Crystals

11 pages, 5300 KiB

Open AccessArticle

Synthesis and Characterization of AlCoCrFeNiNb_x High-Entropy Alloy Coatings by Laser Cladding

by Hui Jiang, Kaiming Han, Dayan Li and Zhiqiang Cao

Crystals 2019, 9(1), 56; https://doi.org/10.3390/cryst9010056 - 20 Jan 2019

Cited by 53 | Viewed by 5712

AlCoCrFeNiNb_x (x in molar ratio x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy (HEA) coatings were manufactured on 304 stainless steel by laser cladding. The constituent phases, microstructures, chemical composition, micro-hardness and wear resistance of the HEA coatings were investigated [...] Read more.

AlCoCrFeNiNb_x (x in molar ratio x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy (HEA) coatings were manufactured on 304 stainless steel by laser cladding. The constituent phases, microstructures, chemical composition, micro-hardness and wear resistance of the HEA coatings were investigated respectively by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), a Vickers hardness tester and a friction/wear testing machine. It was found that an AlCoCrFeNi alloy coating without Nb consisted of body-centered-cubic (BCC) and order BCC (B2) phases, while the AlCoCrFeNiNb_x (x > 0) alloy coatings consisted of BCC, B2 and Laves phases. Microstructures of the AlCoCrFeNiNb_x alloy coatings evolved from equiaxed grain (x = 0) to hypoeutectic (0.25 ≤ x < 0.75), then to full eutectic (x = 0.75), and finally to hypereutectic (x > 0.75). With increasing Nb content, the Vickers hardness values increased. AlCoCrFeNiNb_0.75 alloy coating with a fully eutectic microstructure demonstrated the best wear resistance among the AlCoCrFeNiNb_x (x ≥ 0) alloy coatings. Full article

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18 pages, 9919 KiB

Open AccessArticle

Direct Phasing of Protein Crystals with Non-Crystallographic Symmetry

by Hongxing He, Mengchao Jiang and Wu-Pei Su

Crystals 2019, 9(1), 55; https://doi.org/10.3390/cryst9010055 - 18 Jan 2019

Cited by 4 | Viewed by 4801

Abstract

An iterative projection algorithm proposed previously for direct phasing of high-solvent-content protein crystals is extended to include non-crystallographic symmetry (NCS) averaging. For proper NCS, when the NCS axis is positioned, the molecular envelope can be automatically rebuilt. For improper NCS, when the NCS [...] Read more.

An iterative projection algorithm proposed previously for direct phasing of high-solvent-content protein crystals is extended to include non-crystallographic symmetry (NCS) averaging. For proper NCS, when the NCS axis is positioned, the molecular envelope can be automatically rebuilt. For improper NCS, when the NCS axis and the translation vector are known, the molecular envelope can also be automatically reconstructed. Some structures with a solvent content of around 50% could be directly solved using this ab initio phasing method. Trial calculations are described to illustrate the methodology. Real diffraction data are used and the calculated phases are good for automatic model building. The refinement of approximate NCS parameters is discussed. Full article

(This article belongs to the Special Issue Protein Crystallography)

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9 pages, 410 KiB

Open AccessArticle

Data-Driven Studies of Li-Ion-Battery Materials

by Steven K. Kauwe, Trevor David Rhone and Taylor D. Sparks

Crystals 2019, 9(1), 54; https://doi.org/10.3390/cryst9010054 - 18 Jan 2019

Cited by 46 | Viewed by 7623

Abstract

Batteries are a critical component of modern society. The growing demand for new battery materials—coupled with a historically long materials development time—highlights the need for advances in battery materials development. Understanding battery systems has been frustratingly slow for the materials science community. In [...] Read more.

Batteries are a critical component of modern society. The growing demand for new battery materials—coupled with a historically long materials development time—highlights the need for advances in battery materials development. Understanding battery systems has been frustratingly slow for the materials science community. In particular, the discovery of more abundant battery materials has been difficult. In this paper, we describe how machine learning tools can be exploited to predict the properties of battery materials. In particular, we report the challenges associated with a data-driven investigation of battery systems. Using a dataset of cathode materials and various statistical models, we predicted the specific discharge capacity at 25 cycles. We discuss the present limitations of this approach and propose a paradigm shift in the materials research process that would better allow data-driven approaches to excel in aiding the discovery of battery materials. Full article

(This article belongs to the Special Issue New Materials for Li-Ion Batteries)

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13 pages, 3797 KiB

Open AccessArticle

Simple and Efficient Spherical Crystallization of Clopidogrel Bisulfate Form-I via Anti-Solvent Crystallization Method

by Ji-Hun An, Alice Nguvoko Kiyonga, Eun Hee Lee and Kiwon Jung

Crystals 2019, 9(1), 53; https://doi.org/10.3390/cryst9010053 - 17 Jan 2019

Cited by 8 | Viewed by 6728

Abstract

Clopidogrel bisulfate (CLP) form-I crystals are irregular, rectangular-shaped crystals. Because of their poor compressibility, flowability and their strong surface tension, manufacturers apply spherical crystallization methods to produce CLP form-I spherical agglomerates with a uniform particle size distribution. Consequently, manufacturers primarily synthesize CLP form-I [...] Read more.

Clopidogrel bisulfate (CLP) form-I crystals are irregular, rectangular-shaped crystals. Because of their poor compressibility, flowability and their strong surface tension, manufacturers apply spherical crystallization methods to produce CLP form-I spherical agglomerates with a uniform particle size distribution. Consequently, manufacturers primarily synthesize CLP form-I crystal salts utilizing very complex methods, which produces form-I spherical agglomerates by means of spherical crystallization. In this study, spherical crystals of CLP Form-I were directly prepared from CLP Form-II, the most stable polymorph at room temperature, by using ethanol as solvent and a mixture of isopropyl alcohol (IPA)/n-Hexane (Hex) as an anti-solvent. To provide systematic inputs for the development of spherical agglomerates of optimal morphology, size, particle size distribution (PSD), and polymorphic form, processing parameters such as anti-solvent type, a mixture of IPA/Hex, pure Hex, or pure acetone; stirring speeds of 500, 600, 700, or 800 rpm; and temperatures ranging from 25 to 40 °C were explored. The effects of these parameters on spherical crystallization and polymorphic form were studied in terms of supersaturation, a driving force for polymorphic transformation, and the crystallization solution. Notably, our method does not require a large volume of anti-solvent which is the main complication of conventional anti-solvent crystallization methods. Full article

(This article belongs to the Special Issue Anti-Solvent Crystallization)

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19 pages, 24201 KiB

Open AccessArticle

A Study of the Structural Organization of Water and Aqueous Solutions by Means of Optical Microscopy

by Tatiana Yakhno and Vladimir Yakhno

Crystals 2019, 9(1), 52; https://doi.org/10.3390/cryst9010052 - 17 Jan 2019

Cited by 3 | Viewed by 7442

Abstract

The structural organization of water and aqueous solutions under an optical microscope in a layer with a thickness of 8 μm was investigated. It is shown that under room conditions water (including “ultrapure” water) and aqueous solutions are microdispersed systems. The revealed effect [...] Read more.

