Crystals

20 pages, 3408 KiB

Open AccessEditor’s ChoiceReview

Liquid Crystal Thermography in Gas Turbine Heat Transfer: A Review on Measurement Techniques and Recent Investigations

by Srinath V. Ekkad and Prashant Singh

Crystals 2021, 11(11), 1332; https://doi.org/10.3390/cryst11111332 - 31 Oct 2021

Cited by 20 | Viewed by 4359

Liquid Crystal Thermography is a widely used experimental technique in the gas turbine heat transfer community. In turbine heat transfer, determination of the convective heat transfer coefficient (h) and adiabatic film cooling effectiveness (η) is imperative in order to [...] Read more.

Liquid Crystal Thermography is a widely used experimental technique in the gas turbine heat transfer community. In turbine heat transfer, determination of the convective heat transfer coefficient (h) and adiabatic film cooling effectiveness (η) is imperative in order to design hot gas path components that can meet the modern-day engine performance and emission goals. LCT provides valuable information on the local surface temperature, which is used in different experimental methods to arrive at the local h and η. The detailed nature of h and η through LCT sets it apart from conventional thermocouple-based measurements and provides valuable insights into cooling designers for concept development and its further iterations. This article presents a comprehensive review of the state-of-the-art experimental methods employing LCT, where a critical analysis is presented for each, as well as some recent investigations (2016–present) where LCT was used. The goal of this article is to familiarize researchers with the evolving nature of LCT given the advancements in instrumentation and computing capabilities, and its relevance in turbine heat transfer problems in current times. Full article

(This article belongs to the Special Issue Liquid Crystal Thermography for Gas Turbine Heat Transfer Measurements)

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9 pages, 1755 KiB

Open AccessEditor’s ChoiceArticle

Potential of Sub-THz-Wave Generation in Li₂B₄O₇ Nonlinear Crystal at Room and Cryogenic Temperatures

by Dmitry Ezhov, Snezhana Turgeneva, Nazar Nikolaev, Alexander Mamrashev, Sergei Mikerin, Fedor Minakov, Andrey Simanchuk, Valery Antsygin, Valery Svetlichnyi, Valery Losev and Yury Andreev

Crystals 2021, 11(11), 1321; https://doi.org/10.3390/cryst11111321 - 29 Oct 2021

Cited by 3 | Viewed by 2541

Abstract

Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz [...] Read more.

Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz optical properties of the lithium tetraborate crystal (Li₂B₄O₇; LB4) at 295 and 77 K. Approximating the terahertz refractive index in the form of Sellmeier’s equations, we assessed the possibility of converting the radiation of widespread high-power laser sources with wavelengths of 1064 and 800 nm, as well as their second and third harmonics, into the THz range. It was found that four out of eight types of three-wave mixing processes are possible. The conditions for collinear phase matching were fulfilled only for the o − e → o type of interaction, while cooling the crystal to 77 K did not practically affect the phase-matching curves. However, a noticeable increase of birefringence in the THz range with cooling (from 0.12 to 0.16) led to an increase in the coherence length for o − o → e and e − e → e types of interaction, which are potentially attractive for the down-conversion of ultrashort laser pulses. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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14 pages, 5993 KiB

Open AccessEditor’s ChoiceArticle

Novel Device and Strategy for Growing Large, High-Quality Protein Crystals by Controlling Crystallization Conditions

by Naoki Tanigawa, Sachiko Takahashi, Bin Yan, Masayuki Kamo, Naoki Furubayashi, Koji Kubota, Koji Inaka and Hiroaki Tanaka

Crystals 2021, 11(11), 1311; https://doi.org/10.3390/cryst11111311 - 27 Oct 2021

Cited by 1 | Viewed by 2769

Abstract

Neutron diffraction experiments are informative for determining the locations of hydrogen atoms in protein molecules; however, much larger crystals are needed than those required for X-ray diffraction. Thus, additional techniques are required to grow larger crystals. Here, a unique crystallization device and strategy [...] Read more.

Neutron diffraction experiments are informative for determining the locations of hydrogen atoms in protein molecules; however, much larger crystals are needed than those required for X-ray diffraction. Thus, additional techniques are required to grow larger crystals. Here, a unique crystallization device and strategy for growing large protein crystals are introduced. The device uses two micropumps to control crystal growth by altering the precipitant concentration and regulating the pinpoint injection of dry air flow to the crystallization cell. Furthermore, the crystal growth can be observed in real time. Preliminary microbatch crystallization experiments at various concentration ranges of polyethylene glycol (PEG) 4000 and sodium chloride were first performed to elucidate optimized crystallization conditions. Based on these results, a device to precisely control the sodium chloride and PEG concentrations and the supply of dry air to the crystallization cell was used, and 1.8 mm lysozyme and 1.5 mm alpha-amylase crystals with good reproducibility were obtained. X-ray data sets of both crystals were collected at room temperature at BL2S1 of the Aichi Synchrotron Radiation Center and confirmed that these crystals were of high quality. Therefore, this crystallization device and strategy were effective for growing large, high-quality protein crystals. Full article

(This article belongs to the Special Issue Protein Crystallography: Achievements and Challenges)

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10 pages, 3711 KiB

Open AccessEditor’s ChoiceArticle

Synthesis, Crystal Structure, and Luminescent Properties of a New Holmium(III) Coordination Polymer Involving 2,5-Dihydroxy-1,4-terephthalic Acid Dianion as Ligand

by Jiaqi Li, Linan Dun, Fanming Zeng, Chun Li and Zhongmin Su

Crystals 2021, 11(11), 1294; https://doi.org/10.3390/cryst11111294 - 26 Oct 2021

Cited by 2 | Viewed by 2814

Abstract

A novel coordination polymer {[Ho₂(DHTA)₃(H2O)₅]·H₂O}n (1) was synthesized by hydrothermal synthesis (DHTA = 2,5-dihydroxy-1,4-terephthalic acid anion). The crystallographic data show that complex 1 crystallizes in a triclinic system with space group P [...] Read more.

A novel coordination polymer {[Ho₂(DHTA)₃(H2O)₅]·H₂O}n (1) was synthesized by hydrothermal synthesis (DHTA = 2,5-dihydroxy-1,4-terephthalic acid anion). The crystallographic data show that complex 1 crystallizes in a triclinic system with space group P

\bar{1}

, with a = 9.6617(17) Å, b = 11.902(2) Å, c = 13.284(2) Å, α = 100.617(3)°, β = 92.765(2)°, γ = 106.715(2)°, V = 1429.6(4) Å3, Z = 2, C₂₄H₂₄O₂₄Ho₂, and M_r = 1026.290. Complex 1 contains two eight-coordinated metal centers Ho(III). The TGA results show that the weight loss can be ascribed to the removal of the organic component from 400 to 650 °C. At the temperature above 650 °C, the residue is Holmium(III) oxide (Ho₂O₃). The luminescent results reveal that the complex has potential application as a new green luminescence material. Full article

(This article belongs to the Special Issue Self-Assembled Complexes: “Love at First Sight”)

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14 pages, 3843 KiB

Open AccessEditor’s ChoiceArticle

Photosensitive Bent-Core Liquid Crystals with Laterally Substituted Azobenzene Unit

by Diana Jágerová, Michal Šmahel, Anna Poryvai, Jan Macháček, Vladimíra Novotná and Michal Kohout

Crystals 2021, 11(10), 1265; https://doi.org/10.3390/cryst11101265 - 18 Oct 2021

Cited by 6 | Viewed by 3221

Abstract

Photosensitive liquid crystals represent an important class of functional materials that experience rapid development. Hereby, we present novel bent-core liquid crystals bearing a lateral substitution on the central core and in the vicinity of the photosensitive unit—an azo group. The azo group enables [...] Read more.

Photosensitive liquid crystals represent an important class of functional materials that experience rapid development. Hereby, we present novel bent-core liquid crystals bearing a lateral substitution on the central core and in the vicinity of the photosensitive unit—an azo group. The azo group enables fast (E)-to-(Z)-isomerization upon irradiation with UV-light and visible light, while the substitution facilitates the high stability of the photochemically formed (Z)-isomer. The effectiveness of the irradiation and the composition of photostationary states was determined by UV/Vis and ¹H NMR spectroscopy. A nematic phase formed by the materials was characterized by differential scanning calorimetry and optical polarizing microscopy. We show that the materials easily change their relative configuration of the N=N double bond not only in solution, but also in the mesophase, which leads to fast isothermal phase transition from the nematic phase to isotropic liquid. Full article

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

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9 pages, 7986 KiB

Open AccessEditor’s ChoiceArticle

The Curled Up Dimension in Quasicrystals

by Fang Fang, Richard Clawson and Klee Irwin

Crystals 2021, 11(10), 1238; https://doi.org/10.3390/cryst11101238 - 14 Oct 2021

Viewed by 3678

Abstract

Most quasicrystals can be generated by the cut-and-project method from higher dimensional parent lattices. In doing so they lose the periodic order their parent lattice possess, replaced with aperiodic order, due to the irrationality of the projection. However, perfect periodic order is discovered [...] Read more.

Most quasicrystals can be generated by the cut-and-project method from higher dimensional parent lattices. In doing so they lose the periodic order their parent lattice possess, replaced with aperiodic order, due to the irrationality of the projection. However, perfect periodic order is discovered in the perpendicular space when gluing the cut window boundaries together to form a curved loop. In the case of a 1D quasicrystal projected from a 2D lattice, the irrationally sloped cut region is bounded by two parallel lines. When it is extrinsically curved into a cylinder, a line defect is found on the cylinder. Resolving this geometrical frustration removes the line defect to preserve helical paths on the cylinder. The degree of frustration is determined by the thickness of the cut window or the selected pitch of the helical paths. The frustration can be resolved by applying a shear strain to the cut-region before curving into a cylinder. This demonstrates that resolving the geometrical frustration of a topological change to a cut window can lead to preserved periodic order. Full article

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29 pages, 24863 KiB

Open AccessEditor’s ChoiceArticle

Strain Localization Modes within Single Crystals Using Finite Deformation Strain Gradient Crystal Plasticity

by Lei Cai, Mohamed Jebahi and Farid Abed-Meraim

Crystals 2021, 11(10), 1235; https://doi.org/10.3390/cryst11101235 - 13 Oct 2021

Cited by 5 | Viewed by 2743

Abstract

The present paper aims at providing a comprehensive investigation of the abilities and limitations of strain gradient crystal plasticity (SGCP) theories in capturing different kinds of localization modes in single crystals. To this end, the small deformation Gurtin-type SGCP model recently proposed by [...] Read more.

