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Crystals, Volume 8, Issue 1 (January 2018)

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Editorial

Jump to: Research, Review

Open AccessEditorial Acknowledgement to Reviewers of Crystals in 2017
Crystals 2018, 8(1), 25; doi:10.3390/cryst8010025
Received: 9 January 2018 / Revised: 9 January 2018 / Accepted: 9 January 2018 / Published: 10 January 2018
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Abstract
Peer review is an essential part in the publication process, ensuring that Crystals maintains high quality standards for its published papers.[...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle Local Stress States and Microstructural Damage Response Associated with Deformation Twins in Hexagonal Close Packed Metals
Crystals 2018, 8(1), 1; doi:10.3390/cryst8010001
Received: 17 November 2017 / Revised: 13 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
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Abstract
The current work implements a correlative microscopy method utilizing electron back scatter diffraction, focused ion beam and digital image correlation to accurately determine spatially resolved stress profiles in the vicinity of grain/twin boundaries and tensile deformation twin tips in commercially pure titanium. Measured
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The current work implements a correlative microscopy method utilizing electron back scatter diffraction, focused ion beam and digital image correlation to accurately determine spatially resolved stress profiles in the vicinity of grain/twin boundaries and tensile deformation twin tips in commercially pure titanium. Measured local stress gradients were in good agreement with local misorientation values. The role of dislocation-boundary interactions on the buildup of local stress gradients is elucidated. Stress gradients across the twin-parent interface were compressive in nature with a maximum stress magnitude at the twin boundary. Stress profiles near certain grain boundaries initially display a local stress minimum, followed by a typically observed “one over square root of distance” variation, as was first postulated by Eshelby, Frank and Nabarro. The observed trends allude to local stress relaxation mechanisms very close to the grain boundaries. Stress states in front of twin tips showed tensile stress gradients, whereas the stress state inside the twin underwent a sign reversal. The findings highlight the important role of deformation twins and their corresponding interaction with grain boundaries on damage nucleation in metals. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Atomic Characterization of Byproduct Nanoparticles on Cesium Lead Halide Nanocrystals Using High-Resolution Scanning Transmission Electron Microscopy
Crystals 2018, 8(1), 2; doi:10.3390/cryst8010002
Received: 23 November 2017 / Revised: 20 December 2017 / Accepted: 20 December 2017 / Published: 22 December 2017
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Abstract
Recent microstructural studies on lead halide perovskite nanocrystals have consistently reported the coexistence of byproduct nanoparticles (NPs). However, the nature of these NPs and their formation mechanism are still a matter of debate. Herein, we have investigated the structure and compositions of the
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Recent microstructural studies on lead halide perovskite nanocrystals have consistently reported the coexistence of byproduct nanoparticles (NPs). However, the nature of these NPs and their formation mechanism are still a matter of debate. Herein, we have investigated the structure and compositions of the NPs located on colloidal cesium lead bromide nanocrystals (CsPbBr3 NCs), mainly through aberration-corrected transmission electron microscopy and spectroscopy. Our results show that these NPs can be assigned to PbBr2 and CsPb2Br5. The new CsPb2Br5 species are formed by reacting CsPbBr3 NCs with the remaining PbBr2 during the drying process. In addition, observation of the metallic Pb NPs are ascribed to the electron damage effect on CsPbBr3 NCs during transmission electron microscopy imaging. Full article
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Open AccessArticle Effects of Crystal Orientation on the Crack Propagation of Sapphire by Sequential Indentation Testing
Crystals 2018, 8(1), 3; doi:10.3390/cryst8010003
Received: 18 October 2017 / Revised: 15 December 2017 / Accepted: 20 December 2017 / Published: 25 December 2017
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Abstract
Single-crystal sapphire (α-Al2O3) is a hard and brittle material. Due to its highly crystalline nature, the fracture behavior of sapphire is strongly related to its crystal structure, and understanding the effects of crystal structure on the crack propagation of
[...] Read more.
Single-crystal sapphire (α-Al2O3) is a hard and brittle material. Due to its highly crystalline nature, the fracture behavior of sapphire is strongly related to its crystal structure, and understanding the effects of crystal structure on the crack propagation of sapphire is essential for the successful application of this important material (e.g., as wafers in the electronics industry). In the present work, crack propagation that is induced by sequential indentation was investigated on the A-plane and C-plane of sapphire using a Vickers indenter on a micrometer scale. It was found that increasing indentation depth obviously increases the rate of crack propagation on the A-plane, but this effect is not so obvious on the C-plane because of the different slip systems induced by indentation on the different crystal planes of sapphire. Moreover, some parallel linear traces along the A-plane, which fracture with increasing indentation depth, are observed from the residual indentation on the A-plane. The fracture toughness of both A-plane and C-plane sapphire is smaller after indentation testing than that obtained using conventional testing methods. The subsurface damage was detected by transmission electron microscopy (TEM). Full article
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Open AccessArticle Improved Stability and Photoluminescence Yield of Mn2+-Doped CH3NH3PbCl3 Perovskite Nanocrystals
Crystals 2018, 8(1), 4; doi:10.3390/cryst8010004
Received: 21 November 2017 / Revised: 18 December 2017 / Accepted: 20 December 2017 / Published: 23 December 2017
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Abstract
Organic–inorganic CH3NH3PbCl3 perovskite nanocrystals (PNCs) doped with Mn2+, CH3NH3PbxMn1−xCl3, have been successfully prepared using a reprecipitation method at room temperature. Structural and morphological characterizations reveal that the CH3NH3PbxMn1−xCl3 PNCs with cubic phase transforms from particles to cubes and increases in size from 16.2
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Organic–inorganic CH3NH3PbCl3 perovskite nanocrystals (PNCs) doped with Mn2+, CH3NH3PbxMn1−xCl3, have been successfully prepared using a reprecipitation method at room temperature. Structural and morphological characterizations reveal that the CH3NH3PbxMn1−xCl3 PNCs with cubic phase transforms from particles to cubes and increases in size from 16.2 ± 4.4 nm in average diameter to 25.3 ± 7.2 nm in cubic length after the addition of Mn2+ precursor. The CH3NH3PbxMn1−xCl3 PNCs exhibit a weak exciton emission at ~405 nm with a low absolute quantum yield (QY) of around 0.4%, but a strong Mn2+ dopant emission at ~610 nm with a high QY of around 15.2%, resulting from efficient energy transfer from the PNC host to the Mn2+ dopant via the 4T1→6A1 transition. In addition, the thermal and air stability of CH3NH3PbxMn1−xCl3 PNCs are improved due to the passivation with (3-aminopropyl) triethoxysilane (APTES), which is important for applications such as light emitting diodes (LEDs). Full article
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Open AccessArticle Liquid Crystal Ordering of Four-Base-Long DNA Oligomers with Both G–C and A–T Pairing
Crystals 2018, 8(1), 5; doi:10.3390/cryst8010005
Received: 20 November 2017 / Revised: 14 December 2017 / Accepted: 21 December 2017 / Published: 23 December 2017
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Abstract