The structural organization of water and aqueous solutions under an optical microscope in a layer with a thickness of 8 μm was investigated. It is shown that under room conditions water (including “ultrapure” water) and aqueous solutions are microdispersed systems. The revealed effect does not depend on the properties of the substrate (texture, hydrophilicity/hydrophobicity) and is an inherent property of the liquid. The disperse phase is based on contrasting micron-sized formations located in the center of low-contrast homogeneous spheres observed in a layer with a thickness of the order of the diameter of the observed structures. They form loose millimeter-sized associates in the liquid phase. When the water is boiled, the associates become disordered, but the dispersed phase is preserved. An increase in the ionic strength of the solution is accompanied by coacervation of the dispersed phase. When the liquid part of the water evaporates, the microdispersed phase remains on the substrate. The central particles begin to grow and take on the form of crystals. On the basis of the literature data and their own research, the authors believe that the structures are sodium chloride microcrystals surrounded by a thick layer of hydrated water. Possible ways of salt penetration into the aquatic environment are discussed. Full article

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8 pages, 2851 KiB

Open AccessArticle

Synthesis of Furan-Substituted N-Heteroacene-Based Liquid Material and Its Acid-Recognizing Behavior

by Kyosuke Isoda and Ayumi Ikenaga

Crystals 2019, 9(1), 51; https://doi.org/10.3390/cryst9010051 - 17 Jan 2019

Cited by 10 | Viewed by 3633

Abstract

In this study, we synthesized a novel N-heteroacene-based liquid material 6,7-bis(3,7,11-trimethyl-1-dodecyloxy)-2,3-difurylquinoxaline (RPNL 1), containing two furan rings. We revealed that RPNL 1 adopted a disordered liquid at 25 °C, determined by polarized optical microscopic observation, differential scanning calorimetry, [...] Read more.

In this study, we synthesized a novel N-heteroacene-based liquid material 6,7-bis(3,7,11-trimethyl-1-dodecyloxy)-2,3-difurylquinoxaline (RPNL 1), containing two furan rings. We revealed that RPNL 1 adopted a disordered liquid at 25 °C, determined by polarized optical microscopic observation, differential scanning calorimetry, and X-ray diffraction measurements. The fluorescent spectrum measurement revealed that RPNL 1 showed a blue emission at 25 °C. Dissolving benzene sulfonic acid (BSA) in RPNL 1 brought about dramatic changes in its physical properties, such as emission colors, as well as sample states. Upon recognizing BSA, photoluminescent color was changed into orange, as well as phase transition occurred from liquid to a liquid-crystalline phase. RPNL 1 can function as an acid-recognizing material, accompanied with the color changes in emission. Full article

(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)

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11 pages, 1764 KiB

Open AccessArticle

Tuning the Size, Shape and Density of γ′-Ga_yFe_4−yN Nanocrystals Embedded in GaN

by Andrea Navarro-Quezada, Thibaut Devillers, Tian Li and Alberta Bonanni

Crystals 2019, 9(1), 50; https://doi.org/10.3390/cryst9010050 - 17 Jan 2019

Cited by 6 | Viewed by 3285

Abstract

Phase-separated semiconductor systems hosting magnetic nanocrystal (NCs) are attracting increasing attention, due to their potential as spintronic elements for the next generation of devices. Owing to their morphology- and stoichiometry-dependent magnetic response, self-assembled

γ

’-Ga

_{y}

Fe

_{4 - y}

N NCs embedded [...] Read more.

Phase-separated semiconductor systems hosting magnetic nanocrystal (NCs) are attracting increasing attention, due to their potential as spintronic elements for the next generation of devices. Owing to their morphology- and stoichiometry-dependent magnetic response, self-assembled

γ

’-Ga

_{y}

Fe

_{4 - y}

N NCs embedded in a Fe

δ

-doped GaN matrix, are particularly versatile. It is studied and reported here, how the tuning of relevant growth parameters during the metalorganic vapour phase epitaxy process affects the crystalline arrangement, size, and shape of these self-assembled nanostructures. In particular, it is found that the Ga-flow provided during the

δ

-doping, determines the amount of Fe incorporated into the layers and the spatial density of the NCs. Moreover, the in-plane dimensions of the NCs can also be controlled via the Ga-flow, conditioning the aspect-ratio of the embedded nanostructures. These findings are pivotal for the design of nanocrystal arrays with on-demand size and shape, essential requirements for the implementation into functional devices. Full article

(This article belongs to the Special Issue MOVPE Growth of Crystalline Film)

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10 pages, 4394 KiB

Open AccessArticle

Investigation of Piezoelectric Ringing Frequency Response of Beta Barium Borate Crystals

by Giedrius Sinkevicius and Algirdas Baskys

Crystals 2019, 9(1), 49; https://doi.org/10.3390/cryst9010049 - 17 Jan 2019

Cited by 10 | Viewed by 5073

Abstract

The piezoelectric ringing phenomenon in Pockels cells based on the beta barium borate crystals was analyzed in this work. The investigation results show that piezoelectric ringing is caused by multiple high voltage pulses with a frequency in the range from 10 kHz up [...] Read more.

The piezoelectric ringing phenomenon in Pockels cells based on the beta barium borate crystals was analyzed in this work. The investigation results show that piezoelectric ringing is caused by multiple high voltage pulses with a frequency in the range from 10 kHz up to 1 MHz. Experimental investigation of frequency response and Discrete Fourier transformation was used for analysis. The method of piezoelectric ringing investigation based on the analysis of difference of real and simulated optical signals spectrums was proposed. The investigations were performed for crystals with 3 × 3 × 25 mm, 4 × 4 × 25 mm and 4 × 4 × 20 mm dimensions. It was estimated that piezoelectric ringing in the beta barium borate crystal with dimensions of 3 × 3 mm × 25 mm occurred at the 150, 205, 445, 600 and 750 kHz frequencies of high voltage pulses. Full article

(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)

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15 pages, 1986 KiB

Open AccessArticle

First-Principles Assessment of the Structure and Stability of 15 Intrinsic Point Defects in Zinc-Blende Indium Arsenide

by Qing Peng, Nanjun Chen, Danhong Huang, Eric R. Heller, David A. Cardimona and Fei Gao

Crystals 2019, 9(1), 48; https://doi.org/10.3390/cryst9010048 - 17 Jan 2019

Cited by 5 | Viewed by 6817

Abstract

Point defects are inevitable, at least due to thermodynamics, and essential for engineering semiconductors. Herein, we investigate the formation and electronic structures of fifteen different kinds of intrinsic point defects of zinc blende indium arsenide (zb-InAs ) using first-principles calculations. For [...] Read more.