The present paper aims at providing a comprehensive investigation of the abilities and limitations of strain gradient crystal plasticity (SGCP) theories in capturing different kinds of localization modes in single crystals. To this end, the small deformation Gurtin-type SGCP model recently proposed by the authors, based on non-quadratic defect energy and the uncoupled dissipation assumption, is extended to finite deformation. The extended model is then applied to simulate several single crystal localization problems with different slip system configurations. These configurations are chosen in such a way as to obtain idealized slip and kink bands as well as general localization bands, i.e., with no particular orientation with respect to the initial crystallographic directions. The obtained results show the good abilities of the applied model in regularizing various kinds of localization bands, except for idealized slip bands. Finally, the model is applied to reproduce the complex localization behavior of single crystals undergoing single slip, where competition between kink and slip bands can take place. Both higher-order energetic and dissipative effects are considered in this investigation. For both effects, mesh-independent results are obtained, proving the good capabilities of SGCP theories in regularizing complex localization behaviors. The results associated with higher-order energetic effects are in close agreement with those obtained using a micromorphic crystal plasticity approach. Higher-order dissipative effects led to different results with dominant slip banding. Full article

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15 pages, 7375 KiB

Open AccessEditor’s ChoiceArticle

Mesomorphic and Thermal Behavior of Symmetric Bent-Core Liquid Crystal Compounds Derived from Resorcinol and Isophthalic Acid

by Catalina Ionica Ciobanu, Iulian Berladean, Elena-Luiza Epure, Aurel Simion, Gabriela Lisa, Yahia Boussoualem and Irina Carlescu

Crystals 2021, 11(10), 1215; https://doi.org/10.3390/cryst11101215 - 8 Oct 2021

Cited by 3 | Viewed by 2638

Abstract

Bent-core liquid crystals (BCLC) have been widely studied as a result of their unusual polar and chiral properties. Similar to calamitic and discotic molecules, BCLC molecules also exhibit nematic phases, besides other higher order mesophases. The aim of this work is to comparatively [...] Read more.

Bent-core liquid crystals (BCLC) have been widely studied as a result of their unusual polar and chiral properties. Similar to calamitic and discotic molecules, BCLC molecules also exhibit nematic phases, besides other higher order mesophases. The aim of this work is to comparatively analyze the mesomorphic behavior of some bent-core 1,3-disubstituted benzene core compounds derived from resorcinol and isophthalic acid. Thus, the two classes of compounds differ in the nature of the orientation of the ester bond between the benzene central core and the two branches attached to the core. The mesomorphic behavior was elucidated by polarized light optical microscopy and differential calorimetry. Given the relatively high isotropic points of the compounds, confirmation of the thermal stability in the domains manifesting liquid crystalline properties was performed by thermogravimetric studies. The theoretical explanation of the difference in mesomorphic behavior for the two classes was based on molecular modeling studies. Full article

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

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22 pages, 3834 KiB

Open AccessEditor’s ChoiceReview

On the Importance of σ–Hole Interactions in Crystal Structures

by Antonio Frontera and Antonio Bauzá

Crystals 2021, 11(10), 1205; https://doi.org/10.3390/cryst11101205 - 7 Oct 2021

Cited by 69 | Viewed by 6468

Abstract

Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems (aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF₄⁻, [...] Read more.

Elements from groups 14–18 and periods 3–6 commonly behave as Lewis acids, which are involved in directional noncovalent interactions (NCI) with electron-rich species (lone pair donors), π systems (aromatic rings, triple and double bonds) as well as nonnucleophilic anions (BF₄⁻, PF₆⁻, ClO₄⁻, etc.). Moreover, elements of groups 15 to 17 are also able to act as Lewis bases (from one to three available lone pairs, respectively), thus presenting a dual character. These emerging NCIs where the main group element behaves as Lewis base, belong to the σ–hole family of interactions. Particularly (i) tetrel bonding for elements belonging to group 14, (ii) pnictogen bonding for group 15, (iii) chalcogen bonding for group 16, (iv) halogen bonding for group 17, and (v) noble gas bondings for group 18. In general, σ–hole interactions exhibit different features when moving along the same group (offering larger and more positive σ–holes) or the same row (presenting a different number of available σ–holes and directionality) of the periodic table. This is illustrated in this review by using several examples retrieved from the Cambridge Structural Database (CSD), especially focused on σ–hole interactions, complemented with molecular electrostatic potential surfaces of model systems. Full article

(This article belongs to the Special Issue Advanced Research in Halogen Bonding)

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14 pages, 4212 KiB

Open AccessEditor’s ChoiceArticle

DFT Calculation, Hirshfeld Analysis and X-Ray Crystal Structure of Some Synthesized N-alkylated(S-alkylated)-[1,2,4]triazolo[1,5-a]quinazolines

by Hatem A. Abuelizz, Saied M. Soliman, Hazem A. Ghabbour, Mohamed Marzouk, Mohamed M. Abdellatif and Rashad Al-Salahi

Crystals 2021, 11(10), 1195; https://doi.org/10.3390/cryst11101195 - 30 Sep 2021

Cited by 2 | Viewed by 2451

Abstract

The present work aimed to synthesize 2-methylthio-triazoloquinazoline derivatives and study their X-ray, NMR, DFT and Hirshfeld characteristics. The cyclocondensation of dimethyl-N-cyanodithiocarbonate with 2-hydrazinobenzoic acid hydrochloride resulted in an intermediate, 2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-one (A), which upon treatment with phosphorus pentasulfide, [...] Read more.

The present work aimed to synthesize 2-methylthio-triazoloquinazoline derivatives and study their X-ray, NMR, DFT and Hirshfeld characteristics. The cyclocondensation of dimethyl-N-cyanodithiocarbonate with 2-hydrazinobenzoic acid hydrochloride resulted in an intermediate, 2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-one (A), which upon treatment with phosphorus pentasulfide, transformed into the 2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-thione (B). Reaction of 2-methylthio-triazoloquinazolines (A&B) with alkyl halides (allyl bromide and ethyl iodide) in basic medium afforded 4-allyl-2-methylthio-[1,2,4]triazolo[1,5-a]quinazolin-5-one (1; N-alkylated) and 5-ethylthio-2-methylthio-[1,2,4]triazolo[1,5-a]quinazoline (2; S-alkylated), respectively. Their molecular and supramolecular structures were presented. Unambiguously, the molecular structures of 1 and 2 were confirmed via NMR and single-crystal X-ray diffraction. The resulting findings confirmed the structures of 1 and 2 and determined their crystalized system (monoclinic system; P2₁/n space group). Hirshfeld analysis of 1 revealed the importance of the significantly short O···H (6.7%), S···S (1.2%) and C···C (2.8%); however, the short H···H (42.6%), S···H (16.3%) and C···C (4.3%) were showed in 2 by intermolecular interactions in the molecular packing. The 1,2,4-triazoloquinzolines (1&2) were anticipated to be relatively polar compounds with net dipole moments of 2.9284 and 4.2127 Debye, respectively. The molecular electrostatic potential, atomic charge distribution maps and reactivity descriptors for 1 and 2 were also determined. The calculated nuclear magnetic resonance spectra of the targets 1 and 2 were well correlated with the experimental data. Full article

(This article belongs to the Special Issue Crystal Engineering: From Molecules to Crystals to Functional Materials)

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13 pages, 6799 KiB

Open AccessEditor’s ChoiceArticle

Impact of a Partial Solid Solution and Water Molecules on the Formation of Fibrous Crystals and Fluid Inclusions

by Laureline Marc, Chrystal Lopes, Jean-Marie Schneider, Morgane Sanselme and Gérard Coquerel

Crystals 2021, 11(10), 1188; https://doi.org/10.3390/cryst11101188 - 29 Sep 2021

Cited by 7 | Viewed by 3176

Abstract

Resolution of (±)ibuprofen using S-α-Methylbenzylamine in pure ethanol leads to the enriched S-IBU/S-αMBA diastereomeric salt which crystallizes as very fine needles. In order to improve the filterability and processability of the solid phase, water can be added to the medium and lead to [...] Read more.

Resolution of (±)ibuprofen using S-α-Methylbenzylamine in pure ethanol leads to the enriched S-IBU/S-αMBA diastereomeric salt which crystallizes as very fine needles. In order to improve the filterability and processability of the solid phase, water can be added to the medium and lead to more equant particles that are still elongated. A high fraction of the resulting platelets display on both ends a fluid inclusion containing both liquid and a large bubble of gas. A detailed analysis of the particles reveals that they are not really single crystals but more an ordered association of fibers defined as fibrous crystal. A domain of partial solid solution is evidenced near the pure less soluble diastereomer and its impact on the formation of fibrous crystals is demonstrated. When pure S-IBU/S-αMBA diastereomeric salt is recrystallized in the same medium (e.g., ethanol–water) the crystallinity is improved, but fluid inclusions can still be observed. Full article

(This article belongs to the Special Issue Crystal Nucleation and Growth Kinetics)

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12 pages, 5203 KiB

Open AccessEditor’s ChoiceArticle

Ferroelectric Properties and Spectroscopic Characterization of Pb(Mg_1/3Nb_2/3)O₃-32PbTiO₃:Er³⁺/Sc³⁺ Crystal

by Jin Zhang, Zengzhe Xi, Xinzhe Wang, Hao Feng, Wei Long and Aiguo He

Crystals 2021, 11(10), 1155; https://doi.org/10.3390/cryst11101155 - 23 Sep 2021

Cited by 2 | Viewed by 2652

Abstract

An Er³⁺/Sc³⁺ co-doped 0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ ferroelectric single crystal was grown by high-temperature flux method. The remnant polarization Pr is 27.97 µC/cm² and the coercive field Ec is 8.26 kV/cm for [100] oriented crystal. [...] Read more.

An Er³⁺/Sc³⁺ co-doped 0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ ferroelectric single crystal was grown by high-temperature flux method. The remnant polarization Pr is 27.97 µC/cm² and the coercive field Ec is 8.26 kV/cm for [100] oriented crystal. Green (524 and 551 nm) and red (654 nm) emission bands are generated at the 980 nm excitation, which corresponds to the ²H_11/2→ ⁴I_15/2, ⁴S_3/2→ ⁴I_15/2 and ⁴F_9/2→ ⁴I_15/2 transitions of Er³⁺, respectively. Judd–Ofelt theory has been applied to predict the spectroscopic characteristics of the as-grown crystals. The obtained J–O intensity parameters Ω_t (t = 2, 4 and 6) are Ω₂ = 0.76 × 10⁻²⁰ cm², Ω₄ = 1.0 × 10⁻²⁰ cm², Ω₆ = 0.55 × 10⁻²⁰ cm². Spectroscopic characteristics, including optical transition probabilities, branching ratio, and radiative lifetime of Er³⁺ in the crystal, are determined. The calculated radiative lifetimes of ⁴I_13/2 and ⁴I_11/2 energy levels are 2.82 ms and 2.61 ms, respectively. These investigations provide possibilities for the crystal Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃:Er³⁺/Sc³⁺ to be a new type of multifunctional crystal integrating electricity-luminescence. Full article

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8 pages, 2171 KiB

Open AccessEditor’s ChoiceArticle

Multi-Component Crystals of 2,2′-Bipyridine with Aliphatic Dicarboxylic Acids: Melting Point-Structure Relations

by Vhukhudo Nethanani and Eustina Batisai

Crystals 2021, 11(10), 1151; https://doi.org/10.3390/cryst11101151 - 22 Sep 2021

Viewed by 2699

Abstract

The aim of the study was to investigate the relationship between the melting point and the supramolecular structure of three multi-component crystals of aliphatic dicarboxylic acids with 2,2′-bipyridine and to investigate the conformations of 2,2′-bipyridine in published multi-component crystals. The crystals were prepared [...] Read more.

