Crystals

14 pages, 4604 KiB

Open AccessArticle

Carbon Nanodots as a Potential Transport Layer for Boosting Performance of All-Inorganic Perovskite Nanocrystals-Based Photodetector

by Hassan Algadi, Ahmad Umar, Hasan Albargi, Turki Alsuwian and Sotirios Baskoutas

Crystals 2021, 11(6), 717; https://doi.org/10.3390/cryst11060717 - 21 Jun 2021

Cited by 14 | Viewed by 3408

Abstract

A low-cost and simple drop-casting method was used to fabricate a carbon nanodot (C-dot)/all-inorganic perovskite (CsPbBr₃) nanosheet bilayer heterojunction photodetector on a SiO₂/Si substrate. The C-dot/perovskite bilayer heterojunction photodetector shows a high performance with a responsivity (R) of 1.09 [...] Read more.

A low-cost and simple drop-casting method was used to fabricate a carbon nanodot (C-dot)/all-inorganic perovskite (CsPbBr₃) nanosheet bilayer heterojunction photodetector on a SiO₂/Si substrate. The C-dot/perovskite bilayer heterojunction photodetector shows a high performance with a responsivity (R) of 1.09 A/W, almost five times higher than that of a CsPbBr₃-based photodetector (0.21 A/W). In addition, the hybrid photodetector exhibits a fast response speed of 1.318/1.342 µs and a highly stable photocurrent of 6.97 µA at 10 V bias voltage. These figures of merits are comparable with, or much better than, most reported perovskite heterojunction photodetectors. UV–Vis absorption and photoluminescent spectra measurements reveal that the C-dot/perovskite bilayer heterojunction has a band gap similar to the pure perovskite layer, confirming that the absorption and emission in the bilayer heterojunction is dominated by the top layer of the perovskite. Moreover, the emission intensity of the C-dot/perovskite bilayer heterojunction is less than that of the pure perovskite layer, indicating that a significant number of charges were extracted by the C-dot layer. The studied band alignment of the C-dots and perovskites in the dark and under emission reveals that the photodetector has a highly efficient charge separation mechanism at the C-dot/perovskite interface, where the recombination rate between photogenerated electrons and holes is significantly reduced. This highly efficient charge separation mechanism is the main reason behind the enhanced performance of the C-dot/perovskite bilayer heterojunction photodetector. Full article

(This article belongs to the Special Issue Functional Nanomaterials for Advanced Applications)

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16 pages, 4068 KiB

Open AccessArticle

Band-Gap Properties of Finite Locally Resonant Beam Suspended Periodically with Two-Degree-of-Freedom Force Type Resonators

by Hangyuan Lv, Shangjie Li, Xianzhen Huang and Zhongliang Yu

Crystals 2021, 11(6), 716; https://doi.org/10.3390/cryst11060716 - 21 Jun 2021

Cited by 7 | Viewed by 2397

Abstract

The propagation properties of waves in finite Timoshenko locally resonant (LR) beams resting on forced vibrations and periodically attached two-degree-of-freedom force-type resonators are studied by the wave-based analysis approach. By calculating the motion equations of the beam, the transmission and reflection matrices of [...] Read more.

The propagation properties of waves in finite Timoshenko locally resonant (LR) beams resting on forced vibrations and periodically attached two-degree-of-freedom force-type resonators are studied by the wave-based analysis approach. By calculating the motion equations of the beam, the transmission and reflection matrices of waves at the resonator attached point are first derived, and the forced vibration response of the finite periodic beam is deduced by the wave-based approach. Several examples are also analyzed by the finite element method to verify the high accuracy of the developed wave-based analysis approach. Numerical results show that wider low-frequency band-gaps exist in this type of LR beams. It was also found that the resonator masses and spring stiffnesses caused different effects on the band-gap properties of the combined LR beam. The desired band-gap widths of the LR beam can be tuned by adjusting the mass blocks and spring stiffness in the resonators based on the results. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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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 23 | Viewed by 4018

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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17 pages, 5330 KiB

Open AccessArticle

Simultaneous Hydrolysis and Detection of Organophosphate by Benzimidazole Containing Ligand-Based Zinc(II) Complexes

by Gaber A. M. Mersal, Hamdy S. El-Sheshtawy, Mohammed A. Amin, Nasser Y. Mostafa, Amine Mezni, Sarah Alharthi, Rabah Boukherroub and Mohamed M. Ibrahim

Crystals 2021, 11(6), 714; https://doi.org/10.3390/cryst11060714 - 21 Jun 2021

Cited by 6 | Viewed by 2334

Abstract

The agricultural use of organophosphorus pesticides is a widespread practice with significant advantages in crop health and product yield. An undesirable consequence is the contamination of soil and groundwater by these neurotoxins resulting from over application and run-off. Here, we design and synthesize [...] Read more.

The agricultural use of organophosphorus pesticides is a widespread practice with significant advantages in crop health and product yield. An undesirable consequence is the contamination of soil and groundwater by these neurotoxins resulting from over application and run-off. Here, we design and synthesize the mononuclear zinc(II) complexes, namely, [Zn(AMB)₂Cl](ClO₄) 1 and [Zn(AMB)₂(OH)](ClO₄) 2 (AMB = 2-aminomethylbenzimidazole), as artificial catalysts inspired by phosphotriesterase (PTE) for the hydrolysis of organophosphorus compounds (OPs) and simultaneously detect the organophosphate pesticides such as fenitrothion and parathion. Spectral and DFT (B3LYP/Lanl2DZ) calculations revealed that complexes 1 and 2 have a square-pyramidal environment around zinc(II) centers with coordination chromophores of ZnN₄Cl and ZnN₄O, respectively. Both 1 and 2 were used as a modifier in the construction of a biomimetic sensor for the determination of toxic OPs, fenitrothion and parathion, in phosphate buffer by square wave voltammetry. The hydrolysis of OPs using 1 or 2 generates p-nitrophenol, which is subsequently oxidized at the surface of the modified carbon past electrode. The catalytic activity of 2 was higher than 1, which is attributed to the higher electronegativity of the former. The oxidation peak potentials of p-nitrophenol were obtained at +0.97 V (vs. Ag/AgCl) using cyclic voltammetry (CV) and +0.88 V (vs. Ag/AgCl) using square wave voltammetry. Several parameters were investigated to evaluate the performance of the biomimetic sensor obtained after the incorporation of zinc(II) complex 1 and 2 on a carbon paste electrode (CPE). The calibration curve showed a linear response ranging between 1.0 μM (0.29 ppm) and 5.5 μM (1.6 ppm) for fenitrothion and 1.0 μM (0.28 ppm) and 0.1 μM (0.028 ppm) for parathion with a limit of detection (LOD) of 0.08 μM (0.022 ppm) and 0.51 μM (0.149 ppm) for fenitrothion and parathion, respectively. The obtained results clearly demonstrated that the CPE modified by 1 and 2 has a remarkable electrocatalytic activity towards the hydrolysis of OPs under optimal conditions. Full article

(This article belongs to the Special Issue Research about Vital Organic Chelates and Metal Ion Complexes)

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13 pages, 10394 KiB

Open AccessArticle

Quasi-Continuous Production and Separation of Lysozyme Crystals on an Integrated Laboratory Plant

by Timo Dobler, Benjamin Radel, Marco Gleiss and Hermann Nirschl

Crystals 2021, 11(6), 713; https://doi.org/10.3390/cryst11060713 - 21 Jun 2021

Cited by 7 | Viewed by 2471

Abstract

Vacuum crystallization with subsequent solid–liquid separation is a suitable method to produce and separate the temperature-sensitive protein lysozyme. The conventional process is performed batch-wise and on different devices, which in turn leads to disadvantages in terms of energy efficiency, contamination risk and process [...] Read more.