Point defects are inevitable, at least due to thermodynamics, and essential for engineering semiconductors. Herein, we investigate the formation and electronic structures of fifteen different kinds of intrinsic point defects of zinc blende indium arsenide (zb-InAs ) using first-principles calculations. For As-rich environment, substitutional point defects are the primary intrinsic point defects in zb-InAs until the n-type doping region with Fermi level above 0.32 eV is reached, where the dominant intrinsic point defects are changed to In vacancies. For In-rich environment, In tetrahedral interstitial has the lowest formation energy till n-type doped region with Fermi level 0.24 eV where substitutional point defects In

_{A s}

take over. The dumbbell interstitials prefer

< 110 >

configurations. For tetrahedral interstitials, In atoms prefer 4-As tetrahedral site for both As-rich and In-rich environments until the Fermi level goes above 0.26 eV in n-type doped region, where In atoms acquire the same formation energy at both tetrahedral sites and the same charge state. This implies a fast diffusion along the

t - T - t

path among the tetrahedral sites for In atoms. The In vacancies V

_{I n}

decrease quickly and monotonically with increasing Fermi level and has a

q = - 3 e

charge state at the same time. The most popular vacancy-type defect is V

_{I n}

in an As-rich environment, but switches to V

_{A s}

in an In-rich environment at light p-doped region when Fermi level below 0.2 eV. This study sheds light on the relative stabilities of these intrinsic point defects, their concentrations and possible diffusions, which is expected useful in defect-engineering zb-InAs based semiconductors, as well as the material design for radiation-tolerant electronics. Full article

(This article belongs to the Special Issue First-Principles Prediction of Structures and Properties in Crystals)

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14 pages, 4076 KiB

Open AccessArticle

Research on the High-Performance Electrochemical Energy Storage of a NiO@ZnO (NZO) Hybrid Based on Growth Time

by Jiahong Zheng, Runmei Zhang, Kangkang Cheng, Ziqi Xu, Pengfei Yu, Xingang Wang and Shifeng Niu

Crystals 2019, 9(1), 47; https://doi.org/10.3390/cryst9010047 - 16 Jan 2019

Cited by 15 | Viewed by 4292

Abstract

A NiO@ZnO (NZO) hybrid with different reaction times was successfully synthesized by a green hydrothermal method. After comparison, it was found that hydrothermal time had a great impact on specific capacitance. As a supercapacitor electrode of NZO-12h, it exhibited the maximum reversible specific [...] Read more.

A NiO@ZnO (NZO) hybrid with different reaction times was successfully synthesized by a green hydrothermal method. After comparison, it was found that hydrothermal time had a great impact on specific capacitance. As a supercapacitor electrode of NZO-12h, it exhibited the maximum reversible specific capacitance of 985.0 F/g (3.94 F/cm²) at 5 mA/cm² and 587.5 F/g (2.35 F/cm²) at 50 mA/cm², as well as a high retention of 74.9% capacitance after 1500 cycles at 20 mA/cm². Furthermore, the asymmetric electrode device with ZnO-12h and activated carbon (AC) as the positive and negative electrodes was successfully assembled. In addition, the device exhibited a specific capacitance of 85.7 F/g at 0.4 A/g. Moreover, the highest energy density of 27.13 Wh kg⁻¹ was obtained at a power density of 321.42 W kg⁻¹. These desirable electrochemical properties demonstrate that the NZO hybrid is a promising electrode material for a supercapacitor. Full article

(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)

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18 pages, 3517 KiB

Open AccessEditor’s ChoiceArticle

Spatio-temporal Investigations of the Incomplete Spin Transition in a Single Crystal of [Fe(2-pytrz)₂{Pt(CN)₄}]·3H₂O: Experiment and Theory

by Houcem Fourati, Guillaume Bouchez, Miguel Paez-Espejo, Smail Triki and Kamel Boukheddaden

Crystals 2019, 9(1), 46; https://doi.org/10.3390/cryst9010046 - 16 Jan 2019

Cited by 15 | Viewed by 4114

Abstract

Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz)

_{2}

{Pt(CN)

_{4}

}]·3H

_{2}

O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, [...] Read more.

Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz)

_{2}

{Pt(CN)

_{4}

}]·3H

_{2}

O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, high-spin low-spin (HS-LS) state, below 153 K, where only one of the two crystallographic Fe(II) centers switches from the HS to HS-LS state. In comparison with crystals undergoing a complete spin transition, the present transformation involves smaller volume changes at the transition, which helps to preserving the crystal’s integrity. By analyzing the spatio-temporal properties of this spin transition, we evidenced a direct correlation between the orientation and shape of HS/HS-LS domain wall with the crystal’s shape. Thanks to the small volume change accompanying this spin transition, the analysis of the experimental data by an anisotropic reaction-diffusion model becomes very relevant and leads to an excellent agreement with the experimental observations. Full article

(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)

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12 pages, 2723 KiB

Open AccessArticle

Modification of Structure and Magnetic Properties in Coordination Assemblies Based on [Cu(cyclam)]²⁺ and [W(CN)₈]³⁻

by Aleksandra Pacanowska, Mateusz Reczyński and Beata Nowicka

Crystals 2019, 9(1), 45; https://doi.org/10.3390/cryst9010045 - 16 Jan 2019

Cited by 6 | Viewed by 3785

Abstract

The 1D {[Cu^II(cyclam)]₃[W^V(CN)₈]₂^.5H₂O}_n (1·5H₂O) (cyclam = 1,4,8,11-tetraazacyclotetradecane) coordination polymer of ladder topology can be obtained in water-alcohol solution from [Cu(cyclam)]²⁺ and [W(CN)₈] [...] Read more.

