Crystals

2 pages, 138 KiB

Open AccessCorrection

Correction: Jindal, P.C. A New Method for Evaluating the Indentation Toughness of Hardmetals. Crystals 2018, 8, 197

by Prem C. Jindal

Crystals 2020, 10(12), 1165; https://doi.org/10.3390/cryst10121165 - 21 Dec 2020

Viewed by 1610

Abstract

The authors wish to make the following correction to the paper [...] Full article

12 pages, 28099 KiB

Open AccessArticle

Numerical Investigation of High-Purity Entangled Photon-Pair Generation in Ba₃Mg₃(BO₃)₃F₃ Crystals

by Donghwa Lee, Ilhwan Kim and Kwang Jo Lee

Crystals 2020, 10(12), 1164; https://doi.org/10.3390/cryst10121164 - 21 Dec 2020

Cited by 1 | Viewed by 2314

Abstract

We investigate the high-purity entangled photon pair generation in a recently developed borate crystal, Ba₃Mg₃(BO₃)₃F₃. The technique is based on the spontaneous parametric down-conversion under the extended phase matching (EPM), where the phase [...] Read more.

We investigate the high-purity entangled photon pair generation in a recently developed borate crystal, Ba₃Mg₃(BO₃)₃F₃. The technique is based on the spontaneous parametric down-conversion under the extended phase matching (EPM), where the phase matching and the group velocity matching between the interacting photons are satisfied simultaneously in bulk crystals with point symmetry of orthorhombic mm2 (thus showing biaxial birefringence). We will discuss all the theoretical aspects required for the generation of photon pairs in mm2 biaxial crystals, which are much more complex than the cases of uniaxial crystals (e.g., β-BaB₂O₄ and LiNbO₃) and periodically poled crystals that are widely used in the field. Our study includes theoretical and numerical investigations of two types of EPM and their corresponding effective nonlinearities and spatial walk-offs. The results show that two types of EPM are satisfied over the specific range in the direction of pump wave vector, corresponding to its spectral ranges of 876.15–1052.77 nm for Type I and 883.92–914.33 nm for Type II. The joint spectral analyses show that photon-pairs can be generated with high purities of 0.997 with a proper pump filtering (for Type II), and 0.833 even without pump filtering (for Type I). Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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36 pages, 9013 KiB

Open AccessReview

Heteroepitaxial Growth of III-V Semiconductors on Silicon

by Jae-Seong Park, Mingchu Tang, Siming Chen and Huiyun Liu

Crystals 2020, 10(12), 1163; https://doi.org/10.3390/cryst10121163 - 21 Dec 2020

Cited by 74 | Viewed by 9668

Abstract

Monolithic integration of III-V semiconductor devices on Silicon (Si) has long been of great interest in photonic integrated circuits (PICs), as well as traditional integrated circuits (ICs), since it provides enormous potential benefits, including versatile functionality, low-cost, large-area production, and dense integration. However, [...] Read more.

Monolithic integration of III-V semiconductor devices on Silicon (Si) has long been of great interest in photonic integrated circuits (PICs), as well as traditional integrated circuits (ICs), since it provides enormous potential benefits, including versatile functionality, low-cost, large-area production, and dense integration. However, the material dissimilarity between III-V and Si, such as lattice constant, coefficient of thermal expansion, and polarity, introduces a high density of various defects during the growth of III-V on Si. In order to tackle these issues, a variety of growth techniques have been developed so far, leading to the demonstration of high-quality III-V materials and optoelectronic devices monolithically grown on various Si-based platform. In this paper, the recent advances in the heteroepitaxial growth of III-V on Si substrates, particularly GaAs and InP, are discussed. After introducing the fundamental and technical challenges for III-V-on-Si heteroepitaxy, we discuss recent approaches for resolving growth issues and future direction towards monolithic integration of III-V on Si platform. Full article

(This article belongs to the Special Issue Semiconductor Heteroepitaxy)

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8 pages, 3213 KiB

Open AccessArticle

Heterogeneous Deformation Behavior of Cu-Ni-Si Alloy by Micro-Size Compression Testing

by Sari Yanagida, Takashi Nagoshi, Akiyoshi Araki, Tso-Fu Mark Chang, Chun-Yi Chen, Equo Kobayashi, Akira Umise, Hideki Hosoda, Tatsuo Sato and Masato Sone

Crystals 2020, 10(12), 1162; https://doi.org/10.3390/cryst10121162 - 21 Dec 2020

Cited by 2 | Viewed by 2514

Abstract

The aim of this study is to investigate a characteristic deformation behavior of a precipitation strengthening-type Cu-Ni-Si alloy (Cu-2.4Ni-0.51Si-9.3Zn-0.15Sn-0.13Mg) by microcompression specimens. Three micropillars with a square cross-section of 20 × 20 × 40 μm³ were fabricated by focused ion beam (FIB) [...] Read more.

The aim of this study is to investigate a characteristic deformation behavior of a precipitation strengthening-type Cu-Ni-Si alloy (Cu-2.4Ni-0.51Si-9.3Zn-0.15Sn-0.13Mg) by microcompression specimens. Three micropillars with a square cross-section of 20 × 20 × 40 μm³ were fabricated by focused ion beam (FIB) micromachining apparatus and tested by a machine specially designed for microsized specimens. The three pillars were deformed complicatedly and showed different yield strengths depending on the crystal orientation. The micromechanical tests revealed work hardening by the precipitation clearly. Electron backscattered diffraction analysis of a deformed specimen showed a gradual rotation of grain axis at the grain boundaries after the compression test. Full article

(This article belongs to the Special Issue Crystal Plasticity)

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15 pages, 5999 KiB

Open AccessArticle

Chiral Photoresponsive Liquid Crystalline Materials Derived from Cyanoazobenzene Central Core: Effect of UV Light Illumination on Mesomorphic Behavior

by Anna Poryvai, Alexej Bubnov and Michal Kohout

Crystals 2020, 10(12), 1161; https://doi.org/10.3390/cryst10121161 - 21 Dec 2020

Cited by 6 | Viewed by 2602

Abstract

One of the most frequently utilized liquid crystalline (LC) materials is a rod-like (calamitic) compound 4-cyano-4′-pentylbiphenyl (5-CB). The main objective of this work is to enhance its functionality by introducing a photoresponsive diazenyl spacer in the aromatic core and replace the non-chiral pentyl [...] Read more.