Vacuum crystallization with subsequent solid–liquid separation is a suitable method to produce and separate the temperature-sensitive protein lysozyme. The conventional process is performed batch-wise and on different devices, which in turn leads to disadvantages in terms of energy efficiency, contamination risk and process control. This publication therefore focuses on the application of the previously multistage process to a quasi-continuous, integrated single plant. The transfer occurs successively and starts with the substitution of the batch vessel by a process chamber. Afterwards, the filtration scale is increased and the formerly deployed membrane is replaced by an industrial filter cloth. Based on the results of these experiments, the complete process chain is successfully transferred to an integrated laboratory plant. Full article

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

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22 pages, 31042 KiB

Open AccessArticle

Conductivity Transitions of La_0.7Sr_0.3MnO_3±δ and La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ in Ce_0.9Gd_0.1O_2−δ Matrix for Dual-Phase Oxygen Transport Membranes

by Thuy Linh Pham, Ji Haeng Yu and Jong-Sook Lee

Crystals 2021, 11(6), 712; https://doi.org/10.3390/cryst11060712 - 21 Jun 2021

Cited by 3 | Viewed by 2423

Abstract

Using van der Pauw method, the conductivity of disk samples of

{La}_{0.7} {Sr}_{0.3} {MnO}_{3 \pm δ}

(LSM) and

{La}_{0.6} {Sr}_{0.4} {Co}_{0.2} {Fe}_{0.8} O_{3 - δ}

(LSCF) in a [...] Read more.

Using van der Pauw method, the conductivity of disk samples of

{La}_{0.7} {Sr}_{0.3} {MnO}_{3 \pm δ}

(LSM) and

{La}_{0.6} {Sr}_{0.4} {Co}_{0.2} {Fe}_{0.8} O_{3 - δ}

(LSCF) in a

{Ce}_{0.9} {Gd}_{0.1} O_{2 - δ}

(GDC) matrix was accurately quasi-continuously measured over 800 °C to −73 °C, and the transition points in Arrhenius behavior were systematically obtained from the extremum points of the second derivatives. While LSM-containing samples showed reproducible conductivity trajectories, the LSCF system exhibited unsystematic changes which may be related to the substantial oxidation/reduction reactions accompanying the ferroelastic–paraelastic transitions with a substantial thermal hysteresis at 650 °C to 750 °C, corresponding to conductivity maxima. A sudden decrease in activation energies on cooling corresponds to the para-to-ferromagnetic, weak insulator–metal transitions and the Curie temperature of LSM appears to gradually decrease in composites to 90 °C, while LSCF composites exhibit blurred transitions at approximately

- 40

°C. Relatively insulating paramagnetic phases are characterized by activation energy values ~0.2 eV, change to the high temperature phase exhibiting activation energy 0.1 eV for small polaron hopping mechanisms at 300 °C to 500 °C with increasing GDC content in the LSM composites and by two transitions at

\sim 60

°C and

\sim 245

°C for the LSCF composites. LSCF single phase shows distinctly lower transition points which appear to match with the singularly large c lattice parameter whereas the composites exhibit decreasing c with LSCF amount together with increasing lattice parameter of GDC. Van der Pauw conductivity is a feasible and sensitive in situ tool for monitoring the status of oxygen transport membranes. Full article

(This article belongs to the Special Issue Highly-Conductive Ceramics with Multiple Types of Mobile Charge Carriers)

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10 pages, 3060 KiB

Open AccessArticle

Hydrogen Molecules Rotational Stimulated Raman Scattering in All-Fiber Cavity Based on Hollow-Core Photonic Crystal Fibers

by Wenxi Pei, Hao Li, Wei Huang, Meng Wang and Zefeng Wang

Crystals 2021, 11(6), 711; https://doi.org/10.3390/cryst11060711 - 21 Jun 2021

Cited by 3 | Viewed by 2281

Abstract

Here, we report the rotational stimulated Raman scattering (SRS) of hydrogen molecules in an all-fiber cavity based on hollow-core photonic crystal fibers (HC-PCFs). The gas cavity consists of a 49 m long HC-PCF filled with 18 bar high-pressure hydrogen and two sections of [...] Read more.

Here, we report the rotational stimulated Raman scattering (SRS) of hydrogen molecules in an all-fiber cavity based on hollow-core photonic crystal fibers (HC-PCFs). The gas cavity consists of a 49 m long HC-PCF filled with 18 bar high-pressure hydrogen and two sections of fusion spliced solid-core fibers on both ends. When pumped by a homemade 1064 nm pulsed fiber amplifier, only rotational SRS occurs in the gas cavity due to the transmission spectral characteristics of the used HC-PCF, and 1135 nm Stokes wave is obtained (Raman frequency shift of 587 cm⁻¹). By changing the pulse width and repetition frequency of the pump source, the output characteristics are explored. In addition, a theoretical model is established for comparison with the experimental results. This work is helpful for the application of gas Raman laser based on the HC-PCFs. Full article

(This article belongs to the Special Issue Specialty Photonic Crystal Fibres and Their Applications)

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34 pages, 12339 KiB

Open AccessReview

Waste Glass Utilization in Cement-Based Materials for Sustainable Construction: A Review

by Di Qin, Yidan Hu and Xuemei Li

Crystals 2021, 11(6), 710; https://doi.org/10.3390/cryst11060710 - 21 Jun 2021

Cited by 34 | Viewed by 5270

Abstract

The construction industry has a significant environmental impact, contributing considerably to CO₂ emissions, natural resource depletion, and energy consumption. The construction industry is currently trending towards using alternative construction materials in place of natural materials and cement, thereby reducing the environmental impact [...] Read more.