The 1D {[Cu^II(cyclam)]₃[W^V(CN)₈]₂^.5H₂O}_n (1·5H₂O) (cyclam = 1,4,8,11-tetraazacyclotetradecane) coordination polymer of ladder topology can be obtained in water-alcohol solution from [Cu(cyclam)]²⁺ and [W(CN)₈]³⁻ building blocks. Upon dehydration, 1·5H₂O undergoes a single-crystal-to-single-crystal structural transformation to the anhydrous {[Cu^II(cyclam)]₃[W^V(CN)₈]₂}_n (1) form, which retains the same topology, but is characterized by shorter Cu-W distances and significantly more bent CN-bridges. The deformation of the coordination skeleton is reflected in magnetic properties: the predominant intra-chain interactions change from ferromagnetic in 1·5H₂O to antiferromagnetic in 1. The reaction between the same building blocks in water solution under slow diffusion conditions leads to the formation of a 0D {[Cu^II(cyclam)(H₂O)]₂[Cu^II(cyclam)][W^V(CN)₈]₂}^.3H₂O pentanuclear assembly (2·3H₂O). Full article

(This article belongs to the Special Issue Molecular Magnets)

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11 pages, 3273 KiB

Open AccessArticle

Comparative Investigation on the Emission Properties of RAl₃(BO₃)₄ (R = Pr, Eu, Tb, Dy, Tm, Yb) Crystals with the Huntite Structure

by Enrico Cavalli and Nikolay I. Leonyuk

Crystals 2019, 9(1), 44; https://doi.org/10.3390/cryst9010044 - 16 Jan 2019

Cited by 11 | Viewed by 3836

Abstract

The luminescence properties of RAl₃(BO₃)₄ (RAB, with R = Pr, Eu, Tb, Dy, Tm, Yb) huntite crystals grown from K₂Mo₃O₁₀ flux were systematically characterized in order to investigate their excitation dynamics, with particular [...] Read more.

The luminescence properties of RAl₃(BO₃)₄ (RAB, with R = Pr, Eu, Tb, Dy, Tm, Yb) huntite crystals grown from K₂Mo₃O₁₀ flux were systematically characterized in order to investigate their excitation dynamics, with particular reference to the concentration quenching that in these systems is incomplete. To this purpose, selected excitation, emission, and decay profile measurements on diluted R:YAB crystals were carried out and compared with those of the concentrated compounds. The effects of the energy transfer processes and of the lattice defects, as well as the ion-lattice interactions, have been taken into consideration in order to account for the experimental results. Full article

(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)

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15 pages, 7759 KiB

Open AccessArticle

Determination of the Full ²⁰⁷Pb Chemical Shift Tensor of Anglesite, PbSO₄, and Correlation of the Isotropic Shift to Lead–Oxygen Distance in Natural Minerals

by Otto E. O. Zeman, Jennifer Steinadler, Rupert Hochleitner and Thomas Bräuniger

Crystals 2019, 9(1), 43; https://doi.org/10.3390/cryst9010043 - 15 Jan 2019

Cited by 10 | Viewed by 4596

Abstract

The full

^{207}

Pb chemical shift (CS) tensor of lead in the mineral anglesite, PbSO

_{4}

, was determined from orientation-dependent nuclear magnetic resonance (NMR) spectra of a large natural single crystal, using a global fit over two rotation patterns. The resulting tensor [...] Read more.

The full

^{207}

Pb chemical shift (CS) tensor of lead in the mineral anglesite, PbSO

_{4}

, was determined from orientation-dependent nuclear magnetic resonance (NMR) spectra of a large natural single crystal, using a global fit over two rotation patterns. The resulting tensor is characterised by the reduced anisotropy

Δ δ = (- 327 \pm 4)

ppm, asymmetry

η_{C S} = 0.529 \pm 0.002

, and

δ_{i s o} = (- 3615 \pm 3)

ppm, with the isotropic chemical shift

δ_{i s o}

also verified by magic-angle spinning NMR on a polycrystalline sample. The initially unknown orientation of the mounted single crystal was included in the global data fit as well, thus obtaining it from NMR data only. By use of internal crystal symmetries, the amount of data acquisition and processing for determination of the CS tensor and crystal orientation was reduced. Furthermore, a linear correlation between the

^{207}

Pb isotropic chemical shift and the shortest Pb–O distance in the co-ordination sphere of Pb

^{2 +}

solely surrounded by oxygen has been established for a large database of lead-bearing natural minerals. Full article

(This article belongs to the Special Issue NMR Crystallography)

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16 pages, 406 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Crystals in 2018

by Crystals Editorial Office

Crystals 2019, 9(1), 42; https://doi.org/10.3390/cryst9010042 - 15 Jan 2019

Viewed by 3418

Abstract

Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article

13 pages, 309 KiB

Open AccessArticle

Decay Time Estimates by a Continuum Model for Inorganic Scintillators

by Fabrizio Daví

Crystals 2019, 9(1), 41; https://doi.org/10.3390/cryst9010041 - 15 Jan 2019

Cited by 6 | Viewed by 2816

Abstract

We use the phenomenological continuum model for inorganic scintillators proposed by the author to give decay time estimates for four scintillators previously studied, namely NaI:Tl, CaF₂, Gd₂SiO₅Ce (GSO:Ce), and LaCl₃:Ce. We show that, in order [...] Read more.

We use the phenomenological continuum model for inorganic scintillators proposed by the author to give decay time estimates for four scintillators previously studied, namely NaI:Tl, CaF₂, Gd₂SiO₅Ce (GSO:Ce), and LaCl₃:Ce. We show that, in order to obtain a good estimate of the decay time, we need to know (besides other well-known parameters) either the excitation carriers’ mobility or the structure and the parameters of the recombination mechanism. For these four materials, we know the data for the recombination term, whereas we have very scarce information about mobilities. However, we show that also in absence of experimentally-measured mobilities, with reasonable assumptions about them, we can obtain a good estimate for the slow component of the decay time. We show also when it is appropriate to model scintillation with one of the two most-used phenomenological models, the kinetic and the diffusive. The main point of the present approach is that it requires a limited set of experimentally-measured data and can be hopefully used in conjunction with more sophisticated and detailed models to design faster inorganic scintillators. Full article

(This article belongs to the Special Issue Scintillator Crystals: Structure, Characterization and Models for Better Performances)

8 pages, 1396 KiB

Open AccessArticle

Crystal Structure of the Disordered Non-Centrosymmetric Compound Fe_0.43Mo_2.56SbO_9.5

by Sk Imran Ali, Sven Lidin and Mats Johnsson

Crystals 2019, 9(1), 40; https://doi.org/10.3390/cryst9010040 - 15 Jan 2019

Cited by 2 | Viewed by 4029

Abstract

Single crystals of Fe_0.43Mo_2.56SbO_9.5 were obtained by hydrothermal techniques at 230 °C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = [...] Read more.