One of the most frequently utilized liquid crystalline (LC) materials is a rod-like (calamitic) compound 4-cyano-4′-pentylbiphenyl (5-CB). The main objective of this work is to enhance its functionality by introducing a photoresponsive diazenyl spacer in the aromatic core and replace the non-chiral pentyl chain with various chiral alkyl carboxylate units. The mesomorphic properties of the prepared materials have been studied using polarizing optical microscopy and differential scanning calorimetry. It has been found that materials with an extended aromatic system possess the liquid crystalline behavior. The studied LC materials have shown mesophases at lower temperatures than previously reported analogous substances. Furthermore, one of them exhibits a chiral orthogonal frustrated twist grain boundary smectic phase, which has not been previously observed for this structural type of materials. We also investigated photoresponse of the mesophases under illumination with UV-light (365 nm) using a polarizing optical microscope. A non-conventional photoresponse of the prepared materials in a crystalline phase is presented and discussed. Full article

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

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10 pages, 1129 KiB

Open AccessArticle

Effects of the Domain Wall Conductivity on the Domain Formation under AFM-Tip Voltages in Ion-Sliced LiNbO₃ Films

by Radmir Gainutdinov and Tatyana Volk

Crystals 2020, 10(12), 1160; https://doi.org/10.3390/cryst10121160 - 19 Dec 2020

Cited by 7 | Viewed by 2594

Abstract

The specified domain patterns were written by AFM-tip voltages in LiNbO₃ films composing LNOI (LiNbO₃-on-insulator). The domain wall conductivity (DWC) was estimated in the written patterns. This estimate was based on the effects of load resistors R_L inserted between [...] Read more.

The specified domain patterns were written by AFM-tip voltages in LiNbO₃ films composing LNOI (LiNbO₃-on-insulator). The domain wall conductivity (DWC) was estimated in the written patterns. This estimate was based on the effects of load resistors R_L inserted between DWs and the ground, on the features of occurring domains. In this case, the domain formation is controlled by the ratio between R_L and the DWs’ resistance R_DW. Starting from the comparison of patterns appearing at different R_L, the value of R_DW in a specified pattern was estimated. The corresponding DWC is of σ_DW ≈ 10⁻³ (Ohm cm)⁻¹ which exceeds the tabular bulk conductivity of LiNbO₃ by no less than twelve orders of magnitude. A small DW inclination angle of (10⁻⁴)⁰ responsible for this DWC is not caused by any external action and characterizes the domain frontal growth under an AFM-tip voltage. Full article

(This article belongs to the Special Issue New Trends in Lithium Niobate: From Bulk to Nanocrystals)

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12 pages, 4198 KiB

Open AccessArticle

The Study on Structural and Photoelectric Properties of Zincblende InGaN via First Principles Calculation

by Juan Song, Zijiang Luo, Xuefei Liu, Ershi Li, Chong Jiang, Zechen Huang, Jiawei Li, Xiang Guo, Zhao Ding and Jihong Wang

Crystals 2020, 10(12), 1159; https://doi.org/10.3390/cryst10121159 - 19 Dec 2020

Cited by 6 | Viewed by 2822

Abstract

In this paper, the structure and photoelectric characteristics of zincblende In_xGa_1−xN alloys are systematically calculated and analyzed based on the density functional theory, including the lattice constant, band structure, distribution of electronic states, dielectric function, and absorption coefficient. [...] Read more.

In this paper, the structure and photoelectric characteristics of zincblende In_xGa_1−xN alloys are systematically calculated and analyzed based on the density functional theory, including the lattice constant, band structure, distribution of electronic states, dielectric function, and absorption coefficient. The calculation results show that with the increase in x, the lattice constants and the supercell volume increase, whereas the bandgap tends to decrease, and In_xGa_1−xN alloys are direct band gap semiconductor materials. In addition, the imaginary part of the dielectric function and the absorption coefficient are found to redshift with the increase in indium composition, expanding the absorption range of visible light. By analyzing the lattice constants, polarization characteristics, and photoelectric properties of the In_xGa_1−xN systems, it is observed that zincblende In_xGa_1−xN can be used as an alternative material to replace the channel layer of wurtzite In_xGa_1−xN heterojunction high electron mobility transistor (HEMT) devices to achieve the manufacture of HEMT devices with higher power and higher frequency. In addition, it also provides a theoretical reference for the practical application of In_xGa_1−xN systems in optoelectronic devices. Full article

(This article belongs to the Special Issue First-Principles Simulation—Nano-Theory)

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15 pages, 3218 KiB

Open AccessArticle

Evaluation of Novel Glycerol/PEO Gel Polymer Electrolytes for Non-Toxic Dye-Sensitized Solar Cells with Natural Dyes Regarding Long-Term Stability and Reproducibility

by Jan Lukas Storck, Marius Dotter, Bennet Brockhagen and Timo Grothe

Crystals 2020, 10(12), 1158; https://doi.org/10.3390/cryst10121158 - 19 Dec 2020

Cited by 11 | Viewed by 2927

Abstract

Alongside efficiency, long-term stability of dye-sensitized solar cells (DSSCs) is a key factor regarding their commercialization. One suitable and cost-effective method to increase the long-term stability is to prevent leakage and evaporation of the electrolyte by gelling it with polymers such as poly(ethylene [...] Read more.

Alongside efficiency, long-term stability of dye-sensitized solar cells (DSSCs) is a key factor regarding their commercialization. One suitable and cost-effective method to increase the long-term stability is to prevent leakage and evaporation of the electrolyte by gelling it with polymers such as poly(ethylene oxide) (PEO) and gaining a gel polymer electrolyte (GPE). In this study, a GPE based on PEO and glycerol is investigated for the first time as electrolyte for environmentally friendly DSSCs with natural dyes. To evaluate the novel glycerol/PEO GPE, the ionic conductivity and resulting efficiency progressions of DSSCs were measured for 75 days. Different molecular weights (MWs) of PEO and blending with poly(vinylidene fluoride) (PVDF) had negligible impact on efficiencies. 17 wt% PEO was found to be more suitable than lower concentrations and resulted in a relatively high efficiency over 75 days. A glycerol electrolyte without PEO had higher ionic conductivity and achieved higher efficiencies as well but leaked from the unsealed DSSCs. In addition, the reproducibility was examined especially, which appeared to be reduced by considerable differences between identical DSSCs and between measurements of the same DSSC at different times. This emphasizes the relevance of studying multiple DSSC per sample to ensure reliable results. Full article

(This article belongs to the Special Issue A 10 Years Journey: Chemical, Physical, and Biological Properties and Applications of Crystals)

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11 pages, 2689 KiB

Open AccessArticle

Designing (Ultra)Fine-Grained High-Entropy Alloys by Spark Plasma Sintering and Equal-Channel Angular Pressing

by Lisa-Marie Rymer, Thomas Lindner, Philipp Frint, Martin Löbel and Thomas Lampke

Crystals 2020, 10(12), 1157; https://doi.org/10.3390/cryst10121157 - 18 Dec 2020

Cited by 9 | Viewed by 2541

Abstract

Single-phase, face-centered cubic (FCC) high-entropy alloys (HEA) are promising materials for future applications. In order to improve the mechanical properties, especially the tensile strength of these materials, this study focuses on the combination of spark plasma sintering (SPS) and equal-channel angular pressing (ECAP). [...] Read more.