The construction industry has a significant environmental impact, contributing considerably to CO₂ emissions, natural resource depletion, and energy consumption. The construction industry is currently trending towards using alternative construction materials in place of natural materials and cement, thereby reducing the environmental impact and promoting sustainability. Two approaches have been used in this review: scientometric analysis and a comprehensive manual review on the waste glass (WG) utilization in cement-based materials (CBMs) as a sustainable approach. Scientometric analysis is conducted to find out the current research trend from available bibliometric data and to identify the relevant publication fields, sources with the most publications, the most frequently used keywords, the most cited articles and authors, and the countries that have made the most significant contribution to the field of WG utilization in CBMs. The effect of WG on the mechanical properties of CBMs was found to be inconsistent in the literature. The inconsistent effects of WG impede its acceptance in the construction sector. This study intends to shed light on the arguments and tries to explain the opposing perspectives. This article summarizes the findings of various research groups and recommends new viewpoints based on the assessment of fundamental processes. The effect of utilizing WG on fresh and hardened properties of CBMs, including workability, compressive strength, split-tensile strength, and flexural strength, are reviewed. Furthermore, the microstructure and durability of composites containing WG are investigated. Different limitations associated with WG use in CBMs and their possible solution are reported. This study will assist researchers in identifying gaps in the present research. Additionally, the scientometric review will enable researchers from diverse regions to exchange novel ideas and technologies, collaborate on research, and form joint ventures. Full article

(This article belongs to the Special Issue Properties and Performance of Concrete Materials and Structures)

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16 pages, 12124 KiB

Open AccessArticle

The Effect of Nickel Contents on the Microstructure Evolution and Toughness of 800 MPa Grade Low Carbon Bainite Deposited Metal

by Jingwu Liu, Jian Sun, Shitong Wei and Shanping Lu

Crystals 2021, 11(6), 709; https://doi.org/10.3390/cryst11060709 - 21 Jun 2021

Cited by 13 | Viewed by 2504

Abstract

In this work, three deposited metals with different nickel (Ni) contents were produced by active gas metal arc welding (GMAW) in order to explore the influence of Ni on the microstructure evolution and toughness of 800 MPa grade low carbon bainite deposited metal. [...] Read more.

In this work, three deposited metals with different nickel (Ni) contents were produced by active gas metal arc welding (GMAW) in order to explore the influence of Ni on the microstructure evolution and toughness of 800 MPa grade low carbon bainite deposited metal. The results showed that microstructure of the deposited metals mainly consisted of lath bainite, lath martensite, coalesced bainite (CB), and retained austenite (RA), and that the toughness was closely related to two factors: CB and RA. RA in deposited metal could improve the toughness, while the CB would deteriorate the toughness of deposited metal. As the Ni content increased, a large amount of CB was generated in the deposited metals. The RA content increased from 1.5% to 5.7% with the content of Ni increasing from 5.5% to 6.5%. However, the RA content did not increase when the Ni content increased from 6.5% to 7.5%. Additionally, the smallest control unit of toughness in 800 MPa grade low carbon bainite deposited metals is the Bain Packet (BP) from the perspective of crystallography characteristics. This work provided a reference for the chemical composition design of 800 MPa grade steel welding consumables and showed that the toughness of the deposited metal could be improved effectively by increasing the RA content while suppressing the formation of CB. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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13 pages, 3475 KiB

Open AccessArticle

Interactions between Cationic Dye Toluidine Blue and Fibrous Clay Minerals

by Qingfeng Wu, Kristen Carlson, Qi Cheng, Xisen Wang and Zhaohui Li

Crystals 2021, 11(6), 708; https://doi.org/10.3390/cryst11060708 - 20 Jun 2021

Cited by 7 | Viewed by 2590

Abstract

Interactions between cationic dyes and negatively charged mineral surfaces have long attracted great attention from clay mineralogists, environmental scientists, and chemical engineers. In this study, the interactions between a cationic dye toluidine blue (TB) and palygorskite and sepiolite were investigated under different experimental [...] Read more.

Interactions between cationic dyes and negatively charged mineral surfaces have long attracted great attention from clay mineralogists, environmental scientists, and chemical engineers. In this study, the interactions between a cationic dye toluidine blue (TB) and palygorskite and sepiolite were investigated under different experimental conditions. The results showed that in addition to cation exchange, the specific surface area (SSA) of the minerals, particularly the formation of dimer molecules on the surface of both minerals, also accounted for the much higher TB uptake in comparison to their cation exchange capacities (CEC). The TB molecules were sorbed to the external surfaces, as no d-spacing expansion was observed in X-ray diffraction analyses. FTIR analyses showed strong interactions between the C=N or N-(CH₃)₂ group and the mineral surfaces, suggesting net electrostatic interactions if either of these functional groups bears a positive charge. Results from molecular dynamic simulations suggested dense monolayer TB formation on palygorskite because of its limited SSA and large CEC values. In comparison, a loosely dimeric formation was revealed on sepiolite for its large SSA and limited CEC values. Therefore, palygorskite is a better carrier for the sorption of cationic dyes, as evidenced by Maya blue paintings. Full article

(This article belongs to the Special Issue Characteristics of Raw Materials Used for Alkaline Activation and Geopolymerization Processes)

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13 pages, 3566 KiB

Open AccessArticle

Effect of Ni, N Co-Doped on Properties of AgSnO₂ Contact Materials

by Jingqin Wang, Jianyu Yang, Yancai Zhu, Guangzhi Zhang, Delin Hu and Guanglin Huang

Crystals 2021, 11(6), 707; https://doi.org/10.3390/cryst11060707 - 20 Jun 2021

Cited by 5 | Viewed by 2146

Abstract

The first-principles method based on density functional theory was used to analyze the impurity formation energies, energy bands, density of states, electron overlap population and elastic modulus of SnO₂, SnO₂–Ni, SnO₂–N and SnO₂–Ni–N. SnO₂ [...] Read more.

The first-principles method based on density functional theory was used to analyze the impurity formation energies, energy bands, density of states, electron overlap population and elastic modulus of SnO₂, SnO₂–Ni, SnO₂–N and SnO₂–Ni–N. SnO₂ powders with different additives were prepared by the sol-gel method, and then X-ray diffraction experiments and wettability experiments were carried out. The powder metallurgy method was used to prepare AgSnO₂ contacts with different additives. The simulation experiments on hardness, electrical conductivity and electrical contact were carried out. The simulation results show that the conductivity of Ni–N co-doped SnO₂ is best, and more impurity levels are introduced into the forbidden band, thereby increasing the carrier concentration, reducing the band gap, and improving the conductivity. The experimental results show that Ni, N doping does not change the structure of SnO₂, so doped SnO₂ still belongs to the tetragonal system. Ni–N co-doping can better improve the wettability between SnO₂ and Ag, reduce the accumulation of SnO₂ on the contact surface and reduce the contact resistance. Ni–N co-doped SnO₂ has the smallest hardness, improving ductility, molding and service life of the AgSnO₂ contact material. Full article

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17 pages, 6174 KiB

Open AccessArticle

Bentonites in Southern Spain. Characterization and Applications

by Jorge Luis Costafreda and Domingo Alfonso Martín

Crystals 2021, 11(6), 706; https://doi.org/10.3390/cryst11060706 - 20 Jun 2021

Cited by 14 | Viewed by 2830

Abstract

The objective of this work was to investigate and demonstrate the pozzolanic properties of the bentonites found at the San José–Los Escullos deposit, located in the southeast of the Iberian Peninsula, to be used in the manufacturing of more durable and environmentally compatible [...] Read more.