Single crystals of Fe_0.43Mo_2.56SbO_9.5 were obtained by hydrothermal techniques at 230 °C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = 4.0003(2) Å, b = 7.3355(3) Å, c = 12.6985(6) Å, β = 90°. The crystal structure comprises five crystallographically independent M atoms and one Sb³⁺ atom, M atoms are of two kinds of partially occupied sites Mo⁶⁺ and Fe³⁺. The building blocks consist of [SbO₃O_0.5O_0.5E] octahedra (E = lone electron pair) and [(Mo/Fe)O₆] octahedra. The M = (Mo, Fe) and O atoms are arranged in a distorted hexagonal 2D-net, not the Sb atoms. The distortion of the net and consequently the symmetry reduction results mainly from the location of the Sb atoms. Disorder manifests itself as a splitting of the metal sites and as a consequent shortening of the Mo–Fe distances. Six (Mo/Fe)O₆ octahedra are connected to form a pseudohexagonal channel. The Sb³⁺ atom is displaced from the pseudo-six-fold axis. Full article

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10 pages, 3859 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Tripling the Optical Efficiency of Color-Converted Micro-LED Displays with Funnel-Tube Array

by Fangwang Gou, En-Lin Hsiang, Guanjun Tan, Yi-Fen Lan, Cheng-Yeh Tsai and Shin-Tson Wu

Crystals 2019, 9(1), 39; https://doi.org/10.3390/cryst9010039 - 14 Jan 2019

Cited by 56 | Viewed by 10637

Abstract

Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density [...] Read more.

Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density of color conversion materials. With funnel-tube array, the optical efficiency of the color-converted micro-LED display can be improved by ~3X, while the crosstalk is eliminated. After optimization of the tapper angle, the ambient contrast ratio is also improved due to higher light intensity. Full article

(This article belongs to the Special Issue Advanced LED Solid-State Lighting Optics)

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16 pages, 2453 KiB

Open AccessArticle

Steric Effects of Alkyl Substituents at N-Donor Bidentate Amines Direct the Nuclearity, Bonding and Bridging Modes in Isothiocyanato-Copper(II) Coordination Compounds

by Franz A. Mautner, Roland C. Fischer, Ana Torvisco, Maher M. Henary, Andrew Milner, Hunter DeVillier, Tolga N. V. Karsili, Febee R. Louka and Salah S. Massoud

Crystals 2019, 9(1), 38; https://doi.org/10.3390/cryst9010038 - 13 Jan 2019

Cited by 5 | Viewed by 4187

Abstract

A series of Cu(II)-isothiocyanato coordination compounds derived from sterically hindered N-donor diamines were synthesized and characterized: catena-[Cu(Me₃en)(μ-NCS)(NCS)] (1), catena-[Cu(NEt₂Meen)(μ-NCS)(NCS)] (2), catena-[Cu(N,N,2,2-Me₄pn)(μ-NCS)(NCS)] (3), the [...] Read more.

A series of Cu(II)-isothiocyanato coordination compounds derived from sterically hindered N-donor diamines were synthesized and characterized: catena-[Cu(Me₃en)(μ-NCS)(NCS)] (1), catena-[Cu(NEt₂Meen)(μ-NCS)(NCS)] (2), catena-[Cu(N,N,2,2-Me₄pn)(μ-NCS)(NCS)] (3), the dimeric: [Cu₂(N,N′-isp₂en)₂(µ-NCS)₂(NCS)₂] (4) and the monomeric compound [Cu(N,N′-t-Bu₂en)(NCS)₂] (5), where Me₃en = N,N,N′-trimethylethylenediamine, NEt₂Meen = N,N-diethyl-N′-methylethylenediamine, N,N,2,2-Me₄pn = N,N,2,2-tetramethylpropylenediamine, N,N′-isp₂en = N,N′-diisopropylethylenediamine and N,N′-t-Bu₂en = N,N′-di(tert-butyl)ethylenediamine. The coordination compounds were characterized by elemental microanalyses, IR, and UV–Vis spectroscopy as well as single crystal X-ray crystallography. Density Functional Theory (DFT) was used to evaluate the role of steric effects in compounds 4 and 5 and how this may affect the adaption of a specific geometry, NCS-bonding mode, and the dimensionality of the resulting coordination compound. Full article

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27 pages, 6848 KiB

Open AccessArticle

Structure and Magnetic Properties of Bulk Synthesized Mn_2−xFe_xP_1−ySi_y Compounds from Magnetization, ⁵⁷Fe Mössbauer Spectroscopy, and Electronic Structure Calculations

by Daniel Fruchart, Sonia Haj-Khlifa, Patricia de Rango, Mohamed Balli, Ryszard Zach, Wieslaw Chajec, Piotr Fornal, Jan Stanek, Stanislaw Kaprzyk and Janusz Tobola

Crystals 2019, 9(1), 37; https://doi.org/10.3390/cryst9010037 - 13 Jan 2019

Cited by 12 | Viewed by 4199

Abstract

The series of Mn_2−xFe_xP_1−ySi_y types of compounds form one of the most promising families of magnetocaloric materials in term of performances and availability of the elemental components. Potential for large scale application needs to optimize the [...] Read more.

The series of Mn_2−xFe_xP_1−ySi_y types of compounds form one of the most promising families of magnetocaloric materials in term of performances and availability of the elemental components. Potential for large scale application needs to optimize the synthesis process, and an easy and rather fast process here described is based on the use of two main type of precursors, providing the Fe-P and Mn-Si proportions. The series of Mn_2−xFe_xP_1−ySi_y compounds were synthesized and carefully investigated for their crystal structure versus temperature and compared interestingly with earlier results. A strong magnetoelastic effect accompanying the 1st order magnetic transition—as well as the parent phosphide–arsenides—was related to the relative stability of both the Fe magnetic polarization and the Fe–Fe exchange couplings. In order to better understand this effect, we propose a local distortion index of the non-metal tetrahedron hosting Fe atoms. Besides, from Mn-rich (Si-rich) to Fe-rich (P-rich) compositions, it is shown that the magnetocaloric phenomenon can be established on demand below and above room temperature. Excellent performance compounds were realized in terms of magnetic entropy ΔS_m and adiabatic temperature ΔT_ad variations. Since from literature it was seen that the magnetic performances are very sensitive to the synthesis process, correspondingly here a new effective process is proposed. Mössbauer spectroscopy analysis was performed on Mn-rich, equi-atomic Mn-Fe, and Fe-rich compounds, allowing determination of the distribution of hyperfine fields setting on Fe in the tetrahedral and pyramidal sites, respectively. Electronic structure calculations confirmed the scheme of metal and non-metal preferential ordering, respectively. Moreover, the local magnetic moments were derived, in fair agreement with both the experimental magnetization and the Fe contributions, as determined by Mössbauer spectroscopy. Full article