We report the liquid crystal (LC) ordering in an aqueous solution of four-base-long DNA oligomers 5′-GCTA-3′. In such systems, the formation of the chiral nematic (N*) LC phase is the result of a continuous self-assembly process in which double helix stability is achieved
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We report the liquid crystal (LC) ordering in an aqueous solution of four-base-long DNA oligomers 5′-GCTA-3′. In such systems, the formation of the chiral nematic (N*) LC phase is the result of a continuous self-assembly process in which double helix stability is achieved only through linear chaining of multiple DNA strands. The thermal stability of the aggregates and their LC phase diagram have been experimentally investigated, quantitatively interpreted with theoretical models and compared with recent results on four-base sequences with only G–C or only A–T pairing motifs. N* phase is found at GCTA concentration, cDNA, between 240 and 480 mg/mL and at temperature T < 30 °C. The twist of the nematic director is found to be left-handed with pitch (p) in the optical range, increasing with cDNA and decreasing with T. Full article
(This article belongs to the Section Liquid Crystals)
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Open AccessArticle Solvent Dependent Disorder in M2(BzOip)2(H2O)·Solvate (M = Co or Zn)
Crystals 2018, 8(1), 6; doi:10.3390/cryst8010006
Received: 5 December 2017 / Revised: 19 December 2017 / Accepted: 19 December 2017 / Published: 24 December 2017
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Abstract
Coordination polymers derived from 5-benzyloxy isophthalic acid (H2BzOip) are rare, with only three reported that do not contain additional bridging ligands, of which two M2(BzOip)2(H2O) (M = Co and Zn) are isomorphous. It was hoped
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Coordination polymers derived from 5-benzyloxy isophthalic acid (H2BzOip) are rare, with only three reported that do not contain additional bridging ligands, of which two M2(BzOip)2(H2O) (M = Co and Zn) are isomorphous. It was hoped that by varying the solvent system in a reaction between H2BzOip and M(OAc)2 (M = Co and Zn), from water to a water/alcohol mixture, coordination polymers of different topology could be formed. Instead, two polymorphs of the existing M2(BzOip)2(H2O) (M = Co and Zn) were isolated from aqueous methanol and aqueous ethanol, in which a small number of guest solvent molecules are present in the crystals. These guest water molecules disrupt the hexaphenyl embrace motif, leading to varying degrees of disorder of the benzyl groups. Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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Open AccessArticle Synthesis and Luminescence Properties of New Metal-Organic Frameworks Based on Zinc(II) Ions and 2,5-Thiophendicarboxylate Ligands
Crystals 2018, 8(1), 7; doi:10.3390/cryst8010007
Received: 29 November 2017 / Revised: 21 December 2017 / Accepted: 22 December 2017 / Published: 24 December 2017
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Abstract
Six new metal-organic frameworks based on 2,5-thiophendicarboxylate (tdc2–) and zinc(II) ions were prepared in different reaction conditions, and their crystal structures were determined by XRD analysis. The compound [Zn(tdc)(dabco)(H2O)]∙DMF (1) is based on mononuclear Zn(II) ions connected
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Six new metal-organic frameworks based on 2,5-thiophendicarboxylate (tdc2–) and zinc(II) ions were prepared in different reaction conditions, and their crystal structures were determined by XRD analysis. The compound [Zn(tdc)(dabco)(H2O)]∙DMF (1) is based on mononuclear Zn(II) ions connected by tdc2– and dabco linkers into square-grid layered nets. The compound [Zn3(tdc)3(dabco)2] (2) is a rare example of monocoordinated dabco ligands in the metal-organic framework chemistry. Its crystal structure contains trinuclear linear carboxylate building units, connected into a distorted primitive cubic net. Similar trinuclear units were also found in [Zn5(tdc)4(Htdc)2(dabco)2]∙4DMF∙14H2O (3), although as a part of more complicated pentanuclear motives. The compound [Na2Zn(tdc)2(DMF)2] (4), quantitatively isolated by the addition of NaOH to the mixture of Zn(NO3)2 and H2tdc, is based on 1D chain motives, interconnected by tdc2– linkers into a three-dimensional framework. The compounds [Zn3(tdc)3(DMF)2]∙0.8DMF∙1.1H2O (5) and [Zn3(tdc)3(DMF)3]∙0.8DMF∙1.3H2O (6) were prepared in very similar reaction conditions, but with different times of heating, indirectly indicating higher thermodynamic stability of the three-dimensional metal-organic framework 6, compared to the two-dimensional metal-organic framework 5. The crystal structures of both 5 and 6 are based on the same trinuclear linear units as in 2. Luminescence properties of the compounds 46 were studied and compared with those for Na2tdc salt. In particular, the luminescence spectra of 4 practically coincide with those for the reference Na2tdc, while 5 and 6 exhibit coherent shifts of peaks to higher energies. Such hypsochromic shifts are likely associated with a different effective charge on the tdc2– anions in Na2tdc and sodium-containing 4, compared to zinc-based 5 and 6. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Nanoindentation-Induced Pile-Up in the Residual Impression of Crystalline Cu with Different Grain Size
Crystals 2018, 8(1), 9; doi:10.3390/cryst8010009
Received: 25 October 2017 / Revised: 9 December 2017 / Accepted: 19 December 2017 / Published: 26 December 2017
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Abstract
Nanoindentation morphologies of crystalline copper have been probed at the grain scale. Experimental tests have been conducted on nanocrystalline (NC), ultrafine-grained (UFG), and coarse-grained (CG) copper samples with a new Berkvoich indenter at the strain rate of 0.04/s without holding time at an
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Nanoindentation morphologies of crystalline copper have been probed at the grain scale. Experimental tests have been conducted on nanocrystalline (NC), ultrafine-grained (UFG), and coarse-grained (CG) copper samples with a new Berkvoich indenter at the strain rate of 0.04/s without holding time at an indentation depth of 2000 nm at room temperature. As the grain size increases, the height of the pile-up around the residual indentation increases and then exhibits a slightly decrease in the CG Cu. The maximum of the pile-up in the CG Cu obviously deviates from the center of the indenter sides. Our analysis has revealed that the dislocation motion and GB activities in the NC Cu, some cross- and multiple-slip dislocations inside the larger grain in the UFG Cu, and forest dislocations from the intragranular Frank-Read sources in the CG Cu would directly induce this distinct pile-up effect. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Structural Basis for the Influence of A1, 5A, and W51W57 Mutations on the Conductivity of the Geobacter sulfurreducens Pili
Crystals 2018, 8(1), 10; doi:10.3390/cryst8010010
Received: 15 November 2017 / Revised: 18 December 2017 / Accepted: 21 December 2017 / Published: 25 December 2017
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Abstract
The metallic-like conductivity of the Geobacter sulfurreducens pilus and higher conductivity of its mutants reflected that biological synthesis can be utilized to improve the properties of electrically conductive pili. However, the structural basis for diverse conductivities of nanowires remains uncertain. Here, the impacts
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The metallic-like conductivity of the Geobacter sulfurreducens pilus and higher conductivity of its mutants reflected that biological synthesis can be utilized to improve the properties of electrically conductive pili. However, the structural basis for diverse conductivities of nanowires remains uncertain. Here, the impacts of point mutations on the flexibility and stability of pilins were investigated based on molecular dynamics simulations. Structures of the G. sulfurreducens pilus and its mutants were constructed by Rosetta. Details of the structure (i.e., electrostatic properties, helical parameters, residue interaction network, distances between amino acids, and salt bridges) were analyzed by PDB2PQR, Rosetta, RING, PyMOL, and VMD, respectively. Changes in stability, flexibility, residue interaction, and electrostatic properties of subunits directly caused wild-type pilin and its mutants assemble different structures of G. sulfurreducens pili. By comparing the structures of pili with different conductivities, the mechanism by which the G. sulfurreducens pilus transfers electron along pili was attributed, at least in part, to the density of aromatic rings, the distances between neighboring aromatic rings, and the local electrostatic environment around aromatic contacts. These results provide new insight into the potential for the biological synthesis of highly electrically conductive, nontoxic nanowires. Full article