The objective of this work was to investigate and demonstrate the pozzolanic properties of the bentonites found at the San José–Los Escullos deposit, located in the southeast of the Iberian Peninsula, to be used in the manufacturing of more durable and environmentally compatible pozzolanic cements, mortars and concretes. These bentonites are mainly composed of smectites, with montmorillonite as the main clay mineral. They were formed by the hydrothermal alteration of tuffs, volcanic glasses, dacites, rhyolites and andesites. For this research, samples were taken from outcrops on the south, north and west side of the San José–Los Escullos deposit, and in the Los Trancos deposit located 19.3 km to the northeast. All samples consisted of bentonites, except for a zeolite sample taken from the northern flank of the San José–Los Escullos deposit, which was used to contrast and compare the behaviour of bentonite in some of the analyses that were done. An investigation of the mineralogical, petrological, chemical and thermogravimetric characteristics of the samples was carried out using various methods, such as XRD, OA (Oriented aggregates), TGA, XRF, SEM and thin section petrography (TSP). In addition, a chemical analysis of pozzolanicity (CAP) was done at 8 and 15 days to determine the pozzolanic capacity of the samples. XRD, XRF, SEM and TSP studies showed that these bentonites have a complex mineralogical constitution, composed mainly of smectites of the montmorillonite variety, as well as halloysite, illite, vermiculite, biotite, muscovite, kaolinite, chlorite, mordenite, feldspar, pyroxene, amphibole, calcite, volcanic glass and quartz. Thermogravimetric analysis (TGA) established the thermal stability of the bentonites studied at above 800 °C. Chemical analysis of pozzolanicity (CAP) confirmed the pozzolanic character of the bentonites, exhibited in their reactive behaviour with Ca(OH)₂. The pozzolanic reactivity increased significantly from 8 to 15 days. These results show that the materials studied can be used as quality pozzolans for the manufacture of pozzolanic cements, mortars and concretes. Full article

(This article belongs to the Special Issue Mineralogical Crystallography (2nd Edition))

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10 pages, 3611 KiB

Open AccessArticle

Effect of High Pressure and Temperature on the Evolution of Si Phase and Eutectic Spacing in Al-20Si Alloys

by Rong Zhang, Chunming Zou, Zunjie Wei and Hongwei Wang

Crystals 2021, 11(6), 705; https://doi.org/10.3390/cryst11060705 - 20 Jun 2021

Cited by 7 | Viewed by 2189

Abstract

The microstructure of the Si phase in Al-20Si alloys solidified under high pressure was investigated. The results demonstrate that the morphology of Si phase transformed (bulk→short rod→long needle) with the increase of superheat temperature under high pressure. At a pressure of 3 GPa [...] Read more.

The microstructure of the Si phase in Al-20Si alloys solidified under high pressure was investigated. The results demonstrate that the morphology of Si phase transformed (bulk→short rod→long needle) with the increase of superheat temperature under high pressure. At a pressure of 3 GPa and a superheat temperature of 100 K, a microstructure with a uniform distribution of fine Si phases on the α-Al matrix was obtained in the Al-20Si alloy. In addition, a mathematical model was developed to analyze the spacing variation of the lamellar Al-Si eutectics under the effect of pressure. The lamellar Al-Si eutectics appeared at 2 GPa and superheat temperatures of 70–150 K, and at 3 GPa and superheat temperatures of 140–200 K. With the increase of pressure from 2 GPa to 3 GPa, the average spacing of lamellar Al-Si eutectics decreased from 1.2–1.6 μm to 0.9–1.1 μm. In binary alloys, the effect of pressure on the eutectic spacing is related to the volume change of the solute phase from liquid to solid. When the volume change of the solute phase from liquid to solid is negative, the lamellar eutectic spacing decreases with increasing pressure. When it is positive, the eutectic spacing increases with increasing pressure. Full article

(This article belongs to the Special Issue Properties of Transition Metals and Their Compounds at Extreme Conditions)

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23 pages, 6025 KiB

Open AccessReview

Crystal Chemistry and Structural Complexity of the Uranyl Carbonate Minerals and Synthetic Compounds

by Vladislav V. Gurzhiy, Sophia A. Kalashnikova, Ivan V. Kuporev and Jakub Plášil

Crystals 2021, 11(6), 704; https://doi.org/10.3390/cryst11060704 - 19 Jun 2021

Cited by 17 | Viewed by 3681

Abstract

Uranyl carbonates are one of the largest groups of secondary uranium(VI)-bearing natural phases being represented by 40 minerals approved by the International Mineralogical Association, overtaken only by uranyl phosphates and uranyl sulfates. Uranyl carbonate phases form during the direct alteration of primary U [...] Read more.

Uranyl carbonates are one of the largest groups of secondary uranium(VI)-bearing natural phases being represented by 40 minerals approved by the International Mineralogical Association, overtaken only by uranyl phosphates and uranyl sulfates. Uranyl carbonate phases form during the direct alteration of primary U ores on contact with groundwaters enriched by CO₂, thus playing an important role in the release of U to the environment. The presence of uranyl carbonate phases has also been detected on the surface of “lavas” that were formed during the Chernobyl accident. It is of interest that with all the importance and prevalence of these phases, about a quarter of approved minerals still have undetermined crystal structures, and the number of synthetic phases for which the structures were determined is significantly inferior to structurally characterized natural uranyl carbonates. In this work, we review the crystal chemistry of natural and synthetic uranyl carbonate phases. The majority of synthetic analogs of minerals were obtained from aqueous solutions at room temperature, which directly points to the absence of specific environmental conditions (increased P or T) for the formation of natural uranyl carbonates. Uranyl carbonates do not have excellent topological diversity and are mainly composed of finite clusters with rigid structures. Thus the structural architecture of uranyl carbonates is largely governed by the interstitial cations and the hydration state of the compounds. The information content is usually higher for minerals than for synthetic compounds of similar or close chemical composition, which likely points to the higher stability and preferred architectures of natural compounds. Full article

(This article belongs to the Special Issue Mineralogical Crystallography (2nd Edition))

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16 pages, 3676 KiB

Open AccessArticle

Improvement of Drug-Loading Properties of Hydroxyapatite Particles Using Triethylamine as a Capping Agent: A Novel Approach

by Yi Wen, Jinsheng Li, Haotian Lin, Hao Huang, Keke Song, Ke Duan, Tailin Guo and Jie Weng

Crystals 2021, 11(6), 703; https://doi.org/10.3390/cryst11060703 - 18 Jun 2021

Cited by 17 | Viewed by 2754

Abstract

Particles that modify delivery characteristics are a focus of drug-loading research. Hydroxyapatite particles (HAPs) have excellent biocompatibility, shape controllability, and high adsorption, making them a potential candidate for drug-delivery carriers. However, there are still some defects in the current methods used to prepare [...] Read more.

Particles that modify delivery characteristics are a focus of drug-loading research. Hydroxyapatite particles (HAPs) have excellent biocompatibility, shape controllability, and high adsorption, making them a potential candidate for drug-delivery carriers. However, there are still some defects in the current methods used to prepare HAPs. In order to avoid agglomeration and improve the drug-loading properties of HAPs, the present study provides a novel triethylamine (TEA)-capped coprecipitation template method to prepare HAPs at room temperature. In addition, pure water and anhydrous ethanol were used as solvents to investigate the capping effect of the small-molecule capping agent TEA during the synthesis of HAPs. The results showed that the HAPs prepared in the TEA ethanol system had a smaller particle size (150–250 nm), better dispersion and higher crystallinity. The results were significantly different from those of the conventional preparation methods without TEA. However, the hydroxyapatite crystal would agglomerate to a certain extent after being stored for a period of time, forming micro/nano-sized agglomerates of nanocrystals. FITR analysis and SEM observation showed that the capping effect of TEA promoted the formation of a smaller template and dispersed HAPs were quickly formed by dissolution and reprecipitation processes. The drug-loading experiments showed that the HAPs prepared in the TEA ethanol system had high drug-loading capacity (239.8 ± 13.4 mg·g⁻¹) as well as an improved drug-release profile demonstrated in the drug-release experiment. The larger specific surface area associated with the smaller particle size was beneficial to the adsorption of drugs. After drying at 60 °C, TEA was evaporated from the HAPs which agglomerated into larger micron particles with more drug encapsulated. Thus, the effect of a sustained release was achieved. In the present research, a novel approach was developed by using triethylamine as the capping agent to prepare micro/nano-sized agglomerates of HAP nanocrystals with improved drug loading, which is predicted to have potential application in drug delivery. Full article