(This article belongs to the Special Issue Advances in Caloric Materials)

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22 pages, 5452 KiB

Open AccessArticle

On the Nature of Luminescence Thermochromism of Multinuclear Copper(I) Benzoate Complexes in the Crystalline State

by Katarzyna N. Jarzembska, Michał Hapka, Radosław Kamiński, Wojciech Bury, Sylwia E. Kutniewska, Dariusz Szarejko and Małgorzata M. Szczęśniak

Crystals 2019, 9(1), 36; https://doi.org/10.3390/cryst9010036 - 12 Jan 2019

Cited by 8 | Viewed by 5641

Abstract

A model luminescent [(PhCO₂)₄Cu₄] (Cu₄) complex in the crystalline state was investigated via combined crystallographic and spectroscopic techniques contributed substantially by theoretical modelling. The complex appeared to exhibit luminescence thermochromism, i.e., red phosphorescence at [...] Read more.

A model luminescent [(PhCO₂)₄Cu₄] (Cu₄) complex in the crystalline state was investigated via combined crystallographic and spectroscopic techniques contributed substantially by theoretical modelling. The complex appeared to exhibit luminescence thermochromism, i.e., red phosphorescence at room temperature which changes to green when lowering the temperature to 90 K. The low-energy emissive state was assigned as a cluster-centred triplet, ³CC. The emission from this state predicted in TDDFT (~635 nm) matches the experimental red band observed at 660–715 nm. In contrast, the nature of the high-energy “green” band was less straightforward. The next reached cluster-centred triplet excited state occurred to be energetically close to the experimental value of ~545 nm. The two excited states also exhibit significant metal-to-ligand and ligand-to-metal charge transfer characteristics, especially for solid-state distorted geometries. In both cases the cluster core was expected to become notably contracted when compared to the ground state. Time-resolved photocrystallographic results supported the computationally predicted core contraction upon excitation. Additionally, the differences between the spectroscopic behaviour of the related tetra- and hexanuclear copper(I) complexes, Cu₄ and Cu₆ (i.e., [(PhCO₂)₆Cu₆]) in the crystalline state were discussed and examined. It appeared that crystal packing may constitute an important factor as far as the lack of luminescence thermochromism in the latter case is concerned. Synopsis: Structure–property relationships characterising a model luminescent [(PhCO₂)₄Cu₄] (Cu₄) complex in the crystalline state were investigated via combined crystallographic and spectroscopic techniques contributed by theoretical modelling, and compared with the properties of the related [(PhCO₂)₆Cu₆] (Cu₆) complex. Full article

(This article belongs to the Special Issue Photocrystallography and Solid-State Structural Dynamics)

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14 pages, 3140 KiB

Open AccessArticle

A Facile and Eco-Friendly Method for the Synthesis of Sulfonamide and Sulfonate Carboxylic Acid Derivatives—X-ray Structure, Hirshfeld Analysis and Spectroscopic Characterizations

by Zainab Almarhoon, Saied M. Soliman, Hazem A. Ghabbour and Ayman El-Faham

Crystals 2019, 9(1), 35; https://doi.org/10.3390/cryst9010035 - 11 Jan 2019

Cited by 12 | Viewed by 5615

Abstract

The search for a simple and efficient method for the synthesis of sulfonamide and sulfonate derivatives under mild and eco-friendly conditions is of continuing interest. Sulfonyl chlorides are still the best choice as starting materials for the preparation of target products. Here, we [...] Read more.

The search for a simple and efficient method for the synthesis of sulfonamide and sulfonate derivatives under mild and eco-friendly conditions is of continuing interest. Sulfonyl chlorides are still the best choice as starting materials for the preparation of target products. Here, we report a simple, efficient and eco-friendly method for the synthesis of sulfonamide and sulfonate carboxylic acid derivatives under green conditions using water and sodium carbonate as HCl scavengers to produce the products with high yields and purities. Two derivatives, 4-(tosyloxy)benzoic acid (5a) and 4-((4-methylphenyl)sulfonamido)benzoic acid (5b), were reacted with 2-morpholinoethan-1-amine under green conditions, where OxymaPure/diisopropylcarbodiimide (DIC) was used as a coupling reagent and 2-MeTHF as a solvent to give the target product with high yield and purity. nuclear magnetic resonance (NMR) and elemental analysis confirmed the structures of all obtained products. X-ray crystallography confirmed the structures of products 4b, 4c and 7a. The molecular packing of the three compounds (4b, 4c and 7a) was analyzed using Hirshfeld topology analysis. Mainly, H…O hydrogen bonding interactions dominated the packing. These methods of preparation and coupling merit further attention for the development of new derivatives that might have significant biological applications. Full article

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13 pages, 2061 KiB

Open AccessCommunication

Substituted Azolium Disposition: Examining the Effects of Alkyl Placement on Thermal Properties

by Karel Goossens, Lena Rakers, Tae Joo Shin, Roman Honeker, Christopher W. Bielawski and Frank Glorius

Crystals 2019, 9(1), 34; https://doi.org/10.3390/cryst9010034 - 11 Jan 2019

Cited by 4 | Viewed by 3884

Abstract

We describe the thermal phase characteristics of a series of 4,5-bis(n-alkyl)azolium salts that were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), and synchrotron-based small- to wide-angle X-ray scattering (SWAXS) measurements. Key results were obtained for [...] Read more.

We describe the thermal phase characteristics of a series of 4,5-bis(n-alkyl)azolium salts that were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), and synchrotron-based small- to wide-angle X-ray scattering (SWAXS) measurements. Key results were obtained for 1,3-dimethyl-4,5-bis(n-undecyl)imidazolium iodide (1-11), 1,3-dimethyl-4,5-bis(n-pentadecyl)imidazolium iodide (1-15), and 1,2,3-trimethyl-4,5-bis(n-pentadecyl)imidazolium iodide (2), which were found to adopt enantiotropic smectic A mesophases. Liquid-crystalline mesophases were not observed for 1,3-dimethyl-4,5-bis(n-heptyl)imidazolium iodide (1-7), 3-methyl-4,5-bis(n-pentadecyl)thiazolium iodide (3), and 2-amino-4,5-bis(n-pentadecyl)imidazolium chloride (4). Installing substituents in the 4- and 5-positions of the imidazolium salts appears to increase melting points while lowering clearing points when compared to data reported for 1,3-disubstituted analogues. Full article

(This article belongs to the Special Issue Ionic Liquid Crystals)

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9 pages, 1846 KiB

Open AccessArticle

On Plowing Frictional Behavior during Scratch Testing: A Comparison between Experimental and Theoretical/Numerical Results

by Per-Lennart Larsson

Crystals 2019, 9(1), 33; https://doi.org/10.3390/cryst9010033 - 11 Jan 2019

Cited by 2 | Viewed by 2980

Abstract

Scratch testing is a contact mechanics based nondestructive testing method that, if correctly evaluated, can give a lot of information about the material and tribological behavior of a material. In contrast to the situation with another contact-based method, indentation testing, wear characteristics can [...] Read more.