(This article belongs to the Special Issue Crystal Structures of Amino Acids and Peptides)
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Open AccessArticle Synthesis and Characterization of Barium Hexafluoridoosmates
Crystals 2018, 8(1), 11; doi:10.3390/cryst8010011
Received: 27 November 2017 / Revised: 22 December 2017 / Accepted: 24 December 2017 / Published: 29 December 2017
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Abstract
Two barium hexafluoridoosmates, Ba(OsF6)2 and BaOsF6, were synthesized and were characterized for the first time using X-ray powder and single crystal diffraction, IR spectroscopy, as well as NMR spectroscopy in anhydrous hydrogen fluoride. Ba(OsF6)2 crystallizes
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Two barium hexafluoridoosmates, Ba(OsF6)2 and BaOsF6, were synthesized and were characterized for the first time using X-ray powder and single crystal diffraction, IR spectroscopy, as well as NMR spectroscopy in anhydrous hydrogen fluoride. Ba(OsF6)2 crystallizes in the space group type P21/c with the cell parameters a = 6.4599(4), b = 10.7931(8), c = 14.7476(10) Å, β = 115.195(5)°, V = 930.42(12) Å3, Z = 4 at 293 K. BaOsF6 crystallizes in the space group type R 3 ¯ with the cell parameters a = 7.3286(10), c = 7.2658(15) Å, V = 337.95(12) Å3, Z = 3 at 100 K. Additionally, we have obtained the compounds Ba(OsF6)2∙3BrF3, Ba(OsF6)2∙HF, Ba(OsF6)2∙6H2O from the respective solvents, and Ba(OsF6)2. Full article
(This article belongs to the Special Issue Structure and Properties of Fluoride-based Materials)
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Open AccessArticle Identification and Crystallographic Analysis of a New Carbohydrate Acetylesterase (SmAcE1) from Sinorhizobium meliloti
Crystals 2018, 8(1), 12; doi:10.3390/cryst8010012
Received: 23 October 2017 / Revised: 20 December 2017 / Accepted: 24 December 2017 / Published: 1 January 2018
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Abstract
Carbohydrate-active enzymes (CAZymes) regulate the synthesis, degradation, and modification of the poly—and oligosaccharides in all three kingdoms of life. A novel carbohydrate acetylesterase from Sinorhizobium meliloti, designated SmAcE1, was identified, characterized, and crystallized. This SmAcE1 is classified into the carbohydrate esterase family
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Carbohydrate-active enzymes (CAZymes) regulate the synthesis, degradation, and modification of the poly—and oligosaccharides in all three kingdoms of life. A novel carbohydrate acetylesterase from Sinorhizobium meliloti, designated SmAcE1, was identified, characterized, and crystallized. This SmAcE1 is classified into the carbohydrate esterase family 3 (CE3) based on the sequence alignments with other currently known carbohydrate esterase (CE) family enzymes. The SmAcE1 was crystallized as a hexamer in a space group P212121 with the unit cell parameters: a = 99.12 Å, b = 148.88 Å, c = 149.84 Å, and α = β = γ = 90.00°. The diffraction data set was collected up to a 2.05 Å resolution. Hydrolysis activity of SmAcE1 towards glucose pentaacetate and cellulose acetate was further confirmed using acetic acid release assay. Further crystallographic and functional analyses studies on SmAcE1 would be followed to fully understand the reaction mechanisms of CEs. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle In Situ Random Microseeding and Streak Seeding Used for Growth of Crystals of Cold-Adapted β-d-Galactosidases: Crystal Structure of βDG from Arthrobacter sp. 32cB
Crystals 2018, 8(1), 13; doi:10.3390/cryst8010013
Received: 29 November 2017 / Revised: 28 December 2017 / Accepted: 29 December 2017 / Published: 1 January 2018
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Abstract
There is an increasing demand for cold-adapted enzymes in a wide range of industrial branches. Nevertheless, structural information about them is still scarce. The knowledge of crystal structures is important to understand their mode of action and to design genetically engineered enzymes with
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There is an increasing demand for cold-adapted enzymes in a wide range of industrial branches. Nevertheless, structural information about them is still scarce. The knowledge of crystal structures is important to understand their mode of action and to design genetically engineered enzymes with enhanced activity. The most difficult task and the limiting step in structural studies of cold-adapted enzymes is their crystallization, which should provide well-diffracting monocrystals. Herein, we present a combination of well-established crystallization methods with new protocols based on crystal seeding that allowed us to obtain well-diffracting crystals of two cold-adapted β-d-galactosidases (βDGs) from Paracoccus sp. 32d (ParβDG) and from Arthrobacter sp. 32cB (ArthβDG). Structural studies of both βDGs are important for designing efficient and inexpensive enzymatic tools for lactose removal and synthesis of galacto-oligosaccharides (GOS) and hetero-oligosaccharides (HOS), food additives proved to have a beneficial effect on the human immune system and intestinal flora. We also present the first crystal structure of ArthβDG (PDB ID: 6ETZ) determined at 1.9 Å resolution, and compare it to the ParβDG structure (PDB ID: 5EUV). In contrast to tetrameric lacZ βDG and hexameric βDG from Arthrobacter C2-2, both of these βDGs are dimers, unusual for the GH2 family. Additionally, we discuss the various crystallization seeding protocols, which allowed us to obtain ParβDG and ArthβDG monocrystals suitable for diffraction experiments. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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Open AccessArticle A One-Dimensional Coordination Polymer Containing Cyclic [Ag4] Clusters Supported by a Hybrid Pyridine and Thioether Functionalized 1,2,3-Triazole
Crystals 2018, 8(1), 16; doi:10.3390/cryst8010016
Received: 7 December 2017 / Revised: 28 December 2017 / Accepted: 28 December 2017 / Published: 2 January 2018
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Abstract
A pyridine and thioether co-supported triazole ligand L (L = 2-((4-(3-(cyclopentylthio)propyl)-1H-1,2,3-triazol-1-yl)methyl)pyridine) has been synthesized using the CuAAC click reaction. This ligand supports the formation of a thermally stable, one-dimensional coordination polymer [L2Ag4]n·4n(BF4
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A pyridine and thioether co-supported triazole ligand L (L = 2-((4-(3-(cyclopentylthio)propyl)-1H-1,2,3-triazol-1-yl)methyl)pyridine) has been synthesized using the CuAAC click reaction. This ligand supports the formation of a thermally stable, one-dimensional coordination polymer [L2Ag4]n·4n(BF4) (1) possessing a cationic polymeric structure with [Ag4] metallomacrocycles, in which the ligand L displays chelate/bridging coordination modes using all four potential donors of nitrogen (N) and thioether (S). The dominant direction of the prism crystals of 1 aligns with the propagation of the chain in the lattice. Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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Open AccessArticle Removal of SO42− from Li2CO3 by Recrystallization in Na2CO3 Solution
Crystals 2018, 8(1), 19; doi:10.3390/cryst8010019
Received: 4 December 2017 / Revised: 29 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
Li2CO3 with high purity is an important raw material for the fabrication of lithium rechargeable batteries. This paper reports a facile recrystallization way to produce Li2CO3 with high purity from commercial Li2CO3 containing 0.8