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10 pages, 61605 KiB

Open AccessArticle

In-Situ Reduction of Mo-Based Composite Particles during Laser Powder Bed Fusion

by Suxia Guo, Weiwei Zhou, Zhenxing Zhou, Yuchi Fan, Wei Luo and Naoyuki Nomura

Crystals 2021, 11(6), 702; https://doi.org/10.3390/cryst11060702 - 18 Jun 2021

Cited by 4 | Viewed by 2666

Abstract

Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds [...] Read more.

Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds from powders using carbon nanotubes (CNTs) and H₂ reduction. Spherical 1.5 wt.% CNT/Mo composite powders with uniform dispersion were fabricated via FD-POEM. The quantity of MoO₂ decreased significantly, and a hexagonally structured Mo₂C phase was simultaneously formed in the L-PBF build. The Mo₂C with network structure was distributed along the boundaries of equiaxed Mo grains, leading to an increased Vickers hardness of the matrix. This study demonstrates the feasibility of fabricating oxygen-free and high-strength refractory parts during L-PBF for ultrahigh-temperature applications. Full article

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

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11 pages, 4616 KiB

Open AccessArticle

Effect of Batchelor Flow on Polymorphic Crystallization in a Rotating Disk Crystallizer

by Zun-Hua Li, Jinsoo Kim and Woo-Sik Kim

Crystals 2021, 11(6), 701; https://doi.org/10.3390/cryst11060701 - 18 Jun 2021

Cited by 2 | Viewed by 2632

Abstract

In this work, the influence of Batchelor flow on the polymorphic crystallization in a rotating disk (RD) crystallizer was investigated. By regulating crystallization parameters, i.e., the rotation speed, cooling rate, and ethanol fraction, we found that a higher fraction of L-histidine stable Form-A [...] Read more.

In this work, the influence of Batchelor flow on the polymorphic crystallization in a rotating disk (RD) crystallizer was investigated. By regulating crystallization parameters, i.e., the rotation speed, cooling rate, and ethanol fraction, we found that a higher fraction of L-histidine stable Form-A at the induction time and a faster rate of phase transformation could be obtained in the RD crystallizer as compared to previous results in a mixing tank crystallizer. Based on these results, we concluded that the polymorphic crystallization in the RD crystallizer was more effective due to Batchelor flow fluid motion. Full article

(This article belongs to the Special Issue Pharmaceutical Crystallization)

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22 pages, 9774 KiB

Open AccessArticle

Balanced Mechanical and Tribological Performance of High-Frequency-Sintered Al-SiC Achieved via Innovative Milling Route—Experimental and Theoretical Study

by Ahmed Fouly, Saud M. Almotairy, Muhammad Omer Aijaz, Hamad F. Alharbi and Hany S. Abdo

Crystals 2021, 11(6), 700; https://doi.org/10.3390/cryst11060700 - 18 Jun 2021

Cited by 13 | Viewed by 2607

Abstract

In this study, Al-SiC nanocomposite was fabricated via powder metallurgy route using different innovative high-energy ball-milling techniques (HEBM). The powder mixture was consolidated using high-frequency induction heat sintering process (HFIHS). With the aim of studying the physical, mechanical, and tribological performance of the [...] Read more.

In this study, Al-SiC nanocomposite was fabricated via powder metallurgy route using different innovative high-energy ball-milling techniques (HEBM). The powder mixture was consolidated using high-frequency induction heat sintering process (HFIHS). With the aim of studying the physical, mechanical, and tribological performance of the fabricated nanocomposites. Relative density, hardness, compressive yield strength, Young’s modulus, toughness, elongation, specific wear rate and coefficient of friction were experimentally investigated. A finite element model for the frictional process was built to find out the distribution of contact stresses as result of samples sliding. It was found that the highest the energy of the milling, the more improvement in the mechanical and tribological performance could significantly achieved due to the homogeneous distribution and the excellent bonding effect of the composite. In addition, field emission scanning electron microscope was used for studying the sliding surface morphology in order to explicate the mechanism of the dry wear process. Full article

(This article belongs to the Special Issue Advances in Nanocomposites and Alloys in Saudi Arabia)

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15 pages, 20781 KiB

Open AccessArticle

Tautomeric Equilibrium of an Asymmetric β-Diketone in Halogen-Bonded Cocrystals with Perfluorinated Iodobenzenes

by Valentina Martinez, Nikola Bedeković, Vladimir Stilinović and Dominik Cinčić

Crystals 2021, 11(6), 699; https://doi.org/10.3390/cryst11060699 - 18 Jun 2021

Cited by 7 | Viewed by 2940

Abstract

In order to study the effect of halogen bond on tautomerism in β-diketones in the solid-state, we have prepared a series of cocrystals derived from an asymmetric β-diketone, benzoyl-4-pyridoylmethane (b4pm), as halogen bond acceptor and perfluorinated iodobenzenes: iodopentaflourobenzene (ipfb), [...] Read more.

In order to study the effect of halogen bond on tautomerism in β-diketones in the solid-state, we have prepared a series of cocrystals derived from an asymmetric β-diketone, benzoyl-4-pyridoylmethane (b4pm), as halogen bond acceptor and perfluorinated iodobenzenes: iodopentaflourobenzene (ipfb), 1,2-, 1,3- and 1,4-diiodotetraflorobenzene (12tfib, 13tfib and 14tfib) and 1,3,5-triiodo-2,4,6-trifluorobenzene (135titfb). All five cocrystals are assembled by I···N halogen bonds involving pyridyl nitrogen and iodoperfluorobenzene iodine resulting in 1:1 (four compounds) or 1:2 (one compound) cocrystal stoichiometry. Tautomer of b4pm in which hydrogen atom is adjacent to the pyridyl fragment was found to be more stable in vacuo than tautomer with a benzoyl hydroxyl group. This tautomer is also found to be dominant in the majority of crystal structures, somewhat more abundantly in crystal structures of cocrystals in which additional I···O halogen bond with the benzoyl oxygen has been established. Attempts have also been made to prepare an equivalent series of cocrystals using a closely related asymmetric β-diketone, benzoyl-3-pyridoylmethane (b3pm); however, all attempts were unsuccessful, which is attributed to more effective crystal packing of b3pm isomer compared to b4pm, which reduced the probability of cocrystal formation. Full article

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

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13 pages, 2456 KiB

Open AccessArticle

Optomechanically Induced Transparency and Slow–Fast Light Effect in Hybrid Cavity Optomechanical Systems

by Qinghong Liao, Weida Bao, Xing Xiao, Wenjie Nie and Yongchun Liu

Crystals 2021, 11(6), 698; https://doi.org/10.3390/cryst11060698 - 18 Jun 2021

Cited by 3 | Viewed by 2629

Abstract

We theoretically investigate the optomechanically induced transparency (OMIT) phenomenon and the fast and slow light effects of a four-mode optomechanical system with the Kerr medium. The optomechanical system is composed of an array of three single-mode cavities and a mechanical oscillator. The three [...] Read more.