Single-phase, face-centered cubic (FCC) high-entropy alloys (HEA) are promising materials for future applications. In order to improve the mechanical properties, especially the tensile strength of these materials, this study focuses on the combination of spark plasma sintering (SPS) and equal-channel angular pressing (ECAP). The initial fine-grained microstructure produced by SPS is further refined by ECAP in a 90°-die. Optical microscopy and electron backscatter diffraction (EBSD) confirm this considerable grain refinement, leads to a grain size below 1 µm after 1 ECAP pass. An alternating arrangement of fine-grained areas and much coarser regions, aligned under an angle of approximately 27°, is found. Moreover, a first microstructural investigation of the twin structure is conducted. The mechanical behavior was investigated by hardness measurements and tensile testing. Both the hardness and tensile strength are remarkably increased after ECAP. In contrast, the uniform elongation and elongation at fracture are significantly reduced due to the strengthening mechanisms of strain hardening and grain refinement. It is concluded that the combination of SPS and ECAP is an attractive approach for designing (ultra)fine-grained HEAs with superior properties. The investigated techniques could be applied to understand the underlying microstructural mechanisms. Full article

(This article belongs to the Special Issue Deformation Mechanisms in High Entropy Alloys)

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7 pages, 4289 KiB

Open AccessArticle

Microstructure and Material Properties of Ti-15mass%Nb Alloy after Gas Nitriding and Quenching Process

by Yoshikazu Mantani, Kentaro Shimada and Naoki Eguchi

Crystals 2020, 10(12), 1156; https://doi.org/10.3390/cryst10121156 - 18 Dec 2020

Cited by 1 | Viewed by 2477

Abstract

The α′ martensite of Ti-15mass%Nb alloy exhibits high internal friction with high damping properties. However, its structure is smoother than the α + β structure. Therefore, a hardened surface layer is required for abrasion resistance. This study fabricated a martensite structure inside the [...] Read more.

The α′ martensite of Ti-15mass%Nb alloy exhibits high internal friction with high damping properties. However, its structure is smoother than the α + β structure. Therefore, a hardened surface layer is required for abrasion resistance. This study fabricated a martensite structure inside the nitriding layer by quenching, after gas nitriding at 1023 and 1223 K. Vickers hardness test, X-ray diffraction, scanning electron microscopy (SEM), and SEM-energy dispersive X-ray (SEM-EDX) measurements from the surface to the inside were made after the heat treatment process. In addition, the Young’s modulus and internal friction were calculated from the damping analysis. The α-TiN_0.3 and β phase region was formed at approximately 80 µm from the surface at 1023 and 1223 K, and it was hardened. The internal friction of the gas nitriding and quenching specimens at 1023 and 1223 K was relatively high, though it did not reach that of the as-quenched specimen owing to the influence of the surface structure. From these results, it is considered that these material property values of the alloy can be controlled using the nitriding and quenching processes. Full article

(This article belongs to the Special Issue Thermomechanical Processing and Microstructure Control of Ti Alloys)

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17 pages, 6895 KiB

Open AccessArticle

Mueller Matrix Polarimetric Imaging Analysis of Optical Components for the Generation of Cylindrical Vector Beams

by Guadalupe López-Morales, María del Mar Sánchez-López, Ángel Lizana, Ignacio Moreno and Juan Campos

Crystals 2020, 10(12), 1155; https://doi.org/10.3390/cryst10121155 - 18 Dec 2020

Cited by 17 | Viewed by 4235

Abstract

In this work, we performed a Mueller matrix imaging analysis of two commercial optical components usually employed to generate and manipulate vector beams—a radial polarizer and a liquid-crystal q-plate. These two elements generate vector beams by different polarization mechanisms—polarizance and retardance, respectively. [...] Read more.

In this work, we performed a Mueller matrix imaging analysis of two commercial optical components usually employed to generate and manipulate vector beams—a radial polarizer and a liquid-crystal q-plate. These two elements generate vector beams by different polarization mechanisms—polarizance and retardance, respectively. The quality of the vector beams relies on the quality of the device that generates them. Therefore, it is of interest to apply the well-established polarimetric imaging techniques to evaluate these optical components by identifying their spatial homogeneity in diattenuation, polarizance, depolarization, and retardance, as well as the spatial variation of the angles of polarizance and retardance vectors. For this purpose, we applied a customized imaging Mueller matrix polarimeter based on liquid-crystal retarders and a polarization camera. Experimental results were compared to the numerical simulations, considering the theoretical Mueller matrix. This kind of polarimetric characterization could be very helpful to the manufacturers and users of these devices. Full article

(This article belongs to the Special Issue Patterned-Liquid-Crystal for Novel Displays)

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12 pages, 4184 KiB

Open AccessArticle

Study of Texture Analysis on Asymmetric Cryorolled and Annealed CoCrNi Medium Entropy Alloy

by Yuze Wu, Juan Liu, Laxman Bhatta, Charlie Kong and Hailiang Yu

Crystals 2020, 10(12), 1154; https://doi.org/10.3390/cryst10121154 - 18 Dec 2020

Cited by 6 | Viewed by 4675

Abstract

CoCrNi equiatomic medium entropy alloy sheets were prepared by asymmetric rolling, cryorolling, and asymmetric cryorolling. The asymmetric cryorolled samples exhibited a noteworthy ultra-fine-grain heterogeneous lamella structure. The microstructure and corresponding hardness obtained by different rolling processes and subsequent annealing are compared. It can [...] Read more.

CoCrNi equiatomic medium entropy alloy sheets were prepared by asymmetric rolling, cryorolling, and asymmetric cryorolling. The asymmetric cryorolled samples exhibited a noteworthy ultra-fine-grain heterogeneous lamella structure. The microstructure and corresponding hardness obtained by different rolling processes and subsequent annealing are compared. It can be seen from the results that the cryogenic deformation temperature had a stronger effect on the mechanical properties of the medium entropy alloys (MEA), compared with the shear strain caused by the asymmetric cryorolling. The effect of annealing temperature on texture components and volume fractions of the specially rolled samples was also analyzed. The result revealed that the recrystallized MEA exhibited similar texture components and the corresponding volume fraction, which indicated that the rolling process had limited influence on the formation of annealing texture. The recrystallized texture after annealing retained the deformation texture and twin related orientations appeared. Asymmetric rolled MEA showed strong random composition than symmetric rolled MEA regardless of rolling temperature. The recrystallized textures of the species obtained by the three rolling processes did not exhibit a significant dependence on the annealing temperature. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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28 pages, 4551 KiB

Open AccessReview

Current Understanding of Bias-Temperature Instabilities in GaN MIS Transistors for Power Switching Applications

by Milan Ťapajna

Crystals 2020, 10(12), 1153; https://doi.org/10.3390/cryst10121153 - 18 Dec 2020

Cited by 18 | Viewed by 5515

Abstract

GaN-based high-electron mobility transistors (HEMTs) have brought unprecedented performance in terms of power, frequency, and efficiency. Application of metal-insulator-semiconductor (MIS) gate structure has enabled further development of these devices by improving the gate leakage characteristics, gate controllability, and stability, and offered several approaches [...] Read more.