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Li2CO3 with high purity is an important raw material for the fabrication of lithium rechargeable batteries. This paper reports a facile recrystallization way to produce Li2CO3 with high purity from commercial Li2CO3 containing 0.8 wt % of SO42− by the treatment of the commercial Li2CO3 in Na2CO3 solution. The increase of temperature from 30 °C to 90 °C favored the recrystallization of Li2CO3 in Na2CO3 solution and promoted the removal of SO42− adsorbed or doped on/in the commercial Li2CO3. The content of SO42− in Li2CO3 decreased to 0.08 wt % after the treatment of the commercial Li2CO3 in 1.0 mol·L−1 Na2CO3 solution at 90 °C for 10.0 h. Full article
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Open AccessArticle A Robust Framework Based on Polymeric Octamolybdate Anions and Copper(II) Complexes of Tetradentate N-donor Ligands
Crystals 2018, 8(1), 20; doi:10.3390/cryst8010020
Received: 14 December 2017 / Revised: 3 January 2018 / Accepted: 4 January 2018 / Published: 6 January 2018
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Abstract
A new organic-inorganic compound based on octamolybdate building blocks and copper(II) complexes of tetradentate N-donor ligands has been hydrothermally synthesized, namely [Cu(cyclam)]2[Mo8O26]·1.5H2O (1), (cyclam: 1,4,8,11–tetraazacyclotetradecane). Compound 1 has been chemically (elemental and thermal
[...] Read more.
A new organic-inorganic compound based on octamolybdate building blocks and copper(II) complexes of tetradentate N-donor ligands has been hydrothermally synthesized, namely [Cu(cyclam)]2[Mo8O26]·1.5H2O (1), (cyclam: 1,4,8,11–tetraazacyclotetradecane). Compound 1 has been chemically (elemental and thermal analyses), spectroscopically (infrared spectroscopy), and structurally (single crystal and powder X-ray diffraction) characterized. The crystal packing of 1 shows a covalent framework structure formed by [Mo8O26]n4n− chains running along the 100 direction which are linked to each other through the coordination spheres of {Cu(cyclam)}2+ complexes leading to a three-dimensional open network. This structural assembly generates voids that can be described as a succession of cavities communicated through narrow bottlenecks with approximate cross section of 4 × 7 Å2 where the hydration water molecules are hosted. The robust open structure of 1 remains virtually unaltered upon thermal evacuation of guest solvent molecules at 130 °C, resulting in the anhydrous phase [Cu(cyclam)]2[Mo8O26] (1a) with potentially accessible micropores as demonstrated by single-crystal X-ray diffraction measurements. Electron paramagnetic resonance spectroscopy analysis of 1 has also been assessed. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Analysis of Bending Waves in Phononic Crystal Beams with Defects
Crystals 2018, 8(1), 21; doi:10.3390/cryst8010021
Received: 15 October 2017 / Revised: 21 December 2017 / Accepted: 3 January 2018 / Published: 6 January 2018
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Abstract
Existing investigations on imperfect phononic crystal beams mainly concern periodic multi-span beams carrying either one or two channel waves with random or deterministic disorder in span-length. This paper studies the two channel bending waves in phononic crystal beams consisting of many phases of
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Existing investigations on imperfect phononic crystal beams mainly concern periodic multi-span beams carrying either one or two channel waves with random or deterministic disorder in span-length. This paper studies the two channel bending waves in phononic crystal beams consisting of many phases of materials with defects introduced as one structural segment having different cross-sectional dimensions or material parameters. The method of reverberation-ray matrix (MRRM) based on the Timoshenko beam theory, which can conduct high-frequency analysis, is extended for the theoretical analysis of dispersion and transmission of bending waves. The supercell technique and the Floquet–Bloch theorem are adopted for modeling the dispersion characteristics, and the whole finite structural model is used to calculate the transmission spectra. Experimental measurements and numerical calculations are provided to validate the displacement transmission obtained by the proposed MRRM, with the effect of damping on transmission spectra being concerned. The high-frequency calculation applicability of the proposed MRRM is also confirmed by comparing the present results with the corresponding ones either using the transfer matrix method (TMM) or MRRM based on Euler—Bernoulli beam theory. The influences of defect size, defect form, and unit-cell number on the transmission spectra and the band structures are discussed. The drawn conclusions may be useful for designing or evaluating the defected phononic crystal beams in bending wave control. In addition, our conclusions are especially potential for identifying the defect location through bending wave signals. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle Controllable Molecular Packing Motif and Overlap Type in Organic Nanomaterials for Advanced Optical Properties
Crystals 2018, 8(1), 22; doi:10.3390/cryst8010022
Received: 3 November 2017 / Revised: 1 January 2018 / Accepted: 4 January 2018 / Published: 11 January 2018
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Abstract
The optical properties of organic materials are very sensitive to subtle structural modification, and a proper understanding of the structure-property relationship is essential to improve the performance of organic electronic devices. The phase transitions of the η-CuPc to the α-CuPc, then to the
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The optical properties of organic materials are very sensitive to subtle structural modification, and a proper understanding of the structure-property relationship is essential to improve the performance of organic electronic devices. The phase transitions of the η-CuPc to the α-CuPc, then to the β-CuPc were investigated using In situ X-ray diffraction and the differential scanning calorimetry (DSC). The five stages in the phase-transition process from low to high-temperature were observed, which consisted of (1) the η-CuPc; (2) a mixture of the η- and α-CuPc; (3) a mixture of the η-, α- and β-CuPc; (4) a mixture of the α- and β-CuPc; and (5) the β-CuPc. The vibrational and optical properties at different phase-transition stages were correlated to molecular packing motif and molecule overlap type through systematic analyses of the Fourier–transform infrared, Raman and UV-VIS spectra. Moreover, the mechanism for the morphology evolution was also discussed in detail. Full article
(This article belongs to the Special Issue Advance in Crystalline Thin Wires)
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Open AccessArticle Prussian Blue Analogue Mesoframes for Enhanced Aqueous Sodium-ion Storage
Crystals 2018, 8(1), 23; doi:10.3390/cryst8010023
Received: 24 November 2017 / Revised: 22 December 2017 / Accepted: 3 January 2018 / Published: 7 January 2018
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Abstract
Mesostructure engineering is a potential avenue towards the property control of coordination polymers in addition to the traditional structure design on an atomic/molecular scale. Mesoframes, as a class of mesostructures, have short diffusion pathways for guest species and thus can be an ideal
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Mesostructure engineering is a potential avenue towards the property control of coordination polymers in addition to the traditional structure design on an atomic/molecular scale. Mesoframes, as a class of mesostructures, have short diffusion pathways for guest species and thus can be an ideal platform for fast storage of guest ions. We report a synthesis of Prussian Blue analogue mesoframes by top-down etching of cubic crystals. Scanning and transmission electron microscopy revealed that the surfaces of the cubic crystals were selectively removed by HCl, leaving the corners, edges, and the cores connected together. The mesoframes were used as a host for the reversible insertion of sodium ions with the help of electrochemistry. The electrochemical intercalation/de-intercalation of Na+ ions in the mesoframes was highly reversible even at a high rate (166.7 C), suggesting that the mesoframes could be a promising cathode material for aqueous sodium ion batteries with excellent rate performance and cycling stability. Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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Open AccessArticle Observations on Nanoscale Te Precipitates in CdZnTe Crystals Grown by the Traveling Heater Method Using High Resolution Transmission Electron Microscopy
