeoglobus fulgidus and OpuBC and OpuCC from Bacillus subtilis. This suggests that BilE may bind an as-yet unknown ligand. Elucidation of the natural substrate of BilE could reveal a novel bile resistance mechanism. Full article

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

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2943 KiB

Open AccessArticle

Structural and Spectral Properties of Deterministic Aperiodic Optical Structures

by Luca Dal Negro, Ren Wang and Felipe A. Pinheiro

Crystals 2016, 6(12), 161; https://doi.org/10.3390/cryst6120161 - 9 Dec 2016

Cited by 28 | Viewed by 8268

Abstract

In this comprehensive paper we have addressed structure-property relationships in a number of representative systems with periodic, random, quasi-periodic and deterministic aperiodic geometry using the interdisciplinary methods of spatial point pattern analysis and spectral graph theory as well as the rigorous Green’s matrix [...] Read more.

In this comprehensive paper we have addressed structure-property relationships in a number of representative systems with periodic, random, quasi-periodic and deterministic aperiodic geometry using the interdisciplinary methods of spatial point pattern analysis and spectral graph theory as well as the rigorous Green’s matrix method, which provides access to the electromagnetic scattering behavior and spectral fluctuations (distributions of complex eigenvalues as well as of their level spacing) of deterministic aperiodic optical media for the first time. Full article

(This article belongs to the Special Issue Structure and Properties of Quasicrystals 2016)

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1291 KiB

Open AccessArticle

Single Crystal Growth, Resistivity, and Electronic Structure of the Weyl Semimetals NbP and TaP

by Deepak Sapkota, Rupam Mukherjee and David Mandrus

Crystals 2016, 6(12), 160; https://doi.org/10.3390/cryst6120160 - 6 Dec 2016

Cited by 9 | Viewed by 6884

Abstract

We have successfully synthesized niobium monophosphide and tantalum monophosphide crystals by a chemical vapor transport technique. We report resistivity vs. temperature of both materials in the temperature range from 2 K to 300 K. We have also performed electronic structure calculations and present [...] Read more.

We have successfully synthesized niobium monophosphide and tantalum monophosphide crystals by a chemical vapor transport technique. We report resistivity vs. temperature of both materials in the temperature range from 2 K to 300 K. We have also performed electronic structure calculations and present the band structure and density of states of these two compounds. The calculations show that both compounds are semimetals, as their conduction and valence bands overlap near the Fermi energy. Full article

(This article belongs to the Special Issue Correlated Electron Crystals)

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3332 KiB

Open AccessFeature PaperArticle

Gas Source Techniques for Molecular Beam Epitaxy of Highly Mismatched Ge Alloys

by Chad A. Stephenson, Miriam Gillett-Kunnath, William A. O’Brien, Robert Kudrawiec and Mark A. Wistey

Crystals 2016, 6(12), 159; https://doi.org/10.3390/cryst6120159 - 2 Dec 2016

Cited by 6 | Viewed by 4786

Abstract

Ge and its alloys are attractive candidates for a laser compatible with silicon integrated circuits. Dilute germanium carbide (Ge_1−xC_x) offers a particularly interesting prospect. By using a precursor gas with a Ge₄C core, C can be preferentially [...] Read more.

Ge and its alloys are attractive candidates for a laser compatible with silicon integrated circuits. Dilute germanium carbide (Ge_1−xC_x) offers a particularly interesting prospect. By using a precursor gas with a Ge₄C core, C can be preferentially incorporated in substitutional sites, suppressing interstitial and C cluster defects. We present a method of reproducible and upscalable gas synthesis of tetrakis(germyl)methane, or (H₃Ge)₄C, followed by the design of a hybrid gas/solid-source molecular beam epitaxy system and subsequent growth of defect-free Ge_1−xC_x by molecular beam epitaxy (MBE). Secondary ion mass spectroscopy, transmission electron microscopy and contactless electroreflectance confirm the presence of carbon with very high crystal quality resulting in a decrease in the direct bandgap energy. This technique has broad applicability to growth of highly mismatched alloys by MBE. Full article

(This article belongs to the Special Issue Current and Future Directions in Crystal Growth by Molecular Beam Epitaxy (MBE))

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2539 KiB

Open AccessArticle

In Situ Studies on Phase Transitions of Tris(acetylacetonato)-Aluminum(III) Al(acac)₃

by Nicole Pienack, Laura Ruiz Arana, Wolfgang Bensch and Huayna Terraschke

Crystals 2016, 6(12), 157; https://doi.org/10.3390/cryst6120157 - 28 Nov 2016

Cited by 20 | Viewed by 8543

Abstract

In situ investigations on the nucleation and crystallization processes are essential for understanding of the formation of solids. Hence, the results of such experiments are prerequisites for the rational synthesis of solid materials. The in situ approach allows the detection of precursors, intermediates, [...] Read more.

In situ investigations on the nucleation and crystallization processes are essential for understanding of the formation of solids. Hence, the results of such experiments are prerequisites for the rational synthesis of solid materials. The in situ approach allows the detection of precursors, intermediates, and/or polymorphs, which are mainly missed in applying ex situ experiments. With a newly developed crystallization cell, simultaneous in situ experiments with X-ray diffraction (XRD) and luminescence analysis are possible, also monitoring several other reaction parameters. Here, the crystallization of the model system tris(acetylacetonato)-aluminum(III) Al(acac)₃ was investigated. In the time-resolved in situ XRD patterns, two polymorphs of Al(acac)₃, the α- and the γ-phase, were detected at room temperature and the influence of the pH value onto the product formation was studied. Moreover, changes in the emission of Al(acac)₃ and the light transmission of the solution facilitated monitoring the reaction by in situ luminescence. The first results demonstrate the potential of the cell to be advantageous for controlling and monitoring several reaction parameters during the crystallization process. Full article

(This article belongs to the Special Issue Mesocrystals and Hierarchical Structures)

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Crystals, Volume 6, Issue 12 (December 2016) – 9 articles

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