We theoretically investigate the optomechanically induced transparency (OMIT) phenomenon and the fast and slow light effects of a four-mode optomechanical system with the Kerr medium. The optomechanical system is composed of an array of three single-mode cavities and a mechanical oscillator. The three cavities are a passive cavity, a no-loss-gain cavity and a gain optical cavity, respectively. A Kerr medium is inserted in the passive cavity. We study the influence of the Kerr medium on the stability of the optomechanical system, and find that the stable regime of the optomechanical system can be adjusted by changing the Kerr coefficient. We demonstrate that the phenomenon of optomechanically induced transparency will appear when the Kerr medium exists in the optomechanical system and find that the frequency position of the absorption peak on the left increases linearly with the Kerr coefficient. In addition, we also investigate the fast and slow light effects in this system. The results show that we can control the fast and slow light by adjusting the Kerr coefficient, tunneling strength, and driving field strength. This study has potential application prospects in the fields of quantum optical devices and quantum information processing. Full article

(This article belongs to the Special Issue Frontiers of Optomechanics of Nanocrystals)

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11 pages, 3087 KiB

Open AccessArticle

Chalcogen S∙∙∙S Bonding in Supramolecular Assemblies of Cadmium(II) Coordination Polymers with Pyridine-Based Ligands

by Nives Matijaković Mlinarić, Nikolina Penić, Boris-Marko Kukovec and Marijana Đaković

Crystals 2021, 11(6), 697; https://doi.org/10.3390/cryst11060697 - 18 Jun 2021

Cited by 1 | Viewed by 2365

Abstract

Two cadmium(II) coordination polymers, with thiocyanate and pyridine-based ligands e.g., 3-acetamidopyridine (3-Acpy) and niazid (nicotinic acid hydrazide, nia), namely one-dimensional {[Cd(SCN)₂(3-Acpy)]}_n (1) and two-dimensional {[Cd(SCN)₂(nia)]}_n (2), are prepared in the mixture of water [...] Read more.

Two cadmium(II) coordination polymers, with thiocyanate and pyridine-based ligands e.g., 3-acetamidopyridine (3-Acpy) and niazid (nicotinic acid hydrazide, nia), namely one-dimensional {[Cd(SCN)₂(3-Acpy)]}_n (1) and two-dimensional {[Cd(SCN)₂(nia)]}_n (2), are prepared in the mixture of water and ethanol. The adjacent cadmium(II) ions in 1 are bridged by two N,S-thiocyanate ions and an N,O-bridging 3-Acpy molecule, forming infinite one-dimensional polymeric chains, which are assembled by the intermolecular N–H∙∙∙S hydrogen bonds in one direction and by the intermolecular S∙∙∙S chalcogen bonds in another direction. Within the coordination network of 2, the adjacent cadmium(II) ions are bridged by N,S-thiocyanate ions in one direction and by N,O,N’-chelating and bridging nia molecules in another direction. The coordination networks of 2 are assembled by the intermolecular N–H∙∙∙S and N–H∙∙∙N hydrogen bonds and S∙∙∙S chalcogen bonds. Being the only supramolecular interactions responsible for assembling the polymer chains of 1 in the particular direction, the chalcogen S∙∙∙S bonds are more significant in the structure of 1, whilst the chalcogen S∙∙∙S bonds which act in cooperation with the N–H∙∙∙S and N–H∙∙∙N hydrogen bonds are of less significance in the structure of 2. Full article

(This article belongs to the Special Issue Coordination Polymers)

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9 pages, 2574 KiB

Open AccessArticle

Refinement of the Congruently Melting Composition of Nonstoichiometric Fluorite Crystals Ca_1-xY_xF_2x (x = 0.01–0.14)

by Denis N. Karimov, Elena A. Sulyanova and Boris P. Sobolev

Crystals 2021, 11(6), 696; https://doi.org/10.3390/cryst11060696 - 17 Jun 2021

Cited by 1 | Viewed by 1847

Abstract

The concentration series of nonstoichiometric crystals Ca₁_–_xY_xF_2+x (x = 0.01–0.14) was obtained from a melt by directional crystallization to refine the composition of the temperature maximum on the melting curves. A precision (±9 × [...] Read more.

The concentration series of nonstoichiometric crystals Ca₁_–_xY_xF_2+x (x = 0.01–0.14) was obtained from a melt by directional crystallization to refine the composition of the temperature maximum on the melting curves. A precision (±9 × 10⁻⁵ Å) determination of lattice parameters of the Ca₁_–_xY_xF_2+x crystals with the structure of fluorite (sp. gr. Fm-3m) was performed, and a linear equation of their concentration dependence was calculated: a(x) = 5.46385(5) + 0.1999(4) x. The distribution of yttrium along the crystals Ca₁_–_xY_xF_2+x, the content of which is determined by the precision lattice parameters, is studied. The congruently melting composition x = 0.105(5) of the Ca₁_–_xY_xF_2+x phase is refined by the method of directional crystallization. Full article

(This article belongs to the Special Issue Functional Materials Based on Rare-Earth Elements)

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29 pages, 7087 KiB

Open AccessReview

Design Strategy for Recycled Aggregate Concrete: A Review of Status and Future Perspectives

by Natt Makul, Roman Fediuk, Mugahed Amran, Abdullah M. Zeyad, Sergey Klyuev, Irina Chulkova, Togay Ozbakkaloglu, Nikolai Vatin, Maria Karelina and Afonso Azevedo

Crystals 2021, 11(6), 695; https://doi.org/10.3390/cryst11060695 - 17 Jun 2021

Cited by 65 | Viewed by 7602

Abstract

Currently, a number of disadvantages hampers the use of recycled concrete aggregates (RCA). The current review proves that concretes made with complete replacement of natural aggregate with RCA allow the production of high-quality concrete. One of the possibilities for improving concrete properties with [...] Read more.