Crystals 2018, 8(1), 26; doi:10.3390/cryst8010026
Received: 20 December 2017 / Revised: 3 January 2018 / Accepted: 8 January 2018 / Published: 10 January 2018
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Abstract
Te precipitates in CdZnTe (CZT) crystals grown by the traveling heater method (THM) are investigated using high-resolution transmission electron microscopy (HRTEM). The results show that in THM-grown CZT crystals, Te precipitates are less than 10 nm in size—much smaller than those in Bridgman-grown
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Te precipitates in CdZnTe (CZT) crystals grown by the traveling heater method (THM) are investigated using high-resolution transmission electron microscopy (HRTEM). The results show that in THM-grown CZT crystals, Te precipitates are less than 10 nm in size—much smaller than those in Bridgman-grown CZT. They have hexagonal structure and form a coherent interface with zinc blend structure CZT matrix in the orientation relationship [ 1 ¯ 12 ] M / / [ 0001 ] P and ( 1 1 ¯ 1 ) M / / ( 1 ¯ 100 ) P . A ledge growth interface with the preferred orientation along the [ 1 1 ¯ 1 ] M and [ 110 ] M was found near Te precipitates. The growth and nucleation mechanism of Te precipitates are also discussed. Full article
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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Open AccessArticle Evaluation of Light Extraction Efficiency of GaN-Based Nanorod Light-Emitting Diodes by Averaging over Source Positions and Polarizations
Crystals 2018, 8(1), 27; doi:10.3390/cryst8010027
Received: 15 December 2017 / Revised: 7 January 2018 / Accepted: 8 January 2018 / Published: 10 January 2018
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Abstract
Light extraction efficiency (LEE) of GaN-based nanorod blue light-emitting diode (LED) structures is investigated using finite-difference time-domain (FDTD) simulations. When the LEE is calculated for different source positions inside the nanorod, the LEE is found to depend strongly on the source positions and
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Light extraction efficiency (LEE) of GaN-based nanorod blue light-emitting diode (LED) structures is investigated using finite-difference time-domain (FDTD) simulations. When the LEE is calculated for different source positions inside the nanorod, the LEE is found to depend strongly on the source positions and the polarization directions for each source position, implying that the LEE of nanorod LED structures should be evaluated by averaging over source positions and polarization directions for determining the LEE accurately. The averaged LEE of nanorod LED structures is simulated as the radius, the p-GaN thickness, and the n-GaN thickness is varied, and the optimum structural parameters can be obtained. In addition, the far-field pattern is simulated when considering the averaging effects, and the circularly symmetric and uniform emission distribution is obtained. Full article
(This article belongs to the Special Issue Advances in GaN Crystals and Their Applications)
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Open AccessArticle Interface Effects on Screw Dislocations in Heterostructures
Crystals 2018, 8(1), 28; doi:10.3390/cryst8010028
Received: 14 November 2017 / Revised: 6 January 2018 / Accepted: 8 January 2018 / Published: 10 January 2018
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Abstract
The governing equation of screw dislocations in heterostructures is constructed using image method. The interface type (1γ1) and distance between dislocation and interface h are considered in the new equation. The Peierls–Nabarro equations for screw dislocations
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The governing equation of screw dislocations in heterostructures is constructed using image method. The interface type ( 1 γ 1 ) and distance between dislocation and interface h are considered in the new equation. The Peierls–Nabarro equations for screw dislocations in bulk and semi-infinite materials can be recovered when γ = 0 and γ = 1 . The soft ( γ < 0 ) and hard ( γ > 0 ) interfaces can enhance and reduce the Peierls stress of screw dislocations near the interface, respectively. The interface effects on dislocations decrease with the increasing of distance h. The Al/TiC heterostructure is investigated as a model interface to study the unstable stacking fault energy and dislocation properties of the interface. The mismatch of lattice constants and shear modulus at the interface results in changes of the unstable stacking fault energy. Then, the changes of the unstable stacking fault energy also have an important effect on dislocation properties, comparing with γ and h. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessArticle Incorporating the Thiazolo[5,4-d]thiazole Unit into a Coordination Polymer with Interdigitated Structure
Crystals 2018, 8(1), 30; doi:10.3390/cryst8010030
Received: 21 December 2017 / Revised: 5 January 2018 / Accepted: 6 January 2018 / Published: 12 January 2018
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Abstract
The linker 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole (Dptztz), whose synthesis and structure is described here, was utilized together with benzene-1,3-dicarboxylate (isophthalate, 1,3-BDC2−) for the preparation of the two-dimensional coordination network [Zn(1,3-BDC)Dptztz]·DMF (DMF = dimethylformamide) via a solvothermal reaction. Compound [Zn(1,3-BDC)Dptztz]·DMF belongs to the class of
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The linker 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole (Dptztz), whose synthesis and structure is described here, was utilized together with benzene-1,3-dicarboxylate (isophthalate, 1,3-BDC2−) for the preparation of the two-dimensional coordination network [Zn(1,3-BDC)Dptztz]·DMF (DMF = dimethylformamide) via a solvothermal reaction. Compound [Zn(1,3-BDC)Dptztz]·DMF belongs to the class of coordination polymers with interdigitated structure (CIDs). The incorporated DMF solvent molecules can be removed through solvent exchange and evacuation such that the supramolecular 3D packing of the 2D networks retains porosity for CO2 adsorption in activated [Zn(1,3-BDC)Dptztz]. The first sorption study of a tztz-functionalized porous metal-organic framework material yields a BET surface of 417 m2/g calculated from the CO2 adsorption data. The heat of adsorption for CO2 exhibits a relative maximum with 27.7 kJ/mol at an adsorbed CO2 amount of about 4 cm3/g STP, which is interpreted as a gate-opening effect. Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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Open AccessArticle Influence of Abrasive Shape on the Abrasion and Phase Transformation of Monocrystalline Silicon
Crystals 2018, 8(1), 32; doi:10.3390/cryst8010032
Received: 22 December 2017 / Revised: 4 January 2018 / Accepted: 5 January 2018 / Published: 12 January 2018
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Abstract
The effect of abrasive shape on the three-body abrasion behaviors of monocrystalline silicon was investigated via molecular dynamics. The axial ratio of abrasive particle varied from 1.00 to 0.40 to mimic abrasive shape. It has been observed that the particle’s movement became sliding