GaN-based high-electron mobility transistors (HEMTs) have brought unprecedented performance in terms of power, frequency, and efficiency. Application of metal-insulator-semiconductor (MIS) gate structure has enabled further development of these devices by improving the gate leakage characteristics, gate controllability, and stability, and offered several approaches to achieve E-mode operation desired for switching devices. Yet, bias-temperature instabilities (BTI) in GaN MIS transistors represent one of the major concerns. This paper reviews BTI in D- and E-mode GaN MISHEMTs and fully recess-gate E-mode devices (MISFETs). Special attention is given to discussion of existing models describing the defects distribution in the GaN-based MIS gate structures as well as related trapping mechanisms responsible for threshold voltage instabilities. Selected technological approaches for improving the dielectric/III-N interfaces and techniques for BTI investigation in GaN MISHEMTs and MISFETs are also outlined. Full article

(This article belongs to the Special Issue Robust Microelectronic Devices)

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13 pages, 3378 KiB

Open AccessArticle

Properties of Barium Cerate Thin Films Formed Using E-Beam Deposition

by Monica Susana Campos Covarrubias, Mantas Sriubas, Kristina Bockute, Piotr Winiarz, Tadeusz Miruszewski, Wojciech Skubida, Daniel Jaworski, Michał Bartmański, Marek Szkodo, Maria Gazda and Giedrius Laukaitis

Crystals 2020, 10(12), 1152; https://doi.org/10.3390/cryst10121152 - 18 Dec 2020

Cited by 7 | Viewed by 2678

Abstract

This article focuses on the properties of the BaCeO₃ thin films formed by electron-beam vapor deposition and investigates the formation of barium cerates on supports with different thermal expansion coefficients (Stainless Steel, Invar, Glass Sealing, and Inconel substrates) and the influence of [...] Read more.

This article focuses on the properties of the BaCeO₃ thin films formed by electron-beam vapor deposition and investigates the formation of barium cerates on supports with different thermal expansion coefficients (Stainless Steel, Invar, Glass Sealing, and Inconel substrates) and the influence of the technological parameters on the properties of the formed thin films with an emphasis on the stability of the films. Morphology and phase composition and mechanical and electrical properties were investigated. It was found that the main factors influencing the phase composition and morphology of the films are the temperature of the support and the deposition rate. However, the mechanical properties of the films are mostly influenced by strains introduced to thin films by using different supports. Two interesting features of the electrical properties of the studied strained films were noticed: the film with the highest in-plane tensile strain showed the lowest activation energy of total conductivity, whereas the film with the lowest strain showed the highest value of total conductivity. Full article

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16 pages, 727 KiB

Open AccessReview

Cobalt–Chromium Dental Alloys: Metal Exposures, Toxicological Risks, CMR Classification, and EU Regulatory Framework

by Alina Vaicelyte, Christine Janssen, Marc Le Borgne and Brigitte Grosgogeat

Crystals 2020, 10(12), 1151; https://doi.org/10.3390/cryst10121151 - 18 Dec 2020

Cited by 55 | Viewed by 16365

Abstract

During the 20th century, metal alloys have assumed an important role as restorative materials. Among existing examples, cobalt–chromium (Co–Cr) alloys increasingly began to be used in medicine and especially in dentistry. Their success is mainly due to their mechanical properties such as stiffness, [...] Read more.

During the 20th century, metal alloys have assumed an important role as restorative materials. Among existing examples, cobalt–chromium (Co–Cr) alloys increasingly began to be used in medicine and especially in dentistry. Their success is mainly due to their mechanical properties such as stiffness, strength and corrosion resistance, thus allowing a high biocompatibility. There are quite meaningful data on the corrosion and toxicity of Co–Cr alloys for their use in restorative materials such as dental prostheses. Toxicological studies following Co and Cr exposures in the oral cavity are more difficult to conduct because there are many different situations leading to the release of metal ions and wear particles. Furthermore, the links between exposure and the appearance of local or systemic toxicity are not automatic. Since 2017, the European Union (EU) regulatory framework for Co–Cr alloys has been undergoing profound changes. A new EU Medical Devices Regulation (MDR) (2017/745) will be applied in May 2021 with the need to consider that Co metal is a new carcinogenic, mutagenic and toxic to reproduction (CMR) substance. On 18 February 2020, the 14th Adaptation to Technical Progress (ATP14) to the Classification, Labelling and Packaging (CLP) regulation was published, including the harmonised classification for Co metal as a CMR 1B substance. In this context, the use of Co might be forbidden if the medical devices are invasive and as soon as they include more than 0.1% (m/m) Co. This review provides a specific overview on Co–Cr dental alloys in terms of metal ions and wear particles release, toxicological risks, and the actual and new EU regulatory framework. Full article

(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)

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14 pages, 1341 KiB

Open AccessArticle

Detector Tilt Considerations in Bragg Coherent Diffraction Imaging: A Simulation Study

by Siddharth Maddali, Marc Allain, Peng Li, Virginie Chamard and Stephan O. Hruszkewycz

Crystals 2020, 10(12), 1150; https://doi.org/10.3390/cryst10121150 - 17 Dec 2020

Viewed by 2984

Abstract

This paper addresses the three-dimensional signal distortion and image reconstruction issues in X-ray Bragg coherent diffraction imaging (BCDI) in the event of a general non-orthogonal orientation of the area detector with respect to the diffracted beam. Growing interest in novel BCDI adaptations at [...] Read more.