The aim of the study was to investigate the relationship between the melting point and the supramolecular structure of three multi-component crystals of aliphatic dicarboxylic acids with 2,2′-bipyridine and to investigate the conformations of 2,2′-bipyridine in published multi-component crystals. The crystals were prepared using the solvent evaporation method and were characterized using single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), and differential scanning calorimetry (DSC). The crystal structures were further analyzed using CrystalExplorer, and the results were correlated with the melting points. The results of the conformation analysis of the reported multi-component crystals of 2,2′-bipyridine are also presented. Full article

(This article belongs to the Section Crystal Engineering)

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18 pages, 3542 KiB

Open AccessEditor’s ChoiceReview

Advances of Yb:CALGO Laser Crystals

by Hao Wang, Jing Pan, Yuan Meng, Qiang Liu and Yijie Shen

Crystals 2021, 11(9), 1131; https://doi.org/10.3390/cryst11091131 - 17 Sep 2021

Cited by 15 | Viewed by 7270

Abstract

Yb:CaGdAlO₄, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses [...] Read more.

Yb:CaGdAlO₄, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses with ever short durations. More specifically, its remarkable thermal-optic property and its high conversion efficiency allow high-power operation. Its high nonlinear coefficient facilitates study of optimized mode locking lasers. Besides, its ultrabroad and flat-top emission band benefits the generation of complex structured light with outstanding tunability. In this paper, we review the recent advances in the study of Yb:CALGO, covering its physical properties as well as its growing applications in various fields and prospect for future development. Full article

(This article belongs to the Special Issue Advanced Laser Technology and Applications)

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10 pages, 3112 KiB

Open AccessEditor’s ChoiceArticle

Bandgap and Carrier Dynamic Controls in CsPbBr₃ Nanocrystals Encapsulated in Polydimethylsiloxane

by Lianxing Liao, Kunhua Quan, Xiangshi Bin, Ruosheng Zeng and Tao Lin

Crystals 2021, 11(9), 1132; https://doi.org/10.3390/cryst11091132 - 17 Sep 2021

Cited by 5 | Viewed by 3890

Abstract

Bandgap tunability through ion substitution is a key feature of lead halide perovskite nanocrystals (LHP-NCs). However, the low stability and low luminescent performance of CsPbCl₃ hinder their full-color applications. In this work, quantum confinement effect (QCE) was utilized to control the bandgap [...] Read more.

Bandgap tunability through ion substitution is a key feature of lead halide perovskite nanocrystals (LHP-NCs). However, the low stability and low luminescent performance of CsPbCl₃ hinder their full-color applications. In this work, quantum confinement effect (QCE) was utilized to control the bandgap of CsPbBr₃ NCs instead of using unstable CsPbCl₃, which possess much higher emission efficiency in blue spectra region. Studies of microstructures, optical spectra and carrier dynamics revealed that tuning the reaction temperature was an effective way of controlling the NC sizes as well as QCE. Furthermore, the obtained CsPbBr₃ NCs were encapsulated in a PDMS matrix while maintaining their size distribution and quantum-confined optoelectronic properties. The encapsulated samples showed long-term air and water stability. These results provide valuable guidance for both applications of LHP-NCs and principal investigation related to the carrier transition in LHP-NCs. Full article

(This article belongs to the Section Materials for Energy Applications)

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12 pages, 5334 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Spatial Structures and Packaging of Phosphorybosil Pyrophosphate Synthetase 2 from Thermus thermophilus HB27 in Rhombohedral and Tetragonal Crystals

by Yulia Abramchik, Evgeniy Zayats, Maria Kostromina, Dmitry Lykoshin, Ilya Fateev, Irina Konstantinova, Nadezda Zhukhlistova, Vladimir Timofeev, Inna Kuranova and Roman Esipov

Crystals 2021, 11(9), 1128; https://doi.org/10.3390/cryst11091128 - 16 Sep 2021

Cited by 1 | Viewed by 2469

Abstract

We report the spatial structure of phosphoribosyl pyrophosphate synthetase 2 from the thermophilic bacterium Thermus thermophilus HB27 (TthPRPPS2) obtained at a 1.85 Å resolution using a diffraction set collected from rhombohedral crystals (space group R3₂-h), grown with lithium sulfate as [...] Read more.

We report the spatial structure of phosphoribosyl pyrophosphate synthetase 2 from the thermophilic bacterium Thermus thermophilus HB27 (TthPRPPS2) obtained at a 1.85 Å resolution using a diffraction set collected from rhombohedral crystals (space group R3₂-h), grown with lithium sulfate as a precipitant. This crystal structure was compared with the structure of TthPRPPS2, previously obtained at a 2.2 Å resolution using diffraction sets from the tetragonal crystals (space group P4₁2₁2), grown with ammonium sulfate as a precipitant. The comparison of these structures allows the study of the differences between protein molecules in both crystalline structures, as well as the packaging of enzyme molecules in crystals of both spatial groups. Our results may contribute to the research of the structural basis of catalytic activity and substrate specificity of this enzyme. Full article

(This article belongs to the Section Biomolecular Crystals)

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9 pages, 2340 KiB

Open AccessEditor’s ChoiceArticle

Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers

by Yi-Hong Shih, Xin-Yu Lin, Harry Miyosi Silalahi, Chia-Rong Lee and Chia-Yi Huang

Crystals 2021, 11(9), 1100; https://doi.org/10.3390/cryst11091100 - 10 Sep 2021

Cited by 10 | Viewed by 3528

Abstract

An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with [...] Read more.

An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metasurface under various polarized directions of the pump beam. Experimental results display that the resonance frequency of the metasurface in the cell increases with an increase in θ, and the cell has a frequency tuning region of 15 GHz. Simulated results reveal that the increase in the resonance frequency arises from the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The resonance frequency of the metasurface is shifted using the pump beam, so the metasurface-imbedded LC cell with the photoalignment layers is an optically tunable terahertz filter. The optically tunable terahertz filter is promising for applications in terahertz telecommunication, biosensing and terahertz imaging. Full article

(This article belongs to the Special Issue Liquid Crystal Optics for Applications)

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15 pages, 8295 KiB

Open AccessEditor’s ChoiceArticle

Thermal Deformations of Crystal Structures in the L-Aspartic Acid/L-Glutamic Acid System and DL-Aspartic Acid

by Roman Sadovnichii, Elena Kotelnikova and Heike Lorenz

Crystals 2021, 11(9), 1102; https://doi.org/10.3390/cryst11091102 - 10 Sep 2021

Cited by 3 | Viewed by 2952

Abstract

The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp_0.25,L-glu_0.75 solid solution. These amino acids were not found to undergo any [...] Read more.

The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp_0.25,L-glu_0.75 solid solution. These amino acids were not found to undergo any solid-phase (polymorph) transformations. When heated, they all experienced only thermal deformations. The corresponding parameters of the monoclinic cells of L-asp and DL-asp, and the orthorhombic cells of L-glu and L-asp_0.25,L-glu_0.75, were calculated for the entire range of studied temperatures (up to 220 °C). The data obtained were used to calculate the parameters of the thermal deformation tensors, and to plot the figures of their thermal expansion coefficients. A correlation between the maximum and minimum values of thermal expansion coefficients and the length, type, direction, and number of hydrogen bonds in the crystal structures of the investigated amino acids was established. The observed negative thermal expansion (contraction) of crystal structures of L-asp and DL-asp along the ac plane can be explained as a result of shear deformations occurring in monoclinic crystals with a non-fixed angle β. The studies were related to the presence of amino acids in various natural and technological processes occurring at different temperatures. Full article

(This article belongs to the Special Issue Recent Progress in Industrial Crystallization)

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12 pages, 596 KiB

Open AccessEditor’s ChoiceArticle

The Refraction Indices and Brewster Law in Stressed Isotropic Materials and Cubic Crystals

by Daniele Rinaldi, Pier Paolo Natali, Luigi Montalto and Fabrizio Davì

Crystals 2021, 11(9), 1104; https://doi.org/10.3390/cryst11091104 - 10 Sep 2021

Cited by 2 | Viewed by 2331

Abstract

We study the elasto-optic behavior of stressed cubic crystals (all classes) and isotropic materials (like e.g., glasses). We obtain the explicit dependence of the refraction indices on the stress (either applied or residual), as well as a mild generalization of the Brewster law [...] Read more.

We study the elasto-optic behavior of stressed cubic crystals (all classes) and isotropic materials (like e.g., glasses). We obtain the explicit dependence of the refraction indices on the stress (either applied or residual), as well as a mild generalization of the Brewster law for cubic crystals. We show also that the optic indicatrix and the stress ellipsoid are coaxial only in the isotropic case. This theory allows the improvement of the measurement techniques, as photoelasticity, on cubic crystals and optically isotropic materials. Full article

(This article belongs to the Special Issue Photoelasticity in Optical Media from Crystals to Amorphous Materials)

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13 pages, 2827 KiB

Open AccessEditor’s ChoiceArticle

Remarkable Increase of Fluorescence Quantum Efficiency by Cyano Substitution on an ESIPT Molecule 2-(2-Hydroxyphenyl)benzothiazole: A Highly Photoluminescent Liquid Crystal Dopant

by Tsuneaki Sakurai, Masaya Kobayashi, Hiroyuki Yoshida and Masaki Shimizu

Crystals 2021, 11(9), 1105; https://doi.org/10.3390/cryst11091105 - 10 Sep 2021

Cited by 18 | Viewed by 4729

Abstract

Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (Φ_FL) in [...] Read more.

Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (Φ_FL) in the solution or viscous media, due to their structural relaxations in the excited state to reach the S₀/S₁ conical intersection, shackle further applications of ESIPT-active luminophores. Here we report that the introduction of a cyano group (-CN) into the phenyl group of 2-(2-hydroxyphenyl)benzothiazole (HBT), a representative ESIPT compound, remarkably increase its fluorescence quantum yield (Φ_FL) from 0.01 (without -CN) to 0.49 (with -CN) in CH₂Cl₂, without disturbing its high Φ_FL (=0.52) in the solid state. The large increase of the solution-state Φ_FL of the cyano-substituted HBT (CN-HBT) is remarkable, comparing with our previously reported Φ_FL values of 0.05 (with 4-pentylphenyl), 0.07 (with 1-hexynyl), and 0.15 (with 4-pentylphenylethynyl). Of interest, the newly-synthesized compound, CN-HBT, is miscible in a conventional room-temperature nematic liquid crystal (LC), 4-pentyl-4′-cyano biphenyl (5CB), up to 1 wt% (~1 mol%), and exhibits a large Φ_FL of 0.57 in the viscous LC medium. A similar Φ_FL value of Φ_FL = 0.53 was also recorded in another room-temperature LC, trans-4-(4-pentylcyclohexyl)benzonitrile (PCH5), with a doping ratio of 0.5 wt% (~0.5 mol%). These 5CB/CN-HBT and PCH5/CN-HBT mixtures serve as light-emitting room-temperature LCs, and show anisotropic fluorescence with the dichroic ratio of 3.1 upon polarized excitation, as well as electric field response of luminescence intensity changes. Full article

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

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14 pages, 921 KiB

Open AccessEditor’s ChoiceArticle

Photoelastic Properties of Trigonal Crystals

by Bohdan Mytsyk, Nataliya Demyanyshyn, Anatoliy Andrushchak and Oleh Buryy

Crystals 2021, 11(9), 1095; https://doi.org/10.3390/cryst11091095 - 8 Sep 2021

Cited by 8 | Viewed by 3244

Abstract

All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) π_im and some sums of π_im based on experimental [...] Read more.

All possible experimental geometries of the piezo-optic effect in crystals of trigonal symmetry are studied in detail through the interferometric technique, and the corresponding expressions for the calculation of piezo-optic coefficients (POCs) π_im and some sums of π_im based on experimental data obtained from the samples of direct and X/45°-cuts are given. The reliability of the values of POCs is proven by the convergence of π_im obtained from different experimental geometries as well as by the convergence of some sums of POCs. Because both the signs and the absolute values of POCs π₁₄ and π₄₁ are defined by the choice of the right crystal-physics coordinate system, we here use the system whereby the condition S₁₄ > 0 is fulfilled (S₁₄ is an elastic compliance coefficient). The absolute value and the sign of S₁₄ are determined by piezo-optic interferometric method from two experimental geometries. The errors of POCs are calculated as mean square values of the errors of the half-wave stresses and the elastic term. All components of the matrix of elasto-optic coefficients p_in are calculated based on POCs and elastic stiffness coefficients. The technique is tested on LiTaO₃ crystal. The obtained results are compared with the corresponding data for trigonal LiNbO₃ and Ca₃TaGa₃Si₂O₁₄ crystals. Full article

(This article belongs to the Special Issue Photoelasticity in Optical Media from Crystals to Amorphous Materials)

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19 pages, 3321 KiB

Open AccessEditor’s ChoiceArticle

Synthesis, Crystal Structure, Inhibitory Activity and Molecular Docking of Coumarins/Sulfonamides Containing Triazolyl Pyridine Moiety as Potent Selective Carbonic Anhydrase IX and XII Inhibitors

by Yassine Aimene, Romain Eychenne, Frédéric Rodriguez, Sonia Mallet-Ladeira, Nathalie Saffon-Merceron, Jean-Yves Winum, Alessio Nocentini, Claudiu T. Supuran, Eric Benoist and Achour Seridi

Crystals 2021, 11(9), 1076; https://doi.org/10.3390/cryst11091076 - 6 Sep 2021

Cited by 15 | Viewed by 4593

Abstract

In this work, two classes of Carbonic Anhydrase (CA) inhibitors, sulfonamide and coumarin derivatives linked to pyta moiety (2a-b) and their corresponding rhenium complexes (3a-b), were designed. These compounds were synthesized and fully characterized by classical analytical methods and [...] Read more.

In this work, two classes of Carbonic Anhydrase (CA) inhibitors, sulfonamide and coumarin derivatives linked to pyta moiety (2a-b) and their corresponding rhenium complexes (3a-b), were designed. These compounds were synthesized and fully characterized by classical analytical methods and X-ray diffraction. All the synthesized compounds were evaluated for their inhibitory activity against the hCA isoforms I, II, IX and XII. They exhibited high inhibitory activities in the range of nanomolar for both hCA IX and hCA XII isoforms. The sulfonamide compound 2a showed the strongest inhibition against the tumour-associated hCA IX isoform with a Ki of 11.7 nM. The tumour-associated isoforms hCA IX and hCA XII were selectively inhibited by all the coumarin derivatives, with inhibition constants ranging from 12.7 nM (2b) to 44.5 nM (3b), while the hCA I and II isoforms were slightly inhibited (in the micromolar range), as expected. In terms of selectivity, compared to previously published rhenium complex-based CA inhibitors, complex 3b showed one of the highest selectivities against hCA IX and hCA XII compared to the off-target isoforms hCA I and hCA II, making it a potential anti-cancer drug candidate. Molecular docking calculations were performed to investigate the inhibition profiles of the investigated compounds at the tumour-associated hCA IX active site and to rationalize our results. Full article

(This article belongs to the Special Issue Discovery, Modeling, Synthesis and Performance Evaluation of Enzyme Inhibitors)

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12 pages, 2687 KiB

Open AccessEditor’s ChoiceArticle

Scanning Electron Microscopy Investigation of Surface Acoustic Wave Propagation in a 41° YX-Cut of a LiNbO₃ Crystal/Si Layered Structure

by Dmitry Roshchupkin, Evgenii Emelin, Olga Plotitcina, Anatoly Mololkin and Oleg Telminov

Crystals 2021, 11(9), 1082; https://doi.org/10.3390/cryst11091082 - 6 Sep 2021

Cited by 6 | Viewed by 3044

Abstract

The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO₃ crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration [...] Read more.

The propagation process of the surface acoustic waves (SAW) and the pseudo-surface acoustic waves (PSAW) in a bonded layered structure of a 41° YX-cut of a LiNbO₃ crystal/Si(100) crystal was investigated. The scanning electron microscopy (SEM) method,in the low-energy secondary electrons registration mode, made it possible to visualize the SAW and PSAW in the LiNbO₃/Si layered structure. The process of the SAW and PSAW propagation in a LiNbO₃/Si layered structure and in a bulk 41° YX-cut of a LiNbO₃ crystal were compared. It was demonstrated that the SAW velocities in the layered LiNbO₃/Si structure exceed the typical SAW velocities for LiNbO₃ and Si single crystals. In the layered structure, the SAW and PSAW velocities were 4062 m/s, 4731 m/s, and 5871 m/s. It was also demonstrated that the PSAW velocities are the same in the LiNbO₃/Si layered structure and in the bulk 41° YX-cut of a LiNbO₃ crystal. Full article

(This article belongs to the Special Issue Ferroelectric and Piezoelectric Crystals)

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12 pages, 1855 KiB

Open AccessEditor’s ChoiceArticle

Growth of Acetaminophen Polymorphic Crystals and Solution-Mediated Phase Transition from Trihydrate to Form II in Agarose Gel

by Akari Nishigaki, Mihoko Maruyama, Shun-ichi Tanaka, Hiroshi Y. Yoshikawa, Masayuki Imanishi, Masashi Yoshimura, Yusuke Mori and Kazufumi Takano

Crystals 2021, 11(9), 1069; https://doi.org/10.3390/cryst11091069 - 5 Sep 2021

Cited by 2 | Viewed by 3473

Abstract

The growth of acetaminophen polymorphic crystals and the solution-mediated phase transition from trihydrate to form II in agarose gel were investigated. The form II crystals grown in gels, presumably because of the agarose content, dissolved less rapidly at high temperatures and were more [...] Read more.

The growth of acetaminophen polymorphic crystals and the solution-mediated phase transition from trihydrate to form II in agarose gel were investigated. The form II crystals grown in gels, presumably because of the agarose content, dissolved less rapidly at high temperatures and were more stable than in water. The trihydrate crystals in the gel were also expected to be stabilized by containing agarose, but in fact the fine morphology resulted in reduced stability. The solution-mediated phase transition from trihydrate to form II via form II seeding took longer in the gel because the gel slowed down the dissolution of the trihydrate by hindering the dispersion of the form II seeds and delayed the growth of form II by reducing the diffusion rate of the molecules dissolved from the trihydrate. Delays in solution-mediated phase transition and changes in stability for crystals grown in gels indicate the effectiveness of gels in controlling polymorphisms in pharmaceutical compounds. Full article

(This article belongs to the Special Issue Crystallization Processes: Food and Pharmaceutical Crystals)

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12 pages, 4047 KiB

Open AccessEditor’s ChoiceArticle

Control of Crystallographic Texture and Mechanical Properties of Hastelloy-X via Laser Powder Bed Fusion

by Shinya Hibino, Tsubasa Todo, Takuya Ishimoto, Ozkan Gokcekaya, Yuichiro Koizumi, Kenichiroh Igashira and Takayoshi Nakano

Crystals 2021, 11(9), 1064; https://doi.org/10.3390/cryst11091064 - 3 Sep 2021

Cited by 37 | Viewed by 4931

Abstract

The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like [...] Read more.

The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like microstructure with <100>//build direction (BD) (<100>-SCM), single crystalline-like microstructure with <110>//BD (<110>-SCM), crystallographic lamellar microstructure (CLM), or polycrystalline microstructure (PCM). These four crystallographic textures were realized in Hastelloy-X for the first time here to the best of our knowledge. The mechanical properties of the samples varied depending on their texture. The tensile properties were affected not only by the Schmid factor but also by the grain size and the presence of lamellar boundaries (grain boundaries). The lamellar boundaries at the interface between the <110>//BD oriented main layers and the <100>//BD-oriented sub-layers of CLM contributed to the resistance to slip transmission and the increased proof stress. It was possible to control a wide range of crystallographic microstructures via the LPBF process parameters, which determines the melt pool morphology and solidification behavior. Full article

(This article belongs to the Special Issue Additive Manufacturing: Materials, Processing, Characterization and Applications)

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10 pages, 2592 KiB

Open AccessEditor’s ChoiceReview

Optically Rewritable Liquid Crystal Displays: Characteristics and Performance

by Vladimir G. Chigrinov, Aleksey A. Kudreyko and Fedor V. Podgornov

Crystals 2021, 11(9), 1053; https://doi.org/10.3390/cryst11091053 - 1 Sep 2021

Cited by 6 | Viewed by 3055

Abstract

Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing [...] Read more.

Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing studies do not include sufficient analysis on how to achieve acceptable reflective characteristics within short exposure time. In order to achieve this goal, we have applied the rotational diffusion model. We find that the parameters of the diffusion model can be adjusted to get acceptable light-reflecting characteristics within 10 s of exposure. In comparison with the long-time exposure, the reflectance coefficient reduces by 24%. The route to material improvements for optimized e-paper device is discussed. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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7 pages, 676 KiB

Open AccessEditor’s ChoiceCommunication

Using DFT to Calculate the Parameters of the Crystal Field in Mn²⁺ Doped Hydroxyapatite Crystals

by Daria Vladimirovna Shurtakova, Peter Olegovich Grishin, Marat Revgerovich Gafurov and Georgy Vladimirovich Mamin

Crystals 2021, 11(9), 1050; https://doi.org/10.3390/cryst11091050 - 31 Aug 2021

Cited by 10 | Viewed by 3773

Abstract

Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxyapatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized [...] Read more.

Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxyapatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized Mn-HAp powders Ca₉.₉₉₅Mn₀.₀₀₅(PO₄)₆(OH)₂. It is found that in the investigated species, the manganese is redistributed between both calcium sites with prevalence in Ca (I). Agreement between the calculated and experimental data proves that crystal field parameters in HAp can be calculated in the classical DFT model using the distributed electron density. Full article

(This article belongs to the Special Issue Hydroxyapatite Base Nanocomposites (Volume II))

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16 pages, 2644 KiB

Open AccessEditor’s ChoiceArticle

Crystal-Site-Based Artificial Neural Networks for Material Classification

by Juan I. Gómez-Peralta, Nidia G. García-Peña and Xim Bokhimi

Crystals 2021, 11(9), 1039; https://doi.org/10.3390/cryst11091039 - 29 Aug 2021

Cited by 5 | Viewed by 5602

Abstract

In materials science, crystal structures are the cornerstone in the structure–property paradigm. The description of crystal compounds may be ascribed to the number of different atomic chemical environments, which are related to the Wyckoff sites. Hence, a set of features related to the [...] Read more.

In materials science, crystal structures are the cornerstone in the structure–property paradigm. The description of crystal compounds may be ascribed to the number of different atomic chemical environments, which are related to the Wyckoff sites. Hence, a set of features related to the different atomic environments in a crystal compound can be constructed as input data for artificial neural networks (ANNs). In this article, we show the performance of a series of ANNs developed using crystal-site-based features. These ANNs were developed to classify compounds into halite, garnet, fluorite, hexagonal perovskite, ilmenite, layered perovskite, -o-tp- perovskite, perovskite, and spinel structures. Using crystal-site-based features, the ANNs were able to classify the crystal compounds with a 93.72% average precision. Furthermore, the ANNs were able to retrieve missing compounds with one of these archetypical structure types from a database. Finally, we showed that the developed ANNs were also suitable for a multitask learning paradigm, since the extracted information in the hidden layers linearly correlated with lattice parameters of the crystal structures. Full article

(This article belongs to the Special Issue Applications of Machine Learning to the Study of Crystalline Materials)

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25 pages, 8705 KiB

Open AccessEditor’s ChoiceArticle

Crystal Structure, Vibrational, Spectroscopic and Thermochemical Properties of Double Sulfate Crystalline Hydrate [CsEu(H₂O)₃(SO₄)₂]·H₂O and Its Thermal Dehydration Product CsEu(SO₄)₂

by Yuriy G. Denisenko, Maxim S. Molokeev, Aleksandr S. Oreshonkov, Alexander S. Krylov, Aleksandr S. Aleksandrovsky, Nikita O. Azarapin, Oleg V. Andreev, Illaria A. Razumkova and Victor V. Atuchin

Crystals 2021, 11(9), 1027; https://doi.org/10.3390/cryst11091027 - 26 Aug 2021

Cited by 73 | Viewed by 5052

Abstract

Crystalline hydrate of double cesium europium sulfate [CsEu(H₂O)₃(SO₄)₂]·H₂O was synthesized by the crystallization from an aqueous solution containing equimolar amounts of 1Cs⁺:1Eu³⁺:2SO₄²⁻ ions. Anhydrous salt CsEu(SO₄ [...] Read more.

Crystalline hydrate of double cesium europium sulfate [CsEu(H₂O)₃(SO₄)₂]·H₂O was synthesized by the crystallization from an aqueous solution containing equimolar amounts of 1Cs⁺:1Eu³⁺:2SO₄²⁻ ions. Anhydrous salt CsEu(SO₄)₂ was formed as a result of the thermal dehydration of the crystallohydrate. The unusual effects observed during the thermal dehydration were attributed to the specific coordination of water molecules in the [CsEu(H₂O)₃(SO₄)₂]·H₂O structure. The crystal structure of [CsEu(H₂O)₃(SO₄)₂]·H₂O was determined by a single crystal X-ray diffraction analysis, and the crystal structure of CsEu(SO₄)₂ was obtained by the Rietveld method. [CsEu(H₂O)₃(SO₄)₂]·H₂O crystallizes in the monoclinic system, space group P2₁/c (a = 6.5574(1) Å, b = 19.0733(3) Å, c = 8.8364(2) Å, β = 93.931(1)°, V = 1102.58(3) Å3). The anhydrous sulfate CsEu(SO₄)₂ formed as a result of the thermal destruction crystallizes in the monoclinic system, space group C2/c (a = 14.327(1) Å, b = 5.3838(4) Å, c = 9.5104(6) Å, β = 101.979(3) °, V = 717.58(9) Å3). The vibration properties of the compounds are fully consistent with the structural models and are mainly determined by the deformation of non-rigid structural elements, such as H₂O and SO₄²⁻. As shown by the diffused reflection spectra measurements and DFT calculations, the structural transformation from [CsEu(H₂O)₃(SO₄)₂]·H₂O to CsEu(SO₄)₂ induced a significant band gap reduction. A noticeable difference of the luminescence spectra between cesium europium sulfate and cesium europium sulfate hydrate is detected and explained by the variation of the extent of local symmetry violation at the crystallographic sites occupied by Eu³⁺ ions, namely, by the increase in inversion asymmetry in [CsEu(H2O)₃(SO₄)₂]·H₂O and the increase in mirror asymmetry in CsEu(SO₄)₂. The chemical shift of the ⁵D₀ energy level in cesium europium sulfate hydrate, with respect to cesium europium sulfate, is associated with the presence of H₂O molecules in the vicinity of Eu³⁺ ion. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals Volume II)

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12 pages, 895 KiB

Open AccessEditor’s ChoiceArticle

Tunable Bandgaps in Phononic Crystal Microbeams Based on Microstructure, Piezo and Temperature Effects

by Jun Hong, Zhuangzhuang He, Gongye Zhang and Changwen Mi

Crystals 2021, 11(9), 1029; https://doi.org/10.3390/cryst11091029 - 26 Aug 2021

Cited by 15 | Viewed by 2673

Abstract

A new model of non-classical phononic crystal (PC) microbeam for the elastic wave bandgap generation is provided, incorporating microstructure, piezomagnetism, piezoelectricity and temperature effects. The wave equation of a general magneto–electro–elastic (MEE) phononic crystal microbeam is derived, which recovers piezoelectric- and piezomagnetic-based counterparts [...] Read more.

A new model of non-classical phononic crystal (PC) microbeam for the elastic wave bandgap generation is provided, incorporating microstructure, piezomagnetism, piezoelectricity and temperature effects. The wave equation of a general magneto–electro–elastic (MEE) phononic crystal microbeam is derived, which recovers piezoelectric- and piezomagnetic-based counterparts as special cases. The piezomagnetic and piezoelectric materials are periodically combined to construct the PC microbeam and corresponding bandgaps are obtained by using the plane wave expansion (PWE) method. The effects of the piezomagnetism, piezoelectricity, microstructure, geometrical parameters and applied multi-fields (e.g., external electric potential, external magnetic potential, temperature change) on the bandgaps are discussed. The numerical results reveal that the bandgap frequency is raised with the presence of piezo and microstructure effects. In addition, the geometry parameters play an important role on the bandgap. Furthermore, large bandgaps can be realized by adjusting the external electric and magnetic potentials at micron scale, and lower bandgap frequency can be realized through the temperature rise at all length scales. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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16 pages, 8742 KiB

Open AccessEditor’s ChoiceReview

A Review of Two-Dimensional Liquid Crystal Polarization Gratings

by Kai Zuo, Yue Shi and Dan Luo

Crystals 2021, 11(9), 1015; https://doi.org/10.3390/cryst11091015 - 25 Aug 2021

Cited by 11 | Viewed by 5199

Abstract

In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal [...] Read more.

In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal manipulation stimulates the development of multibeam optical devices. Therefore, the development of two-dimensional (2D) PGs is in demand. This review summarizes the research progress of 2D PGs. Different designs and fabrication methods are summarized, including assembling two 1D polarization patterns, a 2D holographic lithography by polarization interference and a micro-pixelated electric field stimulated 2D liquid crystal (LC) structure. Both experiments and analyses are included. The design strategy, diffraction property, merits and demerits are discussed and summarized for the different methods. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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11 pages, 4302 KiB

Open AccessEditor’s ChoiceArticle

Crystalline Silicon Spalling as a Direct Application of Temperature Effect on Semiconductors’ Indentation

by Maha M. Khayyat

Crystals 2021, 11(9), 1020; https://doi.org/10.3390/cryst11091020 - 25 Aug 2021

Cited by 1 | Viewed by 2839

Abstract

Kerf-less removal of surface layers of photovoltaic materials including silicon is an emerging technology by controlled spalling technology. The method is extremely simple, versatile, and applicable to a wide range of substrates. Controlled spalling technology requires a stressor layer, such as Ni, to [...] Read more.

Kerf-less removal of surface layers of photovoltaic materials including silicon is an emerging technology by controlled spalling technology. The method is extremely simple, versatile, and applicable to a wide range of substrates. Controlled spalling technology requires a stressor layer, such as Ni, to be deposited on the surface of a brittle material; then, the controlled removal of a continuous surface layer can be performed at a predetermined depth by manipulating the thickness and stress of the Ni layer, introducing a crack near the edge of the substrate, and mechanically guiding the crack as a single fracture front across the surface. However, spalling Si(100) at 300 K (room temperature RT) introduced many cracks and rough regions within the spalled layer. These mechanical issues make it difficult to process these layers of Si(100) for PV, and in other advanced applications, Si does not undergo phase transformations at 77 K (Liquid Nitrogen Temperature, LNT); based on this fact, spalling of Si(100) has been carried out. Spalling of Si(100) at LNT improved material quality for further designed applications. Mechanical flexibility is achieved by employing controlled spalling technology, enabling the large-area transfer of ultrathin body silicon devices to a plastic substrate at room temperature. Full article

(This article belongs to the Special Issue Fabrication of Carbon and Related Materials/Metal Hybrids and Composites)

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12 pages, 3580 KiB

Open AccessEditor’s ChoiceArticle

Crystal Plasticity with Micromorphic Regularization in Assessing Scale Dependent Deformation of Polycrystalline Doped Copper Alloys

by Matti Lindroos, Tom Andersson, Jarkko Metsäjoki and Anssi Laukkanen

Crystals 2021, 11(8), 994; https://doi.org/10.3390/cryst11080994 - 21 Aug 2021

Cited by 2 | Viewed by 2580

Abstract

It is planned that doped copper overpacks will be utilized in the spent nuclear fuel repositories in Finland and in Sweden. The assessment of long-term integrity of the material is a matter of importance. Grain structure variations, segregation and any possible manufacturing defects [...] Read more.