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The effect of abrasive shape on the three-body abrasion behaviors of monocrystalline silicon was investigated via molecular dynamics. The axial ratio of abrasive particle varied from 1.00 to 0.40 to mimic abrasive shape. It has been observed that the particle’s movement became sliding instead of rolling when the axial ratio was smaller than a critical value 0.46. In the abrasion process, the friction force and normal force showed an approximately sinusoid-like fluctuation for the rolling ellipsoidal particles, while the front cutting of particle caused that friction force increased and became larger than normal force for sliding particles. The phase transformation process was tracked under different particle’ movement patterns. The Si-II and Bct5 phase producing in loading process can partially transform to Si-III/Si-XII phase, and backtrack to original crystal silicon under pressure release, which also occurred in the abrasion process. The secondary phase transformation showed difference for particles’ rolling and sliding movements after three-body abrasion. The rolling of particle induced the periodical and inhomogeneous deformation of substrates, while the sliding benefited producing high-quality surface in chemical mechanical polishing (CMP) process. This study aimed to construct a more precise model to understand the wear mechanism benefits evaluating the micro-electro-mechanical systems (MEMS) wear and CMP process of crystal materials. Full article
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Open AccessArticle Sigma-Holes in Battery Materials Using Iso-Electrostatic Potential Surfaces
Crystals 2018, 8(1), 33; doi:10.3390/cryst8010033
Received: 18 December 2017 / Revised: 9 January 2018 / Accepted: 10 January 2018 / Published: 12 January 2018
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Abstract
The presence of highly electronegative atoms in Li-ion batteries anticipates the formation of σ-hole regions that may strongly affect the ionic conductivity. The σ-hole consists of a region of positive electrostatic potential extending in the direction of the covalent bond between atoms of
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The presence of highly electronegative atoms in Li-ion batteries anticipates the formation of σ-hole regions that may strongly affect the ionic conductivity. The σ-hole consists of a region of positive electrostatic potential extending in the direction of the covalent bond between atoms of groups IV–VII due to anisotropic charge distribution. Graphite electrodes in Li-ion batteries that become halogenated due to the electrolyte, as well as some solid electrolyte materials, can exhibit these σ-holes. Since Li-ions should be able to drift in any part of the battery, the fact that they can be attracted and eventually absorbed by regions of strong negative potentials produced by high-electronegativity counterions becomes detrimental to ionic conductivity. Therefore, the presence of positive well-defined regions, repulsive to the Li-ions, might act as lubricant for Li-ions drifting through electrolytes, thus improving the Li-ion conductivity. In addition, the σ-holes might also have a strong effect on the formation of the passivating layer, known as the solid electrolyte interphase (SEI) at electrode surfaces, which is of paramount importance for the performance of rechargeable batteries. Here we investigate the existence of σ-holes on surfaces of graphite anodes and of a few solid electrolytes by examining the electrostatic potentials calculated using density functional theory. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle Modeling and Analysis of Novel Horizontal Ribbon Growth of Silicon Crystal
Crystals 2018, 8(1), 36; doi:10.3390/cryst8010036 (registering DOI)
Received: 7 December 2017 / Revised: 30 December 2017 / Accepted: 9 January 2018 / Published: 16 January 2018
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Abstract
We present a novel horizontal ribbon growth (HRG) process and a theoretical analysis of this method. Assuming that the existence of the meniscus is defined by diffuse growth, we determine analytically the thickness and height of the meniscus and an explicit expression for
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We present a novel horizontal ribbon growth (HRG) process and a theoretical analysis of this method. Assuming that the existence of the meniscus is defined by diffuse growth, we determine analytically the thickness and height of the meniscus and an explicit expression for the performance of meniscus under different conditions. We then calculate the thermal profile in melt part, as well as the conditions under which the undercooling is sufficient around the solidification point. We find that diffuse growth is more sensitive to small initial thickness, and find the minimum length of the melt part to obtain undercooling. Finally, we calculate the change rule of solidification position by a variational approach, as well as the stability of the process under different conditions. We also give an expression to the instability of past HRG methods. Full article
(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)
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Open AccessCommunication Synthesis and Crystal Structure of a Zn(II)-Based MOF Bearing Neutral N-Donor Linker and SiF62− Anion
Crystals 2018, 8(1), 37; doi:10.3390/cryst8010037 (registering DOI)
Received: 20 November 2017 / Revised: 10 January 2018 / Accepted: 10 January 2018 / Published: 16 January 2018
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Abstract
A novel three-dimensional two-fold interpenetrated bi-porous metal-organic framework IPM-325 (IPM: IISER Pune Materials) having pcu topology was synthesized at room temperature. Single crystal X-ray diffraction (SC-XRD) study revealed that the compound crystallizes in monoclinic lattice with molecular formula {[Zn(L)2 (SiF6)]
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A novel three-dimensional two-fold interpenetrated bi-porous metal-organic framework IPM-325 (IPM: IISER Pune Materials) having pcu topology was synthesized at room temperature. Single crystal X-ray diffraction (SC-XRD) study revealed that the compound crystallizes in monoclinic lattice with molecular formula {[Zn(L)2 (SiF6)] (CH2Cl2) xG}n where G = Guests). All metal centers were found to have octahedral geometry. From single crystal analysis it can be inferred that SiF62− anion play a vital role in extending the dimensionality of the framework by bridging between two metal centers. Interestingly, IPM-325 exhibited two-step structural transformation maintaining the crystallinity of the framework as characterized by powder X-ray diffraction (PXRD). Full article
(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)
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Open AccessArticle Effects of Disorder on the Pressure-Induced Mott Transition in κ-(BEDT-TTF)2Cu[N(CN)2]Cl
Crystals 2018, 8(1), 38; doi:10.3390/cryst8010038 (registering DOI)
Received: 14 December 2017 / Revised: 9 January 2018 / Accepted: 11 January 2018 / Published: 16 January 2018
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Abstract
We present a study of the influence of disorder on the Mott metal-insulator transition for the organic charge-transfer salt κ-(BEDT-TTF)2Cu[N(CN)2]Cl. To this end, disorder was introduced into the system in a controlled way by exposing the single crystals
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We present a study of the influence of disorder on the Mott metal-insulator transition for the organic charge-transfer salt κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. To this end, disorder was introduced into the system in a controlled way by exposing the single crystals to X-ray irradiation. The crystals were then fine-tuned across the Mott transition by the application of continuously controllable He-gas pressure at low temperatures. Measurements of the thermal expansion and resistance show that the first-order character of the Mott transition prevails for low irradiation doses achieved by irradiation times up to 100 h. For these crystals with a moderate degree of disorder, we find a first-order transition line which ends in a second-order critical endpoint, akin to the pristine crystals. Compared to the latter, however, we observe a significant reduction of both, the critical pressure p c and the critical temperature T c . This result is consistent with the theoretically-predicted formation of a soft Coulomb gap in the presence of strong correlations and small disorder. Furthermore, we demonstrate, similar to the observation for the pristine sample, that the Mott transition after 50 h of irradiation is accompanied by sizable lattice effects, the critical behavior of which can be well described by mean-field theory. Our results demonstrate that the character of the Mott transition remains essentially unchanged at a low disorder level. However, after an irradiation time of 150 h, no clear signatures of a discontinuous metal-insulator transition could be revealed anymore. These results suggest that, above a certain disorder level, the metal-insulator transition becomes a smeared first-order transition with some residual hysteresis. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle CO2 Capture and Crystallization of Ammonia Bicarbonate in a Lab-Scale Scrubber