This paper addresses the three-dimensional signal distortion and image reconstruction issues in X-ray Bragg coherent diffraction imaging (BCDI) in the event of a general non-orthogonal orientation of the area detector with respect to the diffracted beam. Growing interest in novel BCDI adaptations at fourth-generation synchrotron light sources has necessitated improvisations in the experimental configuration and the subsequent data analysis. One such possibly unavoidable improvisation that is envisioned in this paper is a photon-counting area detector whose face is tilted away from the perpendicular to the Bragg-diffracted beam during the acquisition of the coherent diffraction signal. We describe a likely circumstance in which one would require such a detector configuration, along with the experimental precedent at third-generation synchrotrons. Using physically accurate diffraction simulations from synthetic scatterers in the presence of such tilted detectors, we analyze the general nature of the observed signal distortion qualitatively and quantitatively and provide a prescription to correct for it during image reconstruction. Our simulations and reconstructions are based on an adaptation of the known theory of BCDI sampling geometry, as well as the recently developed projection-based methods of wavefield propagation. Such configurational modifications and their numerical remedies are potentially valuable in realizing unconventional coherent diffraction measurement geometries, eventually paving the way for the integration of BCDI into new material characterization experiments at next-generation light sources. Full article

(This article belongs to the Special Issue Coherent X-ray Scattering)

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22 pages, 18092 KiB

Open AccessArticle

5-Iodo-1-Arylpyrazoles as Potential Benchmarks for Investigating the Tuning of the Halogen Bonding

by Denisa Dumitrescu, Sergiu Shova, Isabela C. Man, Mino R. Caira, Marcel Mirel Popa and Florea Dumitrascu

Crystals 2020, 10(12), 1149; https://doi.org/10.3390/cryst10121149 - 17 Dec 2020

Cited by 14 | Viewed by 3319

Abstract

5-Iodo-1-arylpyrazoles are interesting templates for investigating the halogen bond propensity in small molecules other than the already well-known halogenated molecules such as tetrafluorodiiodobenzene. Herein, we present six compounds with different substitution on the aryl ring attached at position 1 of the pyrazoles and [...] Read more.

5-Iodo-1-arylpyrazoles are interesting templates for investigating the halogen bond propensity in small molecules other than the already well-known halogenated molecules such as tetrafluorodiiodobenzene. Herein, we present six compounds with different substitution on the aryl ring attached at position 1 of the pyrazoles and investigate them in the solid state in order to elucidate the halogen bonding significance to the crystallographic landscape of such molecules. The substituents on the aryl ring are generally combinations of halogen atoms (Br, Cl) and various alkyl groups. Observed halogen bonding types spanned by these six 5-iodopyrazoles included a wide variety, namely, C–I⋯O, C–I⋯π, C–I⋯Br, C–I⋯N and C–Br⋯O interactions. By single crystal X-ray diffraction analysis combined with the descriptive Hirshfeld analysis, we discuss the role and influence of the halogen bonds among the intermolecular interactions. Full article

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

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14 pages, 2032 KiB

Open AccessArticle

Discrimination of Aluminum from Silicon by Electron Crystallography with the JUNGFRAU Detector

by Erik Fröjdh, Julian T. C. Wennmacher, Przemyslaw Rzepka, Aldo Mozzanica, Sophie Redford, Bernd Schmitt, Jeroen A. van Bokhoven and Tim Gruene

Crystals 2020, 10(12), 1148; https://doi.org/10.3390/cryst10121148 - 17 Dec 2020

Cited by 8 | Viewed by 4122

Abstract

The crystal structure of a chemical compound serves several purposes: its coordinates represent three-dimensional information about the connectivity between the atoms; it is the only technique that determines the absolute configuration of chiral molecules; it enables determining structure–function relations; and crystallographic data at [...] Read more.

The crystal structure of a chemical compound serves several purposes: its coordinates represent three-dimensional information about the connectivity between the atoms; it is the only technique that determines the absolute configuration of chiral molecules; it enables determining structure–function relations; and crystallographic data at atomic resolution distinguish between element types and serve as a confirmation of synthesis protocols. Here, we collected electron diffraction data from albite and from a Linde Type A (LTA) type zeolite. Both compounds are aluminosilicates with well-defined silicon and aluminum crystallographic sites. Data were recorded with the “adJUstiNg Gain detector FoR the Aramis User station” (JUNGFRAU detector) and we made use of its capability of energy discrimination to suppress noise. For both compounds, crystallographic refinement distinguishes correctly between silicon and aluminum, even though these elements have very similar electron scattering factors. These results highlight the quality of the electron diffraction data and the reliability of the models for chemical interpretation. Further development in this direction will provide enormous opportunities for structure–function studies by diffraction. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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15 pages, 6955 KiB

Open AccessArticle

Influence of Trapped Gas on Pore Healing under Hot Isostatic Pressing in Nickel-Base Superalloys

by Mahesh R. G. Prasad, Siwen Gao, Napat Vajragupta and Alexander Hartmaier

Crystals 2020, 10(12), 1147; https://doi.org/10.3390/cryst10121147 - 17 Dec 2020

Cited by 15 | Viewed by 2830

Abstract

Under the typical hot isostatic pressing (HIP) processing conditions, plastic deformation by dislocation slip is considered the primary mechanism for pore shrinkage, according to experimental observations and deformation mechanism maps. In the present work, a crystal plasticity model has been used to investigate [...] Read more.

Under the typical hot isostatic pressing (HIP) processing conditions, plastic deformation by dislocation slip is considered the primary mechanism for pore shrinkage, according to experimental observations and deformation mechanism maps. In the present work, a crystal plasticity model has been used to investigate the influence of applied pressure and holding time on porosity reduction in a nickel-base single crystal superalloy. The influence of trapped gas on pore shrinkage is modeled by coupling mechanical deformation with pore–gas interaction. In qualitative agreement with experimental investigations, we observe that increasing the applied pressure or the holding time can effectively reduce porosity. Furthermore, the effect of pore shape on the shrinkage is observed to depend on a combination of elastic anisotropy and the complex distribution of stresses around the pore. Simulation results also reveal that, for pores of the same shape, smaller pores (radius < 0.1 μm) have a higher shrinkage rate in comparison to larger pores (radius ≥ 0.1 μm), which is attributed to the increasing pore surface energies with decreasing pore sizes. It is also found that, for smaller initial gas-filled pores (radius < 0.1 μm), HIP can result in very high gas pressures (on the order of GPa). Such high pressures either act as a driving force for argon to diffuse into the surrounding metal during HIP itself, or it can result in pore re-opening during subsequent annealing or mechanical loading. These results demonstrate that the micromechanical model can quantitatively evaluate the individual influences of HIP processing conditions and pore characteristics on pore annihilation, which can help optimize the HIP process parameters in the future. Full article

(This article belongs to the Special Issue Crystal Plasticity)

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8 pages, 1225 KiB

Open AccessCommunication

The Effect of a Weak Magnetic Field (0 T to 0.4 T) on the Valence Band and Intramolecular Hydrogen of Inorganic Aerosol Metal–Nitrogen Gas Chemical Reactions in a Sparking Discharge Process

by Stefan Ručman, Chatdanai Boonruang and Pisith Singjai

Crystals 2020, 10(12), 1141; https://doi.org/10.3390/cryst10121141 - 17 Dec 2020

Cited by 4 | Viewed by 3044

Abstract

The effects of a weak magnetic field on chemical reactions are still not well understood. In our research, we used a sparking discharge process to ionize and atomize different metal wires in ambient air under usual atmospheric conditions, with and without the presence [...] Read more.