It is planned that doped copper overpacks will be utilized in the spent nuclear fuel repositories in Finland and in Sweden. The assessment of long-term integrity of the material is a matter of importance. Grain structure variations, segregation and any possible manufacturing defects in microstructure are relevant in terms of susceptibility to creep and damage from the loading evolution imposed by its operating environment. This work focuses on studying the microstructure level length-scale dependent deformation behavior of the material, of particular significance with respect to accumulation of plasticity over the extensive operational period of the overpacks. The reduced micromorphic crystal plasticity model, which is similar to strain gradient models, is used in this investigation. Firstly, the model’s size dependent plasticity effects are evaluated. Secondly, different microstructural aggregates presenting overpack sections are analyzed. Grain size dependent hardening responses, i.e., Hall-Petch like behavior, can be achieved with the enhanced hardening associated with the micromorphic model at polycrystalline level. It was found that the nominally large grain size in the base material of the overpack shows lower strain hardening potential than the fine grained region of the welded microstructure with stronger strain gradient related hardening effects. Size dependent regularization of strain localization networks is indicated as a desired characteristic of the model. The findings can be utilized to provide an improved basis for modeling the viscoplastic deformation behavior of the studied copper alloy and to assess the microstructural origins of any integrity concerns explicitly by way of full field modeling. Full article

(This article belongs to the Special Issue Micromechanical Modelling and Its Applications to Polycrystals)

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13 pages, 17495 KiB

Open AccessEditor’s ChoiceArticle

Growth of SrB₄O₇ Crystal Fibers along the c-Axis by Micro-Pulling-Down Method

by Ryouta Ishibashi, Harutoshi Asakawa and Ryuichi Komatsu

Crystals 2021, 11(8), 987; https://doi.org/10.3390/cryst11080987 - 20 Aug 2021

Cited by 1 | Viewed by 3301

Abstract

SrB₄O₇ (SBO) receives much attention as solid-state ultraviolet lasers for micro-machining, photochemical synthesis, and laser spectroscopy. For the application of SBO, the SBO crystals require the control of twinning to amplify the conversion light. We also expected that the inhibitation [...] Read more.

SrB₄O₇ (SBO) receives much attention as solid-state ultraviolet lasers for micro-machining, photochemical synthesis, and laser spectroscopy. For the application of SBO, the SBO crystals require the control of twinning to amplify the conversion light. We also expected that the inhibitation of the SrB₂O₄ appearance was essential. Here, we show the growth of SBO crystals along the c-axis through the micro-pulling-down method while alternating the application of electric fields (E). Without the application, single crystals were grown. At E ≧ 400 V/cm no needle domains of SrB₂O₄ inside SBO crystals existed; however, composition planes were formed and twin boundaries did not appear. In contrast, the inversion of surface morphology emerged, and the convex size was especially large at 1000 V/cm. These results demonstrate that convection is generated perpendicular to the growth front by alternating the application of electric fields. This surface morphological change contradicts the conventional concept of growth through the micro-pulling-down method. The distance from seed crystals vs. grain density plot also showed that the density did not decrease with a sufficient slope. Consequently, we concluded that the selection of the c-axis as growth faces is not fruitful to fabricate twins, and the selection of the growth condition, under which geometrical selection strongly affects, is the key. Full article

(This article belongs to the Special Issue New Trends in Growth Technique of Micro-Pulling-Down Method)

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19 pages, 21632 KiB

Open AccessEditor’s ChoiceArticle

Influences of Chemical Functionalities on Crystal Structures and Electrochemical Properties of Dihydro-benzoxazine Dimer Derivatives

by Natapol Suetrong, Kantapat Chansaenpak, Sarawoot Impeng, Piyanut Pinyou, Vincent Blay, Rubén Blay-Roger, Sireerat Lisnund, Pongsakorn Kanjanaboos, Yuranan Hanlumyuang, Suttipong Wannapaiboon and Worawat Wattanathana

Crystals 2021, 11(8), 979; https://doi.org/10.3390/cryst11080979 - 18 Aug 2021

Cited by 6 | Viewed by 4823

Abstract

Dihydro-1,3,2H-benzoxazine dimer derivatives or dihydro-benzoxazine dimers are a class of compounds typically prepared by ring-opening reactions between dihydro-benzoxazines and phenols. Dihydro-benzoxazine dimers act as chelating agents for several transition and rare-earth cations. To better understand the chelating properties, it is necessary [...] Read more.

Dihydro-1,3,2H-benzoxazine dimer derivatives or dihydro-benzoxazine dimers are a class of compounds typically prepared by ring-opening reactions between dihydro-benzoxazines and phenols. Dihydro-benzoxazine dimers act as chelating agents for several transition and rare-earth cations. To better understand the chelating properties, it is necessary to examine their structural features and electrochemical characteristics thoroughly. However, the electrochemical properties of dihydro-benzoxazine dimers have not been tremendously examined. Herein, eight derivatives of dihydro-benzoxazine dimers possessing different substituents on the benzene ring and the tertiary-amine nitrogen were synthesized as model compounds to investigate their influences on crystal structures and electrochemical properties. The crystal structure of the dihydro-benzoxazine dimer, namely 2,2′-(cyclohexylazanediyl)bis(methylene)bis(4-methoxyphenol) (7), is identified for the first time and further used to compare with the crystal structures of other derivatives reported previously. For all the derivatives, intermolecular O–H⋅⋅⋅O hydrogen bonds are the significant interactions to hold the crystal packing of (7) and also the other derivatives. Hirshfeld surface analyses confirm the presence of intermolecular O–H⋅⋅⋅O hydrogen bonds. Redox behavior of the eight dihydro-benzoxazine dimers was studied by cyclic voltammetry. An oxidation peak observed at 0.25–0.47 V corresponds to the oxidation of the phenolic –OH group to the phenoxonium intermediate. The shift in the electrochemical peak positions is due to the different abilities of the substituents to stabilize the phenoxonium cation intermediate. The stabilizing power is ranged in the following order: methoxy > dimethyl > ethyl ≈ methyl, and N-cyclohexyl > N-methyl. Thus, the derivative (7), which contains both the methoxy and N-cyclohexyl groups, has the lowest oxidation potential. Our work elucidates the effect of the substituents on the crystal structures and electrochemical properties of the dihydro-benzoxazine dimers. Full article

(This article belongs to the Section Organic Crystalline Materials)

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14 pages, 3732 KiB

Open AccessEditor’s ChoiceArticle

Mesomorphic Behaviour and DFT Insight of Arylidene Schiff Base Liquid Crystals and Their Pyridine Impact Investigation

by Mohamed A. Zakaria, Mohammed Alazmi, Kanubhai D. Katariya, Yeldez El Kilany, El Sayed H. El Ashry, Mariusz Jaremko, Mohamed Hagar and Sayed Z. Mohammady

Crystals 2021, 11(8), 978; https://doi.org/10.3390/cryst11080978 - 18 Aug 2021

Cited by 15 | Viewed by 3318

Abstract

A new series of Schiff base liquid crystal have been prepared and studied. Schiff bases of p-alkyl aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were prepared. The terminal alkyl groups substituting aniline are of varied chain length, namely C8, C12 and C14. The structures of [...] Read more.

A new series of Schiff base liquid crystal have been prepared and studied. Schiff bases of p-alkyl aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were prepared. The terminal alkyl groups substituting aniline are of varied chain length, namely C8, C12 and C14. The structures of the compounds were elucidated by 1H NMR and 13C NMR. The mesomorphic thermal and optical characteristics of the samples were determined via differential thermal analysis (DSC) and polarization optical microscopy (POM). All compounds exhibit enantiotropic dimorphic mesophase behaviour, referred to as smectic X1 (SmX1) and smectic X2 (Sm A). Experimental results obtained for the mesophases were correlated with density functional theory (DFT) theoretical calculations. The results of the new series are further compared to two series of compounds bearing pyridine (two ring Schiff bases) and biphenyl, respectively, in their mesogens. The series of compounds of one pyridine ring are generally not mesomorphic. The results indicate that the alkyl chain length has a strong impact on the mesomorphic characteristics and thermal stabilities of the different mesophases. As a trend, the temperature ranges of both of smectic mesophases of all compounds are higher in new compounds bearing the 4-phenyl pyridine moiety. In addition, the total mesophase range is generally higher in the new compounds when compared to their biphenyl analogues. Finally, theoretical DFT calculations were performed to illustrate the experimental finding of the mesomorphic behaviour in terms of the molecular geometry and aromaticity, π–π stacking and LOL-π. Full article

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

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14 pages, 4924 KiB

Open AccessEditor’s ChoiceArticle

Transfer of a Rational Crystal Contact Engineering Strategy between Diverse Alcohol Dehydrogenases

by Brigitte Walla, Daniel Bischoff, Robert Janowski, Nikolas von den Eichen, Dierk Niessing and Dirk Weuster-Botz

Crystals 2021, 11(8), 975; https://doi.org/10.3390/cryst11080975 - 17 Aug 2021

Cited by 7 | Viewed by 4331

Abstract

Protein crystallization can serve as a purification step in biotechnological processes but is often limited by the non-crystallizability of proteins. Enabling or improving crystallization is mostly achieved by high-throughput screening of crystallization conditions and, more recently, by rational crystal contact engineering. Two selected [...] Read more.

Protein crystallization can serve as a purification step in biotechnological processes but is often limited by the non-crystallizability of proteins. Enabling or improving crystallization is mostly achieved by high-throughput screening of crystallization conditions and, more recently, by rational crystal contact engineering. Two selected rational crystal contact mutations, Q126K and T102E, were transferred from the alcohol dehydrogenases of Lactobacillus brevis (LbADH) to Lactobacillus kefir (LkADH). Proteins were expressed in E. coli and batch protein crystallization was performed in stirred crystallizers. Highly similar crystal packing of LkADH wild type compared to LbADH, which is necessary for the transfer of crystal contact engineering strategies, was achieved by aligning purification tag and crystallization conditions, as shown by X-ray diffraction. After comparing the crystal sizes after crystallization of LkADH mutants with the wild type, the mean protein crystal size of LkADH mutants was reduced by 40–70% in length with a concomitant increase in the total amount of crystals (higher number of nucleation events). Applying this measure to the LkADH variants studied results in an order of crystallizability T102E > Q126K > LkADH wild type, which corresponds to the results with LbADH mutants and shows, for the first time, the successful transfer of crystal contact engineering strategies. Full article

(This article belongs to the Special Issue Bulk Protein Crystallization)

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16 pages, 876 KiB

Open AccessEditor’s ChoiceReview

Engineering Crystal Packing in RNA Structures I: Past and Future Strategies for Engineering RNA Packing in Crystals

by Narsimha Pujari, Stephanie L. Saundh, Francis A. Acquah, Blaine H. M. Mooers, Adrian R. Ferré-D’Amaré and Adelaine Kwun-Wai Leung

Crystals 2021, 11(8), 952; https://doi.org/10.3390/cryst11080952 - 15 Aug 2021

Cited by 11 | Viewed by 4942

Abstract

X-ray crystallography remains a powerful method to gain atomistic insights into the catalytic and regulatory functions of RNA molecules. However, the technique requires the preparation of diffraction-quality crystals. This is often a resource- and time-consuming venture because RNA crystallization is hindered by the [...] Read more.

