Crystals

13 pages, 1813 KiB

Open AccessEditor’s ChoiceArticle

Comparative Hybrid Hartree-Fock-DFT Calculations of WO₂-Terminated Cubic WO₃ as Well as SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ (001) Surfaces

by R. I. Eglitis, Juris Purans and Ran Jia

Crystals 2021, 11(4), 455; https://doi.org/10.3390/cryst11040455 - 20 Apr 2021

Cited by 48 | Viewed by 4842

Abstract

We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO₂-terminated cubic WO₃ (001) surface and analyzed the systematic trends in the WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO [...] Read more.

We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO₂-terminated cubic WO₃ (001) surface and analyzed the systematic trends in the WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ (001) surface ab initio calculations. According to our first principles calculations, all WO₂ or TiO₂-terminated WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaZrO₃ (001) surface upper-layer atoms relax inwards towards the crystal bulk, while all second-layer atoms relax upwards. The only two exceptions are outward relaxations of first layer WO₂ and TiO₂-terminated WO₃ and PbTiO₃ (001) surface O atoms. The WO₂ or TiO₂-terminated WO₃, SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ (001) surface-band gaps at the Γ–Γ point are smaller than their respective bulk-band gaps. The Ti–O chemical bond populations in the SrTiO₃, BaTiO₃, PbTiO₃ and CaTiO₃ bulk are smaller than those near the TiO₂-terminated (001) surfaces. Conversely, the W–O chemical bond population in the WO₃ bulk is larger than near the WO₂-terminated WO₃ (001) surface. Full article

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

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17 pages, 6402 KiB

Open AccessArticle

Effect of the External Velocity on the Exfoliation Properties of Graphene from Amorphous SiO₂ Surface

by Qi Zhang, Xing Pang and Yulong Zhao

Crystals 2021, 11(4), 454; https://doi.org/10.3390/cryst11040454 - 20 Apr 2021

Cited by 5 | Viewed by 2149

Abstract

External action has a significant influence on the formation of high-quality graphene and the adhesion of graphene on the surface of the MEMS/NEMS device. The atomic-scale simulation and calculation can further study the exfoliation process of graphene by external actions. In multilayer graphene [...] Read more.

External action has a significant influence on the formation of high-quality graphene and the adhesion of graphene on the surface of the MEMS/NEMS device. The atomic-scale simulation and calculation can further study the exfoliation process of graphene by external actions. In multilayer graphene systems where graphene layers were simulated weakly contacted with SiO₂ substrate, a constant vertical upward velocity (V_up) was applied to the topmost layer. Then two critical velocities were found, and three kinds of distinct exfoliation processes determined by critical upward velocities were observed in multilayer graphene systems. The first critical velocities are in the range of 0.5 Å/ps–3.18 Å/ps, and the second critical velocities are in the range of 9.5 Å/ps–12.1 Å/ps. When the V_up is less than the first critical velocity, all graphene layers will not be exfoliated. When V_up is between the first and second critical V_up, all layers can be exfoliated almost synchronously at last. When V_up is larger than the second critical V_up, the topmost layer can be exfoliated alone, transferring energy to the underlying layers, and the underlying layers are slowly exfoliated. The maximum exfoliation force to exfoliate the topmost layer of graphene is 3200 times larger than that of all graphene layers. Moreover, it is required 149.26 mJ/m² to get monolayer graphene from multilayers, while peeling off all layers without effort. This study explains the difficulty to get monolayer graphene and why graphene falls off easily during the transfer process. Full article

(This article belongs to the Special Issue Nanocarbon Materials for Biological Application)

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14 pages, 1347 KiB

Open AccessReview

Strain Accommodations among Twin Variants in Ti and Mg

by Ping Zhou and Guo-Zhen Zhu

Crystals 2021, 11(4), 453; https://doi.org/10.3390/cryst11040453 - 20 Apr 2021

Cited by 5 | Viewed by 2414

Abstract

The selection of twin variants has a great influence on deformation texture and mechanical property in hcp metals where slip systems are limited and twinning types are abundant during deformation. Local strain accommodations among twin variants are considered to shed light on variant [...] Read more.

The selection of twin variants has a great influence on deformation texture and mechanical property in hcp metals where slip systems are limited and twinning types are abundant during deformation. Local strain accommodations among twin variants are considered to shed light on variant selection rules in Ti and Mg alloys. Five kinds of strain accommodations are discussed in terms of different regions that are affected by the twinning shear of primary twin. These regions contain (I) the whole sample, (II) neighboring grain, (III) adjacent primary twin in neighboring grain, (IV) adjoining primary twin within the same parent grain, and (V) multi-generation of twinning inside the primary twin. For a potentially active variant, its operation needs not only relatively higher resolved shear stress but also easily accommodated strain by immediate vicinity. Many of the non-Schmid behaviors could be elucidated by local strain accommodations that variants with relatively higher SFs hard to be accommodated are absent, while those with relatively lower SFs but could be easily accommodated are present. Full article

(This article belongs to the Special Issue Crystalline Patterns as Bases for Design of Engineering Structures, Mechanisms and Metamaterials)

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13 pages, 13366 KiB

Open AccessArticle

P–V–T Equation of State of Iridium Up to 80 GPa and 3100 K

by Simone Anzellini, Leonid Burakovsky, Robin Turnbull, Enrico Bandiello and Daniel Errandonea

Crystals 2021, 11(4), 452; https://doi.org/10.3390/cryst11040452 - 20 Apr 2021

Cited by 45 | Viewed by 3809

Abstract

In the present study, the high-pressure high-temperature equation of the state of iridium has been determined through a combination of in situ synchrotron X-ray diffraction experiments using laser-heating diamond-anvil cells (up to 48 GPa and 3100 K) and density-functional theory calculations (up to [...] Read more.