The effects of a weak magnetic field on chemical reactions are still not well understood. In our research, we used a sparking discharge process to ionize and atomize different metal wires in ambient air under usual atmospheric conditions, with and without the presence of a magnetic field. Products were collected on a glass substrate and additionally characterized for the presence of nitrogen or nitride bonding with XPS. All samples sparked with no magnetic field provided an evidence of nitride formation. Additional characterization and comparison of samples prepared inside and outside a magnetic field was performed using FTIR and collected in deionized (DI) water to investigate the influence on conductivity and pH. When the magnetic field was present during sparking discharge, a higher concentration of nanoparticles was produced. Full article

(This article belongs to the Special Issue Magnetіc Structure Compounds)

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13 pages, 3962 KiB

Open AccessArticle

Kilohertz Macromolecular Crystallography Using an EIGER Detector at Low X-ray Fluxes

by Krishna P. Khakurel, Shirly Espinoza, Martin Savko, Vitaly Polovinkin, Jan Dohnalek, William Shepard, Angelina Angelova, Janos Hajdu, Jakob Andreasson and Borislav Angelov

Crystals 2020, 10(12), 1146; https://doi.org/10.3390/cryst10121146 - 16 Dec 2020

Cited by 3 | Viewed by 3795

Abstract

Time-resolved in-house macromolecular crystallography is primarily limited by the capabilities of the in-house X-ray sources. These sources can only provide a time-averaged structure of the macromolecules. A significant effort has been made in the development of in-house laser-driven ultrafast X-ray sources, with one [...] Read more.

Time-resolved in-house macromolecular crystallography is primarily limited by the capabilities of the in-house X-ray sources. These sources can only provide a time-averaged structure of the macromolecules. A significant effort has been made in the development of in-house laser-driven ultrafast X-ray sources, with one of the goals as realizing the visualization of the structural dynamics of macromolecules at a very short timescale within the laboratory-scale infrastructure. Most of such in-house ultrafast X-ray sources are operated at high repetition rates and usually deliver very low flux. Therefore, the necessity of a detector that can operate at the repetition rate of the laser and perform extremely well under low flux conditions is essential. Here, we present experimental results demonstrating the usability of the hybrid-pixel detectors, such as Eiger X 1M, and provide experimental proof that they can be successfully operated to collect macromolecular crystallographic data up to a detector frame rate of 3 kHz from synchrotron sources. Our results also show that the data reduction and structural analysis are successful at such high frame rates and fluxes as low as 10⁸ photons/s, which is comparable to the values expected from a typical laser-driven X-ray source. Full article

(This article belongs to the Special Issue Time-Resolved X-ray Diffraction and Scattering Techniques Applied to Dynamical Processes)

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12 pages, 1556 KiB

Open AccessEditor’s ChoiceArticle

Shock Damage Analysis in Serial Femtosecond Crystallography Data Collected at MHz X-ray Free-Electron Lasers

by Alexander Gorel, Marie Luise Grünbein, Richard Bean, Johan Bielecki, Mario Hilpert, Michele Cascella, Jacques-Philippe Colletier, Hans Fangohr, Lutz Foucar, Elisabeth Hartmann, Mark S. Hunter, Henry Kirkwood, Marco Kloos, Romain Letrun, Thomas Michelat, Robert L. Shoeman, Jolanta Sztuk-Dambietz, Guillaume Tetreau, Herbert Zimmermann, Adrian P. Mancuso, Thomas R.M. Barends, R. Bruce Doak, Claudiu Andrei Stan and Ilme Schlichting Show full author list Hide full author list

Crystals 2020, 10(12), 1145; https://doi.org/10.3390/cryst10121145 - 16 Dec 2020

Cited by 5 | Viewed by 3675

Abstract

Serial femtosecond crystallography (SFX) data were recorded at the European X-ray free-electron laser facility (EuXFEL) with protein microcrystals delivered via a microscopic liquid jet. An XFEL beam striking such a jet may launch supersonic shock waves up the jet, compromising the oncoming sample. [...] Read more.

Serial femtosecond crystallography (SFX) data were recorded at the European X-ray free-electron laser facility (EuXFEL) with protein microcrystals delivered via a microscopic liquid jet. An XFEL beam striking such a jet may launch supersonic shock waves up the jet, compromising the oncoming sample. To investigate this efficiently, we employed a novel XFEL pulse pattern to nominally expose the sample to between zero and four shock waves before being probed. Analyzing hit rate, indexing rate, and resolution for diffraction data recorded at MHz pulse rates, we found no evidence of damage. Notably, however, this conclusion could only be drawn after careful identification and assimilation of numerous interrelated experimental factors, which we describe in detail. Failure to do so would have led to an erroneous conclusion. Femtosecond photography of the sample-carrying jet revealed critically different jet behavior from that of all homogeneous liquid jets studied to date in this manner. Full article

(This article belongs to the Special Issue Approach of Serial Crystallography)

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18 pages, 21908 KiB

Open AccessEditor’s ChoiceArticle

Dynamics of Quasiperiodic Beams

by Mohit Gupta and Massimo Ruzzene

Crystals 2020, 10(12), 1144; https://doi.org/10.3390/cryst10121144 - 16 Dec 2020

Cited by 16 | Viewed by 3979

Abstract

Quasiperiodic metastrucures are characterized by edge localized modes of topological nature, which can be of significant technological interest. We here investigate such topological modes for stiffened and sandwich beams, which can be employed as structural members with inherent vibration localization capabilities. Quasiperiodicity is [...] Read more.

Quasiperiodic metastrucures are characterized by edge localized modes of topological nature, which can be of significant technological interest. We here investigate such topological modes for stiffened and sandwich beams, which can be employed as structural members with inherent vibration localization capabilities. Quasiperiodicity is achieved by altering the geometric properties and material properties of the beams. Specifically, in the stiffened beams, the geometric location of stiffeners is modulated to quasiperiodic patterns, while, in the sandwich beams, the core’s material properties are varied in a step-wise manner to generate such patterns. The families of periodic and quasiperiodic beams for both stiffened and sandwich-type are obtained by varying a projection parameter that governs the location of the center of the stiffener or the alternating core, respectively. The dynamics of stiffened quasiperiodic beams is investigated through 3-D finite element simulations, which leads to the observation of the fractal nature of the bulk spectrum and the illustration of topological edge modes that populate bulk spectral bandgaps. The frequency spectrum is further elucidated by employing polarization factors that distinguish multiple contributing modes. The frequency response of the finite stiffened cantilever beams confirms the presence of modes in the non-trivial bandgaps and further demonstrates that those modes are localized at the free edge. A similar analysis is conducted for the analysis of sandwich composite beams, for which computations rely on a dynamic stiffness matrix approach. This work motivates the use of quasiperiodic beams in the design of stiffened and sandwich structures as structural members in applications where vibration isolation is combined with load-carrying functions. Full article