Crystals 2018, 8(1), 39; doi:10.3390/cryst8010039 (registering DOI)
Received: 21 November 2017 / Revised: 9 January 2018 / Accepted: 12 January 2018 / Published: 16 January 2018
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Abstract
A lab-scale bubble-column scrubber is used to capture CO2 gas and produce ammonia bicarbonate (ABC) using aqueous ammonia as an absorbent under a constant pH and temperature. The CO2 concentration is adjusted by mixing N2 and CO2 in the
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A lab-scale bubble-column scrubber is used to capture CO2 gas and produce ammonia bicarbonate (ABC) using aqueous ammonia as an absorbent under a constant pH and temperature. The CO2 concentration is adjusted by mixing N2 and CO2 in the range of 15–60 vol % at 55 °C. The process variables are the pH of the solution, temperature, gas-flow rate and the concentration of gas. The effects of the process variables on the removal efficiency (E), absorption rate (RA) and overall mass-transfer coefficient (KGa) were explored. A multiple-tube mass balance model was used to determine RA and KGa, in which RA and KGa were in the range of 2.14 × 10−4–1.09 × 10−3 mol/(s·L) and 0.0136–0.5669 1/s, respectively. Results found that, RA showed an obvious increase with the increase in pH, inlet gas concentration and gas temperature, while KGa decreased with an increase in inlet gas concentration. Using linear regression, an empirical expression for KGa/E was obtained. On the other hand, ammonia bicarbonate crystals could be produced at a pH of 9.5 when the gas concentration was higher than 30% and γ (=Fg/FA, the gas-liquid molar flow rate ratio) ≥ 1.5. Full article
(This article belongs to the Special Issue Carbonates)
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Open AccessReview Van der Waals Heterostructure Based Field Effect Transistor Application
Crystals 2018, 8(1), 8; doi:10.3390/cryst8010008
Received: 16 November 2017 / Revised: 18 December 2017 / Accepted: 20 December 2017 / Published: 26 December 2017
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Abstract
Van der Waals heterostructure is formed by two-dimensional materials, which applications have become hot topics and received intensive exploration for fabricating without lattice mismatch. With the sustained decrease in dimensions of field effect transistors, van der Waals heterostructure plays an important role in
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Van der Waals heterostructure is formed by two-dimensional materials, which applications have become hot topics and received intensive exploration for fabricating without lattice mismatch. With the sustained decrease in dimensions of field effect transistors, van der Waals heterostructure plays an important role in improving the performance of devices because of its prominent electronic and optoelectronic behavior. In this review, we discuss the process of assembling van der Waals heterostructures and thoroughly illustrate the applications based on van der Waals heterostructures. We also present recent innovation in field effect transistors and van der Waals stacks, and offer an outlook of the development in improving the performance of devices based on van der Waals heterostructures. Full article
(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)
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Open AccessReview In2O3-Based Thermoelectric Materials: The State of the Art and the Role of Surface State in the Improvement of the Efficiency of Thermoelectric Conversion
Crystals 2018, 8(1), 14; doi:10.3390/cryst8010014
Received: 9 October 2017 / Revised: 1 November 2017 / Accepted: 6 November 2017 / Published: 1 January 2018
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Abstract
In this paper, the thermoelectric properties of In2O3-based materials in comparison with other thermoelectric materials are considered. It is shown that nanostructured In2O3 Sn-based oxides are promising for thermoelectric applications at moderate temperatures. Due to the
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In this paper, the thermoelectric properties of In2O3-based materials in comparison with other thermoelectric materials are considered. It is shown that nanostructured In2O3 Sn-based oxides are promising for thermoelectric applications at moderate temperatures. Due to the nanostructure, specific surface properties of In2O3 and filtering effects, it is possible to significantly reduce the thermal conductivity and achieve an efficiency of thermoelectric conversion inaccessible to bulk materials. It is also shown that a specific surface state at the intergrain boundary, optimal for maximizing the filtering effect, can be achieved through (1) the engineering of grain boundary parameters, (2) controlling the composition of the surrounding atmosphere, and (3) selecting the appropriate operating temperature. Full article
(This article belongs to the Special Issue Semiconductor Nanomaterials Surfaces)
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Open AccessReview Perplexing Coordination Behaviour of Potentially Bridging Bipyridyl-Type Ligands in the Coordination Chemistry of Zinc and Cadmium 1,1-Dithiolate Compounds
Crystals 2018, 8(1), 18; doi:10.3390/cryst8010018
Received: 9 December 2017 / Revised: 29 December 2017 / Accepted: 31 December 2017 / Published: 4 January 2018
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Abstract
The X-ray structural chemistry of zinc and cadmium 1,1-dithiolates (for example, xanthate, dithiophosphate and dithiocarbamate) with potentially bridging bipyridyl-type ligands (for example, 4,4′-bipyridine) is reviewed. For zinc, the xanthates and dithiophosphates uniformly form one-dimensional coordination polymers, whereas the zinc dithiocarbamates are always zero-dimensional,
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The X-ray structural chemistry of zinc and cadmium 1,1-dithiolates (for example, xanthate, dithiophosphate and dithiocarbamate) with potentially bridging bipyridyl-type ligands (for example, 4,4′-bipyridine) is reviewed. For zinc, the xanthates and dithiophosphates uniformly form one-dimensional coordination polymers, whereas the zinc dithiocarbamates are always zero-dimensional, reflecting the exceptional chelating ability of dithiocarbamate ligands compared with xanthates and dithiophosphates. For cadmium, one-dimensional coordination polymers are usually found, reflecting the larger size of cadmium compared with zinc, but zero-dimensional aggregates are sometimes found. Steric effects associated with the 1,1-dithiolate-bound R groups are shown to influence supramolecular aggregation and, when formed, polymer topology in order to reduce steric hindrance; the nature of the bipyridyl-type ligand can also be influential. For the dithiocarbamates of both zinc and cadmium, in instances where the dithiocarbamate ligand is functionalised with hydrogen bonding potential, extended supramolecular architectures are often formed via hydrogen bonding interactions. Of particular interest is the observation that the bipyridyl-type ligands do not always bridge zinc or cadmium 1,1-dithiolates, being monodentate instead, often in the presence of hydrogen bonding. Thus, hydroxyl-O–HN(pyridyl) hydrogen bonds are sometimes formed in preference to M←N(pyridyl) coordinate-bonds, suggesting a competition between the two modes of association. Full article
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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Open AccessReview Introducing Magnetism into 2D Nonmagnetic Inorganic Layered Crystals: A Brief Review from First-Principles Aspects
Crystals 2018, 8(1), 24; doi:10.3390/cryst8010024