X-ray crystallography remains a powerful method to gain atomistic insights into the catalytic and regulatory functions of RNA molecules. However, the technique requires the preparation of diffraction-quality crystals. This is often a resource- and time-consuming venture because RNA crystallization is hindered by the conformational heterogeneity of RNA, as well as the limited opportunities for stereospecific intermolecular interactions between RNA molecules. The limited success at crystallization explains in part the smaller number of RNA-only structures in the Protein Data Bank. Several approaches have been developed to aid the formation of well-ordered RNA crystals. The majority of these are construct-engineering techniques that aim to introduce crystal contacts to favor the formation of well-diffracting crystals. A typical example is the insertion of tetraloop–tetraloop receptor pairs into non-essential RNA segments to promote intermolecular association. Other methods of promoting crystallization involve chaperones and crystallization-friendly molecules that increase RNA stability and improve crystal packing. In this review, we discuss the various techniques that have been successfully used to facilitate crystal packing of RNA molecules, recent advances in construct engineering, and directions for future research in this vital aspect of RNA crystallography. Full article

(This article belongs to the Special Issue Nucleic Acid Crystallography)

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10 pages, 3191 KiB

Open AccessEditor’s ChoiceCommunication

Investigation on the Effects of Grain Boundary on Deformation Behavior of Bicrystalline Pillar by Crystal Plasticity Finite Element Method

by Hui Zhou, Pei Wang and Shanping Lu

Crystals 2021, 11(8), 923; https://doi.org/10.3390/cryst11080923 - 9 Aug 2021

Cited by 6 | Viewed by 2816

Abstract

A dislocation density–grain boundary interaction scheme coupled with the dislocation density-based crystalline plasticity finite element method has been established and used to investigate the deformation behavior of bicrystalline pillars with the same grain boundary misorientation angle but different crystal orientations. It is found [...] Read more.

A dislocation density–grain boundary interaction scheme coupled with the dislocation density-based crystalline plasticity finite element method has been established and used to investigate the deformation behavior of bicrystalline pillars with the same grain boundary misorientation angle but different crystal orientations. It is found that the angle between the activated slip systems, which is determined by the crystal orientations, rather than the grain boundary misorientation angle, influences the interactions between the plastic slip and the grain boundary, which further influence the heterogeneous deformation of bicrystalline specimens. Full article

(This article belongs to the Special Issue Crystal Plasticity (Volume II))

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13 pages, 31239 KiB

Open AccessEditor’s ChoiceArticle

Heterogeneous Crystal Nucleation from the Melt in Polyethylene Oxide Droplets on Graphite: Kinetics and Microscopic Structure

by Muhammad Tariq, Thomas Thurn-Albrecht and Oleksandr Dolynchuk

Crystals 2021, 11(8), 924; https://doi.org/10.3390/cryst11080924 - 9 Aug 2021

Cited by 8 | Viewed by 3256

Abstract

It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation [...] Read more.

It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation in an ensemble of polyethylene oxide (PEO) droplets on graphite and on amorphous polystyrene (PS). The optical microscopy measurements during cooling with a constant rate explicitly evidenced that the graphite substrate enhances the nucleation kinetics, as crystallization occurred at approximately an 11 °C higher temperature than on PS due to changes in the interactions at the solid interface. This observation allowed us to conclude that graphite induces heterogeneous nucleation in PEO. By employing the classical nucleation theory for analysis of the data with reference to the amorphous PS substrate, the obtained results indicated that the crystal nuclei with contact angles in the range of 100–117° were formed at the graphite interface. Furthermore, we show that heterogeneous nucleation led to a preferred orientation of PEO crystals on graphite, whereas PEO crystals on PS had isotropic orientation. The difference in crystal orientations on the two substrates was also confirmed with AFM, which showed only edge-on lamellae in PEO droplets on graphite compared to unoriented lamellae on PS. Full article

(This article belongs to the Topic Polymer Crystallization)

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22 pages, 7297 KiB

Open AccessEditor’s ChoiceArticle

Investigation of Mid-Infrared Broadband Second-Harmonic Generation in Non-Oxide Nonlinear Optic Crystals

by Ilhwan Kim, Donghwa Lee and Kwang Jo Lee

Crystals 2021, 11(8), 921; https://doi.org/10.3390/cryst11080921 - 8 Aug 2021

Cited by 6 | Viewed by 3903

Abstract

The mid-infrared (mid-IR) continuum generation based on broadband second harmonic generation (SHG) (or difference frequency generation) is of great interest in a wide range of applications such as free space communications, environmental monitoring, thermal imaging, high-sensitivity metrology, gas sensing, and molecular fingerprint spectroscopy. [...] Read more.

The mid-infrared (mid-IR) continuum generation based on broadband second harmonic generation (SHG) (or difference frequency generation) is of great interest in a wide range of applications such as free space communications, environmental monitoring, thermal imaging, high-sensitivity metrology, gas sensing, and molecular fingerprint spectroscopy. The second-order nonlinear optic (NLO) crystals have been spotlighted as a material platform for converting the wavelengths of existing lasers into the mid-IR spectral region or for realizing tunable lasers. In particular, the spectral coverage could be extended to ~19 µm with non-oxide NLO crystals. In this paper, we theoretically and numerically investigated the broadband SHG properties of non-oxide mid-IR crystals in three categories: chalcopyrite semiconductors, defect chalcopyrite, and orthorhombic ternary chalcogenides. The technique is based on group velocity matching between interacting waves in addition to birefringent phase matching. We will describe broadband SHG characteristics in terms of beam propagation directions, spectral positions of resonance, effective nonlinearities, spatial walk-offs between interacting beams, and spectral bandwidths. The results will show that the spectral bandwidths of the fundamental wave allowed for broadband SHG to reach several hundreds of nm. The corresponding SH spectral range spans from 1758.58 to 4737.18 nm in the non-oxide crystals considered in this study. Such broadband SHG using short pulse trains can potentially be applied to frequency up-conversion imaging in the mid-IR region, in information transmission, and in nonlinear optical signal processing. Full article

(This article belongs to the Special Issue Advances in Middle Infrared Laser Crystals and Its Applications)

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16 pages, 4246 KiB

Open AccessEditor’s ChoiceArticle

Crystal Growth on Cenospheres from High-Calcium Fly Ash

by Sorachon Yoriya and Phattarathicha Tepsri

Crystals 2021, 11(8), 919; https://doi.org/10.3390/cryst11080919 - 7 Aug 2021

Cited by 6 | Viewed by 2990

Abstract

This work presents a study of cenosphere separation from lignite high-calcium (~24 wt.%) fly ash by centrifugal method; this is the first report for Mae Moh, Thailand, fly ash with this high calcium content using this technique. The effect of centrifugal parameters on [...] Read more.

This work presents a study of cenosphere separation from lignite high-calcium (~24 wt.%) fly ash by centrifugal method; this is the first report for Mae Moh, Thailand, fly ash with this high calcium content using this technique. The effect of centrifugal parameters on cenosphere yield and properties were investigated. Those properties include physical properties, morphology, chemical composition, and mineral phases. The recovery yields are in the range of 0.34–0.64%, approximately one third of the yield obtained from the general gravity settling method. Density, particle size, and morphology of the collected cenospheres appeared to be independent of sequence of the applied speeds and times. Interrelation of chemical composition and mineral phases was established, with the focus on calcium carbonate formation on cenosphere surface and crystallite size study. The study has revealed the preferential formation of calcite–(104) peak is observed–by cenospheres, with stable growth behavior of crystallite sizes obtained from all the centrifugal conditions. The result was compared to that obtained from the sink-float method for a better insight. The influence and limitation of the centrifugal method, the varied parameters, and the relevant reaction pathways on crystal growth process in terms of important dissolving species (i.e., Ca²⁺ and CO₃²⁻) behavior in the ash suspension were discussed. Full article

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13 pages, 2901 KiB

Open AccessEditor’s ChoiceArticle

Topological Defect-Guided Regular Stacking of Focal Conic Domains in Hybrid-Aligned Smectic Liquid Crystal Shells

by JungHyun Noh and Jan P. F. Lagerwall

Crystals 2021, 11(8), 913; https://doi.org/10.3390/cryst11080913 - 4 Aug 2021

Cited by 6 | Viewed by 3396

Abstract

We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at [...] Read more.

We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at the thinnest and thickest points, respectively. On cooling from N to SmA, the symmetry axis connecting the defects gradually reorients from along gravity to perpendicular to it, reversibly and continuously, if the LC and aqueous phase are density matched at the N-SmA transition. This suggests reduced density near the defects—reflecting a local reduction in order—under the strong confinement with antagonistic boundary conditions. In the SmA phase, a regular array of focal conic domains (FCDs) develops, templated in position and orientation by the +1 defect at the thinnest point. Around this defect, a single complete toroidal FCD always develops, surrounded by incomplete FCDs. In contrast to similar FCD arrangements on flat aqueous interfaces, this is a stable situation, since the two +1 defects are required by the spherical topology. Our results demonstrate how the topological defects of LC shells can be used to template complex self-organized structures. With a suitable adaption of the LC chemistry, shells might serve as a basis for producing solid particles with complex yet highly regular morphologies. Full article

(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)

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11 pages, 2099 KiB

Open AccessEditor’s ChoiceArticle

Optofluidic Platform Based on Liquid Crystals in X-Cut Lithium Niobate: Thresholdless All-Optical Response

by Fabrizio Ciciulla, Annamaria Zaltron, Riccardo Zamboni, Cinzia Sada, Francesco Simoni, Victor Yu. Reshetnyak and Liana Lucchetti

Crystals 2021, 11(8), 908; https://doi.org/10.3390/cryst11080908 - 2 Aug 2021

Cited by 10 | Viewed by 2943

Abstract

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a [...] Read more.