(This article belongs to the Special Issue Emerging Trends in Phononic Crystals)

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14 pages, 1323 KiB

Open AccessArticle

The Impact of Interfacial Charge Trapping on the Reproducibility of Measurements of Silicon Carbide MOSFET Device Parameters

by Maximilian W. Feil, Andreas Huerner, Katja Puschkarsky, Christian Schleich, Thomas Aichinger, Wolfgang Gustin, Hans Reisinger and Tibor Grasser

Crystals 2020, 10(12), 1143; https://doi.org/10.3390/cryst10121143 - 16 Dec 2020

Cited by 13 | Viewed by 3642

Abstract

Silicon carbide is an emerging material in the field of wide band gap semiconductor devices. Due to its high critical breakdown field and high thermal conductance, silicon carbide MOSFET devices are predestined for high-power applications. The concentration of defects with short capture and [...] Read more.

Silicon carbide is an emerging material in the field of wide band gap semiconductor devices. Due to its high critical breakdown field and high thermal conductance, silicon carbide MOSFET devices are predestined for high-power applications. The concentration of defects with short capture and emission time constants is higher than in silicon technologies by orders of magnitude which introduces threshold voltage dynamics in the volt regime even on very short time scales. Measurements are heavily affected by timing of readouts and the applied gate voltage before and during the measurement. As a consequence, device parameter determination is not as reproducible as in the case of silicon technologies. Consequent challenges for engineers and researchers to measure device parameters have to be evaluated. In this study, we show how the threshold voltage of planar and trench silicon carbide MOSFET devices of several manufacturers react on short gate pulses of different lengths and voltages and how they influence the outcome of application-relevant pulsed current-voltage characteristics. Measurements are performed via a feedback loop allowing in-situ tracking of the threshold voltage with a measurement delay time of only 1

μ s

. Device preconditioning, recently suggested to enable reproducible BTI measurements, is investigated in the context of device parameter determination by varying the voltage and the length of the preconditioning pulse. Full article

(This article belongs to the Special Issue Robust Microelectronic Devices)

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13 pages, 2023 KiB

Open AccessArticle

Femtosecond Laser-Induced Self-Assembly of Ce³⁺-Doped YAG Nanocrystals

by Yasuhiko Shimotsuma, Kotaro Tomura, Tatsuya Okuno, Masahiro Shimizu and Kiyotaka Miura

Crystals 2020, 10(12), 1142; https://doi.org/10.3390/cryst10121142 - 16 Dec 2020

Cited by 7 | Viewed by 2848

Abstract

Direct three-dimensional laser writing of crystallization inside glass has been intensely studied as an attractive technique for fabricating photonic devices. In particular, polarization-dependent periodic nanostructures composed of the partial crystallization in glass can be self-assembled through focused irradiation of femtosecond pulses. Here, we [...] Read more.

Direct three-dimensional laser writing of crystallization inside glass has been intensely studied as an attractive technique for fabricating photonic devices. In particular, polarization-dependent periodic nanostructures composed of the partial crystallization in glass can be self-assembled through focused irradiation of femtosecond pulses. Here, we report on the Y₃Al₅O₁₂ (YAG) crystal precipitation in nanoscale by femtosecond laser irradiation inside Al₂O₃-Y₂O₃ glass. Furthermore, we focus on the white emission by Ce: YAG in which a part of Y³⁺ site was replaced by Ce³⁺, the effect on photoluminescence (PL) characteristics by changing of ligand field induced by nanostructure formation was observed. Full article

(This article belongs to the Special Issue Laser-Induced Crystallization)

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22 pages, 8300 KiB

Open AccessArticle

Restoration Mechanisms at Moderate Temperatures for As-Cast ZK40 Magnesium Alloys Modified with Individual Ca and Gd Additions

by Ricardo Henrique Buzolin, Leandro Henrique Moreno Guimaraes, Julián Arnaldo Ávila Díaz, Erenilton Pereira da Silva, Domonkos Tolnai, Chamini L. Mendis, Norbert Hort and Haroldo Cavalcanti Pinto

Crystals 2020, 10(12), 1140; https://doi.org/10.3390/cryst10121140 - 16 Dec 2020

Cited by 1 | Viewed by 2704

Abstract

The deformation behaviour of as-cast ZK40 alloys modified with individual additions of Ca and Gd is investigated at 250 °C and 300 °C. Compression tests were carried out at 0.0001 s⁻¹ and 0.001 s⁻¹ using a modified Gleeble system during in-situ [...] Read more.

The deformation behaviour of as-cast ZK40 alloys modified with individual additions of Ca and Gd is investigated at 250 °C and 300 °C. Compression tests were carried out at 0.0001 s⁻¹ and 0.001 s⁻¹ using a modified Gleeble system during in-situ synchrotron radiation diffraction experiments. The deformation mechanisms are corroborated by post-mortem investigations using scanning electron microscopy combined with electron backscattered diffraction measurements. The restoration mechanisms in α-Mg are listed as follows: the formation of misorientation spread within α-Mg, the formation of low angle grain boundaries via dynamic recovery, twinning, as well as dynamic recrystallisation. The Gd and Ca additions increase the flow stress of the ZK40, which is more evident at 0.001 s⁻¹ and 300 °C. Dynamic recovery is the predominant restoration mechanism in all alloys. Continuous dynamic recrystallisation only occurs in the ZK40 at 250 °C, competing with discontinuous dynamic recrystallisation. Discontinuous dynamic recrystallisation occurs for the ZK40 and ZK40-Gd. The Ca addition hinders discontinuous dynamic recrystallisation for the investigated temperatures and up to the local achieved strain. Gd addition forms a semi-continuous network of intermetallic compounds along the grain boundaries that withstand the load until their fragmentation, retarding discontinuous dynamic recrystallisation. Full article

(This article belongs to the Special Issue Processing and Characterization of Magnesium-Based Materials)

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10 pages, 2817 KiB

Open AccessArticle

Synergistic Effect of MWCNT and Carbon Fiber Hybrid Fillers on Electrical and Mechanical Properties of Alkali-Activated Slag Composites

by Hyeong Min Park, Chanho Park, Jinho Bang, Minwook Lee and Beomjoo Yang

Crystals 2020, 10(12), 1139; https://doi.org/10.3390/cryst10121139 - 15 Dec 2020

Cited by 12 | Viewed by 2568 | Correction

Abstract

Herein, we investigated the synergistic effect of multi-walled carbon nanotube (MWCNT) and carbon fiber (CF) hybrid fillers on electrical and mechanical characteristics of alkali-activated slag (AAS) composites. Many studies on AAS composites have been conducted in the past; however, not much progress has [...] Read more.