Received: 11 November 2017 / Revised: 6 December 2017 / Accepted: 4 January 2018 / Published: 7 January 2018
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Abstract
Pioneering explorations of the two-dimensional (2D) inorganic layered crystals (ILCs) in electronics have boosted low-dimensional materials research beyond the prototypical but semi-metallic graphene. Thanks to species variety and compositional richness, ILCs are further activated as hosting matrices to reach intrinsic magnetism due to
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Pioneering explorations of the two-dimensional (2D) inorganic layered crystals (ILCs) in electronics have boosted low-dimensional materials research beyond the prototypical but semi-metallic graphene. Thanks to species variety and compositional richness, ILCs are further activated as hosting matrices to reach intrinsic magnetism due to their semiconductive natures. Herein, we briefly review the latest progresses of manipulation strategies that introduce magnetism into the nonmagnetic 2D and quasi-2D ILCs from the first-principles computational perspectives. The matrices are concerned within naturally occurring species such as MoS2, MoSe2, WS2, BN, and synthetic monolayers such as ZnO and g-C2N. Greater attention is spent on nondestructive routes through magnetic dopant adsorption; defect engineering; and a combination of doping-absorbing methods. Along with structural stability and electric uniqueness from hosts, tailored magnetic properties are successfully introduced to low-dimensional ILCs. Different from the three-dimensional (3D) bulk or zero-dimensional (0D) cluster cases, origins of magnetism in the 2D space move past most conventional physical models. Besides magnetic interactions, geometric symmetry contributes a non-negligible impact on the magnetic properties of ILCs, and surprisingly leads to broken symmetry for magnetism. At the end of the review, we also propose possible combination routes to create 2D ILC magnetic semiconductors, tentative theoretical models based on topology for mechanical interpretations, and next-step first-principles research within the domain. Full article
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Open AccessReview Switchable Liquid Crystal Contact Lenses for the Correction of Presbyopia
Crystals 2018, 8(1), 29; doi:10.3390/cryst8010029
Received: 15 October 2017 / Revised: 8 January 2018 / Accepted: 9 January 2018 / Published: 12 January 2018
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Abstract
Presbyopia is an age-related disorder where the lens of the eye hardens so that focusing on near objects becomes increasingly difficult. This complaint affects everyone over the age of 50. It is becoming progressively more relevant, as the average age of the global
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Presbyopia is an age-related disorder where the lens of the eye hardens so that focusing on near objects becomes increasingly difficult. This complaint affects everyone over the age of 50. It is becoming progressively more relevant, as the average age of the global population continues to rise. Bifocal or varifocal spectacles are currently the best solution for those that require near and far vision correction. However, many people prefer not to wear spectacles and while multifocal contact lenses are available, they are not widely prescribed and can require significant adaptation by wearers. One possible solution is to use liquid crystal contact lenses that can change focal power by applying a small electric field across the device. However, the design of these contact lenses must be carefully considered as they must be comfortable for the user to wear and able to provide the required change in focal power (usually about +2D). Progress towards different lens designs, which includes lens geometry, liquid crystal choices and suitable alignment modes, are reviewed. Furthermore, we also discuss suitable electrode materials, possible power sources and suggest some methods for switching the lenses between near and far vision correction. Full article
(This article belongs to the Section Liquid Crystals)
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Open AccessReview Study on Dislocation-Dopant Ions Interaction in Ionic Crystals by the Strain-Rate Cycling Test during the Blaha Effect
Crystals 2018, 8(1), 31; doi:10.3390/cryst8010031
Received: 23 October 2017 / Revised: 24 December 2017 / Accepted: 8 January 2018 / Published: 12 January 2018
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Abstract
The interaction between a dislocation and impurities has been investigated by measurements of yield stress and proof stress, micro-hardness tests, direct observations of dislocation, internal friction measurements, or stress relaxation tests so far. A large number of investigations has been carried out by
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The interaction between a dislocation and impurities has been investigated by measurements of yield stress and proof stress, micro-hardness tests, direct observations of dislocation, internal friction measurements, or stress relaxation tests so far. A large number of investigations has been carried out by the separation of the flow stress into effective and internal stresses on the basis of the temperature dependence of yield stress, the strain rate dependence of flow stress, and stress relaxation. Nevertheless, it is difficult to investigate the interaction between a dislocation and obstacles during plastic deformation by the mentioned methods. As for the original method which combines strain-rate cycling tests with the Blaha effect measurement, the original method is different from above-mentioned ones and would be possible to clear it up. The strain-rate cycling test during the Blaha effect measurement has successively provided the information on the dislocation motion breaking away from the strain fields around dopant ions with the help of thermal activation, and seems to separate the contributions arising from the interaction between dislocation and the point defects and those from dislocations themselves during plastic deformation of ionic crystals. Such information on dislocation motion in bulk material cannot be obtained by the widely known methods so far. Furthermore, the various deformation characteristics derived from the original method are sensitive to a change in the state of dopant ions in a specimen by heat treatment, e.g., the Gibbs free energy (G0) for overcoming of the strain field around the dopant by a dislocation at absolute zero becomes small for the annealed KCl:Sr2+ single crystal (G0 = 0.26 eV) in comparison with that for the quenched one (G0 = 0.39 eV). Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessReview Production Methods of Van der Waals Heterostructures Based on Transition Metal Dichalcogenides
Crystals 2018, 8(1), 35; doi:10.3390/cryst8010035
Received: 14 November 2017 / Revised: 11 January 2018 / Accepted: 11 January 2018 / Published: 15 January 2018
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Abstract
Two dimensional (2D) materials have gained significant attention since the discovery of graphene in 2004. Layered transition metal dichalcogenides (TMDs) have become the focus of 2D materials in recent years due to their wide range of chemical compositions and a variety of properties.
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Two dimensional (2D) materials have gained significant attention since the discovery of graphene in 2004. Layered transition metal dichalcogenides (TMDs) have become the focus of 2D materials in recent years due to their wide range of chemical compositions and a variety of properties. These TMDs layers can be artificially integrated with other layered materials into a monolayer (lateral) or a multilayer stack (vertical) heterostructures. The resulting heterostructures provide new properties and applications beyond their component 2D atomic crystals and many exciting experimental results have been reported during the past few years. In this review, we present the various synthesis methods (mechanical exfoliation, physical vapor transport, chemical vapor deposition, and molecular beam epitaxy method) on van der Waals heterostructures based on different TMDs as well as an outlook for future research. Full article
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