Scratch testing is a contact mechanics based nondestructive testing method that, if correctly evaluated, can give a lot of information about the material and tribological behavior of a material. In contrast to the situation with another contact-based method, indentation testing, wear characteristics can also be investigated, for example. In order to get results of practical importance from a scratch test, it is necessary to have evaluation formulae available. Indeed, such formulae exist for scratch testing but can be substantially influenced by frictional effects. For this reason, closed-form analytical relations have been suggested for the purpose of accounting for such effects during scratching and in particular the plowing frictional effect. As a major benefit, these relations can also be of assistance during material characterization through scratch testing. However, the proposed existing relations are based solely on theoretical/numerical analyses and, remembering that the scratch test of course is an experimental approach, verification by experiments is a necessity. Such a task is performed in the present study and it is shown that, based on standard contact global properties, the relations are accurate for most polymeric materials but could also be used for some metallic ones. Full article

(This article belongs to the Special Issue Microstructure Evolutions and Mechanical Behavior of Semicrystalline Polymers)

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9 pages, 3006 KiB

Open AccessArticle

Single Crystal Diamond Deposited by Dual Radio-Frequency Plasma Jet CVD with High Growth Rate

by Hao Liu, Jia-jun Li, Zhen-rui Li, Kai Xu, Zheng-jia Chen and Guang-chao Chen

Crystals 2019, 9(1), 32; https://doi.org/10.3390/cryst9010032 - 10 Jan 2019

Cited by 9 | Viewed by 6075

Abstract

Single crystal diamonds were deposited on high pressure high temperature (HPHT) substrate with high growth rate, up to 18.5 μm/h, by using dual radio-frequency inductive coupled plasma jet. The methane flux was found to influence the growth rate of single crystal diamond. The [...] Read more.

Single crystal diamonds were deposited on high pressure high temperature (HPHT) substrate with high growth rate, up to 18.5 μm/h, by using dual radio-frequency inductive coupled plasma jet. The methane flux was found to influence the growth rate of single crystal diamond. The reason for this might be ascribed to the electron temperature increase, raising the flux of methane, based on the plasma diagnosis results by optical emission spectra (OES). The results of Raman spectroscopy and the X-ray rocking-curve indicated that as-deposited diamonds are of good quality. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Diamond Crystals)

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12 pages, 3257 KiB

Open AccessArticle

Synthesis of NiMoO₄/3D-rGO Nanocomposite in Alkaline Environments for Supercapacitor Electrodes

by Shahrzad Arshadi Rastabi, Rasoul Sarraf Mamoory, Fatemeh Dabir, Nicklas Blomquist, Manisha Phadatare and Håkan Olin

Crystals 2019, 9(1), 31; https://doi.org/10.3390/cryst9010031 - 9 Jan 2019

Cited by 19 | Viewed by 4898

Abstract

Although Graphene oxide (GO)-based materials is known as a favorable candidate for supercapacitors, its conductivity needs to be increased. Therefore, this study aimed to investigate the performance of GO-based supercapicitor with new methods. In this work, an ammonia solution has been used to [...] Read more.

Although Graphene oxide (GO)-based materials is known as a favorable candidate for supercapacitors, its conductivity needs to be increased. Therefore, this study aimed to investigate the performance of GO-based supercapicitor with new methods. In this work, an ammonia solution has been used to remove the oxygen functional groups of GO. In addition, a facile precipitation method was performed to synthesis a NiMoO₄/3D-rGO electrode with purpose of using synergistic effects of rGO conductivity properties as well as NiMoO₄ pseudocapacitive behavior. The phase structure, chemical bands and morphology of the synthesized powders were investigated by X-ray diffraction (XRD), Raman spectroscopy, and field emission secondary electron microscopy (FE-SEM). The electrochemical results showed that the NiMoO₄/3D-rGO(II) electrode, where ammonia has been used during the synthesis, has a capacitive performance of 932 Fg⁻¹. This is higher capacitance than NiMoO₄/3D-rGO(I) without using ammonia. Furthermore, the NiMoO₄/3D-rGO(II) electrode exhibited a power density of up to 17.5 kW kg⁻¹ and an energy density of 32.36 Wh kg⁻¹. These results showed that ammonia addition has increased the conductivity of rGO sheets, and thus it can be suggested as a new technique to improve the capacitance. Full article

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18 pages, 3126 KiB

Open AccessArticle

Bis(triphenylphosphine)iminium Salts of Dioxothiadiazole Radical Anions: Preparation, Crystal Structures, and Magnetic Properties

by Paweł Pakulski, Mirosław Arczyński and Dawid Pinkowicz

Crystals 2019, 9(1), 30; https://doi.org/10.3390/cryst9010030 - 7 Jan 2019

Cited by 5 | Viewed by 5588

Abstract

Phenanthroline dioxothiadiazoles are redox active molecules that form stable radical anions suitable for the construction of supramolecular magnetic materials. Herein, the preparation, structures and magnetic properties of bis(triphenylphosphine)iminium (PPN) salts of [1,2,5]thiadiazole[3,4-f][1,10]phenanthroline 1,1-dioxide (L), [1,2,5]thiadiazole[3,4-f][4,7]phenanthroline 1,1-dioxide (4,7-L), 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide [...] Read more.