Currently, a number of disadvantages hampers the use of recycled concrete aggregates (RCA). The current review proves that concretes made with complete replacement of natural aggregate with RCA allow the production of high-quality concrete. One of the possibilities for improving concrete properties with RCA is the use of extended curing and pozzolanic materials with varying cement ratios. The potential use of RCA concretes is in the production of high-value materials that increase environmental and financial benefits. RCA have strong potential in the development of a new generation of concrete and stimulate economic activity in many countries in addition to optimizing natural resources. Economic benefits include minimal travel costs; cheaper sources of concrete than newly mined aggregates; reduction of the landfill area required for the placement of concrete waste; the use of RCA minimizes the need for gravel extraction, etc. The proposed strategy could be to sequentially separate demolition waste such as roof finishes, waterproof materials, interior and exterior materials, etc. Closing life cycles is the main approach used for efficient structures for the recycling and reuse of construction and demolition waste in the production and recovery of materials, especially when recycling and reusing materials. In the life cycle, the recycling of recovered materials allows them to be used for new construction purposes, avoiding the use of natural concrete aggregates. Government, design institutes, construction departments and project managers should be involved in the creation and use of RCA. In demolition and construction, the main players are the project owners. Their obligations, expectations and responsibilities must be properly aligned. For the past 20 years, recycled concrete aggregate from demolition and construction waste has been considered as an alternative to pure concrete in structural concrete to minimize the environmental impact of construction waste and demolition waste and the conversion of natural aggregate resources. It is now recognized that the use of RCA for the generations of concrete is a promising and very attractive technology for reducing the environmental impact of the construction sector and conserving natural resources. In the market, the selling price is not an obstacle for market applications of RCA, as there are scenarios in which their cost is lower than the cost of products made from conventional building materials. This is more of an acceptance factor in the market for recycled concrete aggregates. In this sector, the lack of identification, accreditation and uniform quality certification systems and their narrow application cause some marketing problems. With proper RCA preparation, concrete with standard physical and mechanical properties and performance characteristics can be obtained. Full article

(This article belongs to the Special Issue Research of Construction and Building Materials in Peter the Great St. Petersburg Polytechnic University in Crystals)

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10 pages, 3656 KiB

Open AccessArticle

Magnetism and Thermomechanical Properties in Si Substituted MnCoGe Compounds

by Abdul Rashid Abdul Rahman, Muhamad Faiz Md Din, Jianli Wang, Nur Sabrina Suhaimi, Nurul Hayati Idris, Shi Xue Dou, Mohammad Ismail, Muhammad Zahir Hassan and Mohd Taufik Jusoh

Crystals 2021, 11(6), 694; https://doi.org/10.3390/cryst11060694 - 17 Jun 2021

Cited by 10 | Viewed by 2361

Abstract

MnCoGe-based compounds have been increasingly studied due to their possible large magnetocaloric effect correlated to the magnetostructural coupling. In this research, a comprehensive study of structure, magnetic phase transition, magnetocaloric effect and thermomechanical properties for MnCoGe_1−xSi_x is reported. Room temperature [...] Read more.

MnCoGe-based compounds have been increasingly studied due to their possible large magnetocaloric effect correlated to the magnetostructural coupling. In this research, a comprehensive study of structure, magnetic phase transition, magnetocaloric effect and thermomechanical properties for MnCoGe_1−xSi_x is reported. Room temperature X-ray diffraction indicates that the MnCoGe_1−xSi_x (x = 0, 0.05, 0.1, 0.15 and 0.2) alloys have a major phase consisting of an orthorhombic TiNiSi-type structure with increasing lattice parameter b and decreasing others (a and c) with increasing Si concentration. Along with M-T and DSC measurements, it is indicated that the T_c value increased with higher Si concentration and decreased for structural transition temperature T_str. The temperature dependence of the magnetization curves overlaps completely, indicating that there is no thermal hysteresis, and it is shown that the transition is the second-order type. It is also shown that the decreased magnetization on the replacement of Si for Ge decreases the value of −ΔS_M from −ΔS_M~8.36 J kg⁻¹ K⁻¹ at x = 0 to −ΔS_M~5.49 J kg⁻¹ K⁻¹ at x = 0.2 with 5 T applied field. The performed Landau theory has confirmed the second-order transition in this study, which is consistent with the Banerjee criterion. The magnetic measurement and thermomechanical properties revealed the structural transition that takes place with Si substitution of Ge. Full article

(This article belongs to the Special Issue Magnetocaloric Effect and Giant Negative Thermal Expansion)

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16 pages, 8809 KiB

Open AccessArticle

Interactions of Ruddlesden-Popper Phases and Migration-Induced Field-Stabilized Polar Phase in Strontium Titanate

by Christian Ludt, Elena Ovchinnikova, Anton Kulikov, Dmitri Novikov, Sibylle Gemming, Dirk C. Meyer and Matthias Zschornak

Crystals 2021, 11(6), 693; https://doi.org/10.3390/cryst11060693 - 17 Jun 2021

Cited by 2 | Viewed by 2815

Abstract

This work focuses on the validation of a possible connection of the known Ruddlesden-Popper (RP) phases and the novel concept of the migration-induced field-stabilized polar (MFP) phase. To study this subject, model structures of RP phases in bulk strontium titanate are analyzed by [...] Read more.

This work focuses on the validation of a possible connection of the known Ruddlesden-Popper (RP) phases and the novel concept of the migration-induced field-stabilized polar (MFP) phase. To study this subject, model structures of RP phases in bulk strontium titanate are analyzed by means of density functional theory (DFT). The obtained geometries are compared to experimental MFP data. Good agreement can be found concerning atomic displacements in the pm range and lattice strain inferred by the RP phases. Looking at the energy point of view, the defect structures are on the convex hull of the Gibb’s free energy. Although the dynamics to form the discussed defect models are not addressed in detail, the interplay and stability of the described defect model will add to the possible structure scenarios within the near-surface region of strontium titanate. As a result, it can be suggested that RP phases generally favor the MFP formation. Full article

(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)

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17 pages, 5743 KiB

Open AccessArticle

Influence of Polyvinyl Alcohol Powder on the Mechanical Performance and Volume Stability of Sulfoaluminate–Portland Cement Composite

by Yuhong He, Liwu Mo, Zhongyang Mao, Fufan Huang and Zhenghao Han

Crystals 2021, 11(6), 692; https://doi.org/10.3390/cryst11060692 - 17 Jun 2021

Cited by 4 | Viewed by 2556

Abstract

Cement quick repair materials generally have the defects of brittleness and early shrinkage. The modification of composite cement mortar by water-soluble glue powder—polyvinyl alcohol (PVA)—was studied in the condition of settled water cement ratio. At 90 days, the maximum flexural strength of mortar [...] Read more.

Cement quick repair materials generally have the defects of brittleness and early shrinkage. The modification of composite cement mortar by water-soluble glue powder—polyvinyl alcohol (PVA)—was studied in the condition of settled water cement ratio. At 90 days, the maximum flexural strength of mortar was 15.4 MPa, which was 1.3 times of the group without PVA and there was no strength shrinkage phenomenon. Through the analysis of the porosity, PVA improved the total porosity; high porosity could play a better role of buffering and absorbing the impact stress, effectively improving the toughness of mortar. At 28 days, the maximum impact resistance was 1.72 J/cm², which was 1.75 times of the group without PVA. In addition, the increased total porosity also greatly absorbed the shrinkage stress at the early stage, and reduced the mortar self-shrinkage. When the PVA content was 1%, the volume self-shrinkage of mortar decreased from the initial 3360 μm·m⁻¹ to 700 μm·m⁻¹. According to the analysis of hydration heat, the addition of PVA effectively reduced the early hydration heat release rate and alleviated the concentrated heat release phenomenon to a certain extent. In this paper, the hydration reaction of composite cement and the action mechanism of PVA in composite cement were studied by means of X-ray diffraction, infrared spectrum and hydration heat analysis. Full article

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11 pages, 2299 KiB

Open AccessArticle

Ice Coverage Induced by Depositing a Water Drop onto the Supercooled Substrate at Extreme Low Vapor Pressure

by Yugang Zhao, Zichao Zuo, Haibo Tang and Xin Zhang

Crystals 2021, 11(6), 691; https://doi.org/10.3390/cryst11060691 - 17 Jun 2021

Cited by 5 | Viewed by 2284

Abstract

Icing/snowing/frosting is ubiquitous in nature and industrial processes, and the accretion of ice mostly leads to catastrophic consequences. The existing understanding of icing is still limited, particularly for aircraft icing, where direct observation of the freezing dynamics is inaccessible. In this work, we [...] Read more.