Herein, we investigated the synergistic effect of multi-walled carbon nanotube (MWCNT) and carbon fiber (CF) hybrid fillers on electrical and mechanical characteristics of alkali-activated slag (AAS) composites. Many studies on AAS composites have been conducted in the past; however, not much progress has been made regarding characteristics of AAS composites with hybrid conductive fillers. The specimens with different mix proportions were fabricated in the present study, and numerous material characteristics, including flowability, electrical resistivity, and compressive strength of AAS composites were measured. In addition, the synergistic effects were investigated through scanning electron microscopy and thermogravimetric analysis. It was found that the 0.5 wt.% of MWCNTs and CFs lead the effects of the bridging and reducing crack propagation, thereby improving its electrical and mechanical performances. The filler exceeding a percolation point improved the electrical performance of the AAS composites; however, it interfered with the hydration process during the curing period, and caused a decrease in compressive strength of AAS composites. Full article

(This article belongs to the Special Issue Carbon Nano-Composite Materials)

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11 pages, 2435 KiB

Open AccessArticle

Microstructural and Hardness Evolution in a Duplex Stainless Steel Processed by High-Pressure Torsion

by Ming Ma, Hua Ding, Yi Huang, Cheng Wei Tian and Terence G. Langdon

Crystals 2020, 10(12), 1138; https://doi.org/10.3390/cryst10121138 - 15 Dec 2020

Cited by 6 | Viewed by 2366

Abstract

The duplex stainless steel 2205, designated DSS2205 and having a duplex structure comprising ferrite and austenite phases, was processed by high-pressure torsion (HPT) and the microstructural and hardness evolutions were investigated after various HPT revolutions and at different positions within the specimens. The [...] Read more.

The duplex stainless steel 2205, designated DSS2205 and having a duplex structure comprising ferrite and austenite phases, was processed by high-pressure torsion (HPT) and the microstructural and hardness evolutions were investigated after various HPT revolutions and at different positions within the specimens. The results show that the grain refinement induced by severe deformation processing is different in the ferrite and austenite phases such that the ferrite grains are refined via dislocation subdivision, whereas grain refinement in the austenite phase depends mainly on the interaction of dislocations and twin boundaries at relatively low strains. When the numbers of revolutions increases, the grain refinement in austenite restricts the occurrence of deformation twinning so that dislocation slip becomes dominant. During HPT processing, the effect of the phase boundaries on the mechanical properties of the alloy is very significant. The results show the average width between two adjacent phases and the hardness of the alloy are generally consistent with the classical Hall–Petch relationship. Full article

(This article belongs to the Special Issue Study of Structure, Heat Treatment and Properties of Steels)

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10 pages, 3220 KiB

Open AccessCommunication

Enhancement of Crystallization Behaviors in Quaternary Composites Containing Biodegradable Polymer by Supramolecular Inclusion Complex

by Li-Ting Lee, Sheng-Ping He and Chih-Feng Huang

Crystals 2020, 10(12), 1137; https://doi.org/10.3390/cryst10121137 - 12 Dec 2020

Cited by 3 | Viewed by 2085

Abstract

Novel multi-component composites composed of the biodegradable polymer poly(ethylene adipate) (PEA), the water-soluble polymer poly(ethylene oxide) (PEO), poly(vinyl acetate) (PVAc), and a supramolecular-like inclusion complex (IC) made by α-cyclodextrin (α-CD) and poly(ε-caprolactone) (PCL) (coded as PCL–CD–IC) are discussed in this work. The PCL–CD–IC [...] Read more.

Novel multi-component composites composed of the biodegradable polymer poly(ethylene adipate) (PEA), the water-soluble polymer poly(ethylene oxide) (PEO), poly(vinyl acetate) (PVAc), and a supramolecular-like inclusion complex (IC) made by α-cyclodextrin (α-CD) and poly(ε-caprolactone) (PCL) (coded as PCL–CD–IC) are discussed in this work. The PCL–CD–IC was used to increase the crystallization rate of the miscible PEA/PEO/PVAc ternary blend that crystalized slower than neat PEA. Higher resolution SEM and TEM images displayed that PCL–CD–IC did not assemble notably in the quaternary composites. For the results of isothermal crystallization, the analysis of the Avrami equation demonstrated that the rate constant k increased with the addition of PCL–CD–IC in the composites, suggesting that PCL–CD–IC provided more nucleation sites to promote the crystallization rate. The nucleation density increased with the addition of PCL–CD–IC, and the amount of spherulite also increased. Wide angle X-ray results showed that the composites displayed similar diffraction patterns to neat PEA, meaning PEO, PVAc, and PCL–CD–IC would not change the crystal structures of PEA in the composites. The PCL–CD–IC, the supramolecular nucleation agent, demonstrated its superior ability to enhance the multi-component composites of biodegradable polymer in this study. Full article

(This article belongs to the Special Issue Feature Papers in Macromolecular Crystals)

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11 pages, 2552 KiB

Open AccessArticle

Crystal Structure and Spectroscopic Analysis of the Compatible Solute Nγ-Acetyl-L-2,4-Diaminobutyric Acid

by Lea Martin, Wilhelm Klein, Sebastian P. Schwaminger, Thomas F. Fässler and Sonja Berensmeier

Crystals 2020, 10(12), 1136; https://doi.org/10.3390/cryst10121136 - 12 Dec 2020

Cited by 1 | Viewed by 2925

Abstract

Compatible solutes are low molecular weight, highly water-soluble and neutrally net-charged molecules with various protective functionalities that accumulate and are produced in microorganisms. Their multi-purpose functionalities, also adaptable in vitro, make them potential components in healthcare and cosmetic products. One promising but insufficiently [...] Read more.

Compatible solutes are low molecular weight, highly water-soluble and neutrally net-charged molecules with various protective functionalities that accumulate and are produced in microorganisms. Their multi-purpose functionalities, also adaptable in vitro, make them potential components in healthcare and cosmetic products. One promising but insufficiently examined representative of this molecule class is Nγ-acetyl-L-2,4-diaminobutyric acid (γ-NADA), the metabolic precursor of ectoine. Here, we demonstrate the crystallization ability of γ-NADA by using cooling crystallization in aqueous solvents and find that it forms rod-shaped crystals. According to a single crystal structure determination, γ-NADA is orthorhombic with space group P2₁2₁2₁ and a = 5.3647(1), b = 8.3652(2), c = 16.9149(5) Å, Z = 4, R₁ = 3.48%, wR₂ = 7.33% (all data). Additionally, γ-NADA is analyzed via Raman, IR, ¹H, and ¹³C NMR spectroscopy. Full article

(This article belongs to the Section Biomolecular Crystals)

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