Phenanthroline dioxothiadiazoles are redox active molecules that form stable radical anions suitable for the construction of supramolecular magnetic materials. Herein, the preparation, structures and magnetic properties of bis(triphenylphosphine)iminium (PPN) salts of [1,2,5]thiadiazole[3,4-f][1,10]phenanthroline 1,1-dioxide (L), [1,2,5]thiadiazole[3,4-f][4,7]phenanthroline 1,1-dioxide (4,7-L), 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (BrL), and 5,10-dibromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (diBrL) are reported. The preparation of new bromo derivatives of the L: 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (BrL) and 5,10-dibromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (diBrL)—suitable starting materials for further derivatization—are described starting from a commercially available and cheap 1,10-phenanthroline. All PPN salts show antiferromagnetic interactions between the pairs of radical anions, which in the case of PPN(diBrL) are very strong (−116 cm⁻¹; using Ĥ = −2JSS type of exchange coupling Hamiltonian) due to a different crystal packing of the anion radicals as compared to PPN(L), PPN(4,7-L), and PPN(BrL). Full article

(This article belongs to the Special Issue Molecular Magnets)

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10 pages, 3502 KiB

Open AccessArticle

Bismuth-Based Oxyborate Piezoelectric Crystals: Growth and Electro-Elastic Properties

by Feifei Chen, Xiufeng Cheng, Fapeng Yu, Chunlei Wang and Xian Zhao

Crystals 2019, 9(1), 29; https://doi.org/10.3390/cryst9010029 - 6 Jan 2019

Cited by 8 | Viewed by 3859

Abstract

The non-centrosymmetric bismuth-based oxyborate crystals have been extensively studied for non-linear optical, opto-electric and piezoelectric applications. In this work, single crystal growth and electro-elastic properties of α-BiB₃O₆ (α-BIBO) and Bi₂ZnB₂O₇ (BZBO) crystals are reported. Centimeter-sized [...] Read more.

The non-centrosymmetric bismuth-based oxyborate crystals have been extensively studied for non-linear optical, opto-electric and piezoelectric applications. In this work, single crystal growth and electro-elastic properties of α-BiB₃O₆ (α-BIBO) and Bi₂ZnB₂O₇ (BZBO) crystals are reported. Centimeter-sized α-BIBO and BZBO crystals were grown by using the Kyropoulos method. High resolution X-ray diffraction tests were performed to assess the crystal quality. The full-width at half-maximum values (FWHM) of the rocking curves were evaluated to be 35.35 arcsec and 47.85 arcsec for α-BIBO and BZBO samples, respectively. Moreover, the electro-elastic properties of α-BIBO and BZBO crystals are discussed and summarized, based on which the radial extensional and the face shear vibration modes were studied for potential acoustic device applications. The radial extensional mode electro-mechanical coupling factors k_p were evaluated and found to be 32.0% and 5.5% for α-BIBO and BZBO crystals, respectively. The optimal crystal cuts with face shear mode were designed and found to be (YZt)/−53° (or (YZt)/37° cut) for α-BIBO crystal, and (ZXt)/±45° cut for BZBO crystal, with the largest effective piezoelectric coefficients being in the order of 14.8 pC/N and 8.9 pC/N, respectively. Full article

(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)

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11 pages, 4525 KiB

Open AccessArticle

BaWO₄:Ce Single Crystals Codoped with Na Ions

by Slawomir M. Kaczmarek, Grzegorz Leniec, Tomasz Bodziony, Hubert Fuks, Zbigniew Kowalski, Winicjusz Drozdowski, Marek Berkowski, Michal Głowacki, Marcin E. Witkowski and Michal Makowski

Crystals 2019, 9(1), 28; https://doi.org/10.3390/cryst9010028 - 4 Jan 2019

Cited by 7 | Viewed by 4252

Abstract

Single crystals of BaWO₄, BaWO₄: 0.5 at. % Ce; BaWO₄: 1 at. % Ce; BaWO₄: 0.5 at. % Ce, 1 at. % Na; and BaWO₄: 1 at. % Ce, 2 at. % Na [...] Read more.

Single crystals of BaWO₄, BaWO₄: 0.5 at. % Ce; BaWO₄: 1 at. % Ce; BaWO₄: 0.5 at. % Ce, 1 at. % Na; and BaWO₄: 1 at. % Ce, 2 at. % Na were grown from an inductively heated iridium crucible by the Czochralski method on a Malvern MSR4 puller. They were investigated using Electron Paramagnetic Resonance (EPR) spectroscopy at helium temperatures. One isolated center of high (D_2d or S₄) symmetry was found and two or more other centers of lower symmetry were identified, depending on crystal doping. From the fitting using the EPR-NMR program, the following parameters of g-matrix for the high symmetry center were found: g_x = 1.505, g_y = 1.505, and g_z = 2.731. The linewidth vs. temperature revealed an increasing exponential tendency with increasing temperature. It showed one phonon at the lower temperatures and a Raman + Orbach effect at the higher temperatures. Radioluminescence and pulse height spectra showed rather poor scintillation properties, without any contribution from cerium emission. Full article

(This article belongs to the Section Crystal Engineering)

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13 pages, 4075 KiB

Open AccessReview

Ion Irradiation for Planar Patterning of Magnetic Materials

by Takeshi Kato, Daiki Oshima and Satoshi Iwata

Crystals 2019, 9(1), 27; https://doi.org/10.3390/cryst9010027 - 4 Jan 2019

Cited by 10 | Viewed by 3966

Abstract

Kr⁺ ion dose dependence of the magnetic properties of MnGa films and the fabrication of planar-patterned MnGa films by the local ion irradiation technique were reviewed. The magnetization and perpendicular anisotropy of the MnGa vanished at an ion dose of 1 × [...] Read more.

Kr⁺ ion dose dependence of the magnetic properties of MnGa films and the fabrication of planar-patterned MnGa films by the local ion irradiation technique were reviewed. The magnetization and perpendicular anisotropy of the MnGa vanished at an ion dose of 1 × 10¹⁴ ions/cm² due to the phase change of the MnGa from ferromagnetic L1₀ to paramagnetic A1 phase. The average switching field H_sw of the planar-patterned MnGa increased with decreasing the bit size, implying low bit edge damage in the patterned MnGa, whereas a rather large switching field distribution (SFD) of 25% was confirmed for a bit size of ~40 nm. Time resolved magneto-optical Kerr effect measurements revealed that as-prepared MnGa exhibits an effective anisotropy field H_keff = 20 kOe, its distribution ΔH_keff = 200 Oe, and Gilbert damping α = 0.008. The ion-irradiated MnGa films exhibited larger H_keff = 22–23 kOe than that of the MnGa before the ion dose. Thus, ion irradiation does not decrease the perpendicular anisotropy, which suggests a small bit edge in the patterned MnGa. ΔH_keff increased from 0.2 kOe to 3 kOe, whereas the length of disorder in the film ξ decreased from 10 nm to 3 nm by ion irradiation. Full article

(This article belongs to the Special Issue Spin-dependent Optical, Plasmonic, Confinement and High-frequency Phenomena and Applications—Mini-symposium, ETOPIM11)

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