Icing/snowing/frosting is ubiquitous in nature and industrial processes, and the accretion of ice mostly leads to catastrophic consequences. The existing understanding of icing is still limited, particularly for aircraft icing, where direct observation of the freezing dynamics is inaccessible. In this work, we investigate experimentally the impact and freezing of a water drop onto the supercooled substrate at extremely low vapor pressure, to mimic an aircraft passing through clouds at a relatively high altitude, engendering icing upon collisions with pendant drops. Special attention is focused on the ice coverage induced by an impinging drop, from the perimeter pointing outward along the radial direction. We observed two freezing regimes: (I) spread-recoil-freeze at the substrate temperature of T_s = −15.4 ± 0.2 °C and (II) spread (incomplete)-freeze at the substrate temperature of T_s = −22.1 ± 0.2 °C. The ice coverage is approximately one order of magnitude larger than the frozen drop itself, and counterintuitively, larger supercooling yields smaller ice coverage in the range of interest. We attribute the variation of ice coverage to the kinetics of vapor diffusion in the two regimes. This fundamental understanding benefits the design of new anti-icing technologies for aircraft. Full article

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11 pages, 4163 KiB

Open AccessArticle

Low Temperature Transitional Aluminas: Structure Specifics and Related X-ray Diffraction Features

by Dmitriy A. Yatsenko, Vera P. Pakharukova and Sergey V. Tsybulya

Crystals 2021, 11(6), 690; https://doi.org/10.3390/cryst11060690 - 16 Jun 2021

Cited by 18 | Viewed by 4471

Abstract

Despite the fact that metastable aluminum oxides are actively used in industry, there is a discrepancy in the literature regarding their crystal structure. All this leads to difficulties in data interpretation and, as a consequence, classification problems. This work is aimed at solving [...] Read more.

Despite the fact that metastable aluminum oxides are actively used in industry, there is a discrepancy in the literature regarding their crystal structure. All this leads to difficulties in data interpretation and, as a consequence, classification problems. This work is aimed at solving these tasks. The main features of powder X-ray diffraction of typical samples of three Al₂O₃ polymorphs (γ-, χ-, η-) are analyzed. Specifics and fundamental differences in X-ray scattering and their relationship with the structural organization at the nanostructure level are clearly shown. The work demonstrates the possibilities of analyzing experimental powder X-ray diffraction data using a modern approach based on the Debye Scattering Equation for studying the organization of such complex systems. Full article

(This article belongs to the Special Issue Advanced Functional Oxide Ceramics)

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24 pages, 11448 KiB

Open AccessArticle

Stress–Strain Behavior of FRC in Uniaxial Tension Based on Mesoscopic Damage Model

by Weifeng Bai, Xiaofeng Lu, Junfeng Guan, Shuang Huang, Chenyang Yuan and Cundong Xu

Crystals 2021, 11(6), 689; https://doi.org/10.3390/cryst11060689 - 16 Jun 2021

Cited by 7 | Viewed by 2824

Abstract

Fiber-reinforced concrete (FRC) is widely used in the field of civil engineering. However, the research on the damage mechanism of FRC under uniaxial tension is still insufficient, and most of the constitutive relations are macroscopic phenomenological. The aim is to provide a new [...] Read more.

Fiber-reinforced concrete (FRC) is widely used in the field of civil engineering. However, the research on the damage mechanism of FRC under uniaxial tension is still insufficient, and most of the constitutive relations are macroscopic phenomenological. The aim is to provide a new method for the investigation of mesoscopic damage mechanism of FRC under uniaxial tension. Based on statistical damage theory, the damage constitutive model for FRC under uniaxial tension is established. Two kinds of mesoscopic damage mechanisms, fracture and yield, are considered, which ultimately determines the macroscopic nonlinear stress–strain behavior of concrete. The yield damage mode reflects the potential bearing capacity of materials and plays a key role in the whole process. Evolutionary factor is introduced to reflect the degree of optimization and adjustment of the stressed skeleton in microstructure. The whole deformation-to-failure is divided into uniform damage phase and local failure phase. It is assumed that the two kinds of damage evolution follow the independent triangular probability distributions, which could be represented by four characteristic parameters. The validity of the proposed model is verified by two sets of test data of steel fiber-reinforced concrete. Through the analysis of the variation law of the above parameters, the influence of fiber content on the initiation and propagation of micro-cracks and the damage evolution of concrete could be evaluated. The relations among physical mechanism, mesoscopic damage mechanism, and macroscopic nonlinear mechanical behavior of FRC are discussed. Full article

(This article belongs to the Special Issue Advances in Sustainable Concrete System)

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12 pages, 1128 KiB

Open AccessArticle

Synthesis, Structural Studies, and Anticancer Properties of [CuBr(PPh₃)₂(4,6-Dimethyl-2-Thiopyrimidine-κS]

by Bandar A. Babgi, Jalal H. Alsayari, Bambar Davaasuren, Abdul-Hamid Emwas, Mariusz Jaremko, Magda H. Abdellattif and Mostafa A. Hussien

Crystals 2021, 11(6), 688; https://doi.org/10.3390/cryst11060688 - 16 Jun 2021

Cited by 13 | Viewed by 3230

Abstract

CuBr(PPh₃)₂(4,6-dimethylpyrimidine-2-thione) (Cu-L) was synthesized by stirring CuBr(PPh₃)₃ and 4,6-dimethylpyrimidine-2-thione in dichloromethane. The crystal structure of Cu-L was obtained, and indicated that the complex adopts a distorted tetrahedral structure with several intramolecular hydrogen bonds. Moreover, a centrosymmetric [...] Read more.

CuBr(PPh₃)₂(4,6-dimethylpyrimidine-2-thione) (Cu-L) was synthesized by stirring CuBr(PPh₃)₃ and 4,6-dimethylpyrimidine-2-thione in dichloromethane. The crystal structure of Cu-L was obtained, and indicated that the complex adopts a distorted tetrahedral structure with several intramolecular hydrogen bonds. Moreover, a centrosymmetric dimer is formed by the intermolecular hydrogen bonding of the bromine acceptor created by symmetry operation 1−x, 1−y, 1−z to the methyl group (D₃ = C42) of the pyrimidine–thione ligand. HSA-binding of Cu-L and its ligand were evaluated, revealing that Cu-L binds to HSA differently than its ligand. The HSA-bindings were modeled by molecular docking, which suggested that Cu-L binds to the II A domain while L binds between the I B and II A domains. Anticancer activities toward OVCAR-3 and HeLa cell lines were tested and indicated the significance of the copper center in enhancing the cytotoxic effect; negligible toxicities for L and Cu-L were observed towards a non-cancer cell line. The current study highlights the potential of copper(I)-phosphine complexes containing thione ligands as therapeutic agents. Full article

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

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