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a x-cut crystal closed by a z-cut crystal on the top. In this way, the light-induced photovoltaic field is not uniform inside the liquid crystal layer and therefore the conditions for a thresholdless reorientation are realized. We performed simulations of the photovoltaic effect based on the well assessed model for Lithium Niobate, showing that not uniform orientation and value of the field should be expected inside the microchannel. In agreement with the re-orientational properties of nematic liquid crystals, experimental data confirm the expected thresholdless behaviour. The observed liquid crystal response exhibits two different regimes and the response time shows an unusual dependence on light intensity, both features indicating the presence of additional photo-induced fields appearing above a light intensity of 10⁷ W/m². Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Online Conference on Crystals)

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22 pages, 28654 KiB

Open AccessEditor’s ChoiceArticle

Intramolecular Hydrogen Bond, Hirshfeld Analysis, AIM; DFT Studies of Pyran-2,4-dione Derivatives

by Ahmed T. A. Boraei, Matti Haukka, Ahmed A. M. Sarhan, Saied M. Soliman and Assem Barakat

Crystals 2021, 11(8), 896; https://doi.org/10.3390/cryst11080896 - 30 Jul 2021

Cited by 14 | Viewed by 4115

Abstract

Intra and intermolecular interactions found in the developed crystals of the synthesized py-ron-2,4-dione derivatives play crucial rules in the molecular conformations and crystal stabili-ties, respectively. In this regard, Hirshfeld calculations were used to quantitatively analyze the different intermolecular interactions in the crystal structures [...] Read more.

Intra and intermolecular interactions found in the developed crystals of the synthesized py-ron-2,4-dione derivatives play crucial rules in the molecular conformations and crystal stabili-ties, respectively. In this regard, Hirshfeld calculations were used to quantitatively analyze the different intermolecular interactions in the crystal structures of some functionalized py-ran-2,4-dione derivatives. The X-ray structure of pyran-2,4-dione derivative namely (3E,3′E)-3,3′-((ethane-1,2-diylbis(azanediyl))bis(phenylmethanylylidene))bis(6-phenyl-2H-pyran-2,4(3H)-dione) was determined. It crystallized in the monoclinic crystal system and C2/c space group with unit cell parameters: a = 14.0869(4) Å, b = 20.9041(5) Å, c = 10.1444(2) Å and β = 99.687(2)°. Generally, the H…H, H…C, O…H and C…C contacts are the most important interactions in the molecular packing of the studied pyran-2,4-diones. The molecular structure of these compounds is stabilized by intramolecular O…H hydrogen bond. The nature and strength of the O…H hy-drogen bonds were analyzed using atoms in molecules calculations. In all compounds, the O…H hydrogen bond belongs to closed-shell interactions where the interaction energies are higher at the optimized geometry than the X-ray one due to the shortening in the A…H distance as a con-sequence of the geometry optimization. These compounds have polar characters with different charged regions which explored using molecular electrostatic potential map. Their natural charges, reactivity descriptors and NMR chemical shifts were computed, discussed and compared. Full article

(This article belongs to the Special Issue New Trends in Crystals at Saudi Arabia)

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6 pages, 1236 KiB

Open AccessEditor’s ChoiceArticle

Seeded Growth of Type-II Na₂₄Si₁₃₆ Clathrate Single Crystals

by Haruhiko Morito, Hisanori Yamane, Rie Y. Umetsu and Kozo Fujiwara

Crystals 2021, 11(7), 808; https://doi.org/10.3390/cryst11070808 - 12 Jul 2021

Cited by 11 | Viewed by 2726

Abstract

Type-II Na₂₄Si₁₃₆ clathrate octahedral single crystals surrounded by {111} facets were grown by evaporating Na from a molten mixture of Na₄Si₄ and Na₉Sn₄ at 823 K for 12 h. One of the obtained single [...] Read more.

Type-II Na₂₄Si₁₃₆ clathrate octahedral single crystals surrounded by {111} facets were grown by evaporating Na from a molten mixture of Na₄Si₄ and Na₉Sn₄ at 823 K for 12 h. One of the obtained single crystals was used as a seed for the following single crystal growth of the type-II clathrate using the same method. The single crystal grown on the seed maintained the octahedral shape. The weight of the crystal grown with the seed was increased from 0.6 to 30.4 mg by repeating the seeded growth and was proportional to the surface area of the seed crystal. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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16 pages, 3517 KiB

Open AccessEditor’s ChoiceArticle

Comparison of the Effect of the Amino Acids on Spontaneous Formation and Transformation of Calcium Phosphates

by Ina Erceg, Nadica Maltar-Strmečki, Darija Domazet Jurašin, Vida Strasser, Marija Ćurlin, Daniel Mark Lyons, Borna Radatović, Nives Matijaković Mlinarić, Damir Kralj and Maja Dutour Sikirić

Crystals 2021, 11(7), 792; https://doi.org/10.3390/cryst11070792 - 7 Jul 2021

Cited by 15 | Viewed by 3966

Abstract

Understanding the effect that specific amino acids (AA) exert on calcium phosphate (CaPs) formation is proposed as a way of providing deeper insight into CaPs’ biomineralization and enabling the design of tailored-made additives for the synthesis of functional materials. Despite a number of [...] Read more.

Understanding the effect that specific amino acids (AA) exert on calcium phosphate (CaPs) formation is proposed as a way of providing deeper insight into CaPs’ biomineralization and enabling the design of tailored-made additives for the synthesis of functional materials. Despite a number of investigations, the role of specific AA is still unclear, mostly because markedly different experimental conditions have been employed in different studies. The aim of this paper was to compare the influence of different classes of amino acids, charged (aspartic acid, Asp and lysine, Lys), polar (asparagine, Asn and serine, Ser) and non-polar (phenylalanine, Phe) on CaPs formation and transformation in conditions similar to physiological conditions. The precipitation process was followed potentiometrically, while Fourier transform infrared spectroscopy, powder X-ray diffraction, electron paramagnetic spectroscopy (EPR), scanning and transmission electron microscopy were used for the characterization of precipitates. Except for Phe, all investigated AAs inhibited amorphous calcium phosphate (ACP) transformation, with Ser being the most efficient inhibitor. In all systems, ACP transformed in calcium-deficient hydroxyapatite (CaDHA). However, the size of crystalline domains was affected, as well as CaDHA morphology. In EPR spectra, the contribution of different radical species with different proportions in diverse surroundings, depending on the type of AA present, was observed. The obtained results are of interest for the preparation of functionalized CaPs’, as well as for the understanding of their formation in vivo. Full article

(This article belongs to the Special Issue Green Approach in Synthesis of Bio-Inspired Materials)

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19 pages, 4967 KiB

Open AccessEditor’s ChoiceArticle

Studying the Damage Evolution and the Micro-Mechanical Response of X8CrMnNi16-6-6 TRIP Steel Matrix and 10% Zirconia Particle Composite Using a Calibrated Physics and Crystal-Plasticity-Based Numerical Simulation Model

by Faisal Qayyum, Sergey Guk and Ulrich Prahl

Crystals 2021, 11(7), 759; https://doi.org/10.3390/cryst11070759 - 29 Jun 2021

Cited by 19 | Viewed by 4772

Abstract

The mechanical behavior of newly developed composite materials is dependent on several underlying microstructural phenomena. In this research, a periodic 2D geometry of cast X8CrMnNi16-6-6 steel and 10% zirconia composite is virtually constructed by adopting microstructural attributes from literature. A physics-based crystal plasticity [...] Read more.

The mechanical behavior of newly developed composite materials is dependent on several underlying microstructural phenomena. In this research, a periodic 2D geometry of cast X8CrMnNi16-6-6 steel and 10% zirconia composite is virtually constructed by adopting microstructural attributes from literature. A physics-based crystal plasticity model with ductile damage criterion is used for defining the austenitic steel matrix. The zirconia particles are assigned elastic material model with brittle damage criterion. Monotonic quasi-static tensile load is applied up to 17% of total strain. The simulation results are analyzed to extract the global and local deformation, transformation, and damage behavior of the material. The comprehensively constructed simulation model yields the interdependence of the underlaying microstructural deformation phenomena. The local results are further analyzed based on the interlocked and free regions to establish the influence of zirconia particles on micro-mechanical deformation and damage in the metastable austenite matrix. The trends and patterns of local strain and damage predicted by the simulation model results match the previously carried out in-situ tensile tests on similar materials. Full article

(This article belongs to the Special Issue Combinatorial and High-Throughput Discovery of New Metallic Materials)

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10 pages, 3831 KiB

Open AccessEditor’s ChoiceArticle

Multi-View 2D/3D Switchable Display with Cylindrical Liquid Crystal Lens Array

by Fan Chu, Di Wang, Chao Liu, Lei Li and Qiong-Hua Wang

Crystals 2021, 11(6), 715; https://doi.org/10.3390/cryst11060715 - 21 Jun 2021

Cited by 24 | Viewed by 4503

Abstract

We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) [...] Read more.

We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) electrode, and bottom periodic strip ITO electrodes. In the voltage-off state, the cylindrical LC lens array is equivalent to a transparent glass substrate and the viewers can see a clear 2D image. In the 3D mode, the cylindrical LC lens array can be used as a cylindrical lens array under a suitable operating voltage. As a result, the 2D and 3D images can be switched according to the state of the cylindrical LC lens array. The experimental result shows that the 2D/3D switchable display with the cylindrical LC lens array has a wider viewing angle, has no moiré pattern, and is much thinner compared to the other 2D/3D switchable display devices. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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15 pages, 3413 KiB

Open AccessEditor’s ChoiceArticle

A Phononic Crystal with Differently Configured Double Defects for Broadband Elastic Wave Energy Localization and Harvesting

by Soo-Ho Jo and Byeng D. Youn

Crystals 2021, 11(6), 643; https://doi.org/10.3390/cryst11060643 - 5 Jun 2021

Cited by 32 | Viewed by 4855

Abstract

Several previous studies have been dedicated to incorporating double defect modes of a phononic crystal (PnC) into piezoelectric energy harvesting (PEH) systems to broaden the bandwidth. However, these prior studies are limited to examining an identical configuration of the double defects. Therefore, this [...] Read more.

Several previous studies have been dedicated to incorporating double defect modes of a phononic crystal (PnC) into piezoelectric energy harvesting (PEH) systems to broaden the bandwidth. However, these prior studies are limited to examining an identical configuration of the double defects. Therefore, this paper aims to propose a new design concept for PnCs that examines differently configured double defects for broadband elastic wave energy localization and harvesting. For example, a square-pillar-type unit cell is considered and a defect is considered to be a structure where one piezoelectric patch is bonded to a host square lattice in the absence of a pillar. When the double defects introduced in a PnC are sufficiently distant from each other to implement decoupling behaviors, each defect oscillates like a single independent defect. Here, by differentiating the geometric dimensions of two piezoelectric patches, the defects’ dissimilar equivalent inertia and stiffness contribute to individually manipulating defect bands that correspond to each defect. Hence, with adequately designed piezoelectric patches that consider both the piezoelectric effects on shift patterns of defect bands and the characteristics for the output electric power obtained from a single-defect case, we can successfully localize and harvest the elastic wave energy transferred in broadband frequencies. Full article

(This article belongs to the Special Issue Applications of Phononic Crystals & Acoustic Metamaterials)

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