In the present study, the high-pressure high-temperature equation of the state of iridium has been determined through a combination of in situ synchrotron X-ray diffraction experiments using laser-heating diamond-anvil cells (up to 48 GPa and 3100 K) and density-functional theory calculations (up to 80 GPa and 3000 K). The melting temperature of iridium at 40 GPa was also determined experimentally as being 4260 (200) K. The results obtained with the two different methods are fully consistent and agree with previous thermal expansion studies performed at ambient pressure. The resulting thermal equation of state can be described using a third-order Birch–Murnaghan formalism with a Berman thermal-expansion model. The present equation of the state of iridium can be used as a reliable primary pressure standard for static experiments up to 80 GPa and 3100 K. A comparison with gold, copper, platinum, niobium, rhenium, tantalum, and osmium is also presented. On top of that, the radial-distribution function of liquid iridium has been determined from experiments and calculations. Full article

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

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13 pages, 33624 KiB

Open AccessArticle

Structure-Properties Correlation of Cross-Linked Penicillin G Acylase Crystals

by Marta Kubiak, Janine Mayer, Ingo Kampen, Carsten Schilde and Rebekka Biedendieck

Crystals 2021, 11(4), 451; https://doi.org/10.3390/cryst11040451 - 20 Apr 2021

Cited by 7 | Viewed by 2428

Abstract

In biocatalytic processes, the use of free enzymes is often limited due to the lack of long-term stability and reusability. To counteract this, enzymes can be crystallized and then immobilized, generating cross-linked enzyme crystals (CLECs). As mechanical stability and activity of CLECs are [...] Read more.

In biocatalytic processes, the use of free enzymes is often limited due to the lack of long-term stability and reusability. To counteract this, enzymes can be crystallized and then immobilized, generating cross-linked enzyme crystals (CLECs). As mechanical stability and activity of CLECs are crucial, different penicillin G acylases (PGAs) from Gram-positive organisms have proven to be promising candidates for industrial production of new semisynthetic antibiotics, which can be crystallized and cross-linked to characterize the resulting CLECs regarding their mechanical and catalytic properties. The greatest hardness and Young’s modulus determined by indentation with an atomic force microscope were observed for CLECs of Bacillus species FJAT-PGA CLECs (26 MPa/1450 MPa), followed by BmPGA (Priestia megaterium PGA, 23 MPa/1170 MPa) and BtPGA CLECs (Bacillus thermotolerans PGA, 11 MPa/614 MPa). In addition, FJAT- and BtPGA CLECs showed up to 20-fold higher volumetric activities compared to BmPGA CLECs. Correlation to structural characteristics indicated that a high solvent content and low number of cross-linking residues might lead to reduced stability. Furthermore, activity seems to be restricted by small water channels due to severe diffusion limitations. To the best of our knowledge, we show for the first time in this study that the entire process chain for the characterization of diverse industrially relevant enzymes can be performed at the microliter scale to discover the most important relationships and limitations. Full article

(This article belongs to the Section Biomolecular Crystals)

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15 pages, 19513 KiB

Open AccessArticle

Effect of Fluoroalkyl-Substituent in Bistolane-Based Photoluminescent Liquid Crystals on Their Physical Behavior

by Shigeyuki Yamada, Yizhou Wang, Masato Morita, Qingzhi Zhang, David O’Hagan, Masakazu Nagata, Tomohiro Agou, Hiroki Fukumoto, Toshio Kubota, Mitsuo Hara and Tsutomu Konno

Crystals 2021, 11(4), 450; https://doi.org/10.3390/cryst11040450 - 20 Apr 2021

Cited by 4 | Viewed by 3030

Abstract

Photoluminescent liquid crystals (PLLCs) have attracted significant attention owing to their broad applicability in thermosensing and PL switching. Extensive efforts have been made to develop bistolane-based PLLCs containing flexible units at both molecular terminals, and it has been revealed that their PL behavior [...] Read more.

Photoluminescent liquid crystals (PLLCs) have attracted significant attention owing to their broad applicability in thermosensing and PL switching. Extensive efforts have been made to develop bistolane-based PLLCs containing flexible units at both molecular terminals, and it has been revealed that their PL behavior can switch with the phase transition between the crystalline and LC phases. Although slight modulation of the flexible unit structure dramatically alters the LC and PL behaviors, few studies into the modification of the flexible units have been conducted. With the aim of achieving dynamic changes in their physical behaviors, we developed a family of bistolane derivatives containing a simple alkyl or a fluoroalkyl flexible chain and carried out a detailed systematic evaluation of their physical behaviors. Bistolanes containing a simple alkyl chain showed a nematic LC phase, whereas switching the flexible chain in the bistolane to a fluoroalkyl moiety significantly altered the LC phase to generate a smectic phase. The fluoroalkyl-containing bistolanes displayed a stronger deep blue PL than their corresponding non-fluorinated counterparts, even in the crystalline phase, which was attributed to the construction of rigid molecular aggregates through intermolecular F···H and F···F interactions to suppress non-radiative deactivation. Full article

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

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11 pages, 4421 KiB

Open AccessArticle

Understanding the Reaction Crystallization Process of Glycidyl Trimethyl Ammonium Chloride

by Shuai Yu, Hui Chen, Xujie Gao, Weichun Feng, Wenguo Xing, Shichao Du, Yan Wang, Fumin Xue and Yan Cheng

Crystals 2021, 11(4), 449; https://doi.org/10.3390/cryst11040449 - 20 Apr 2021

Cited by 8 | Viewed by 2723

Abstract

Reaction crystallization to produce glycidyl trimethyl ammonium chloride (GTA) via epichlorohydrin with gas-state trimethylamine was investigated. The crystallization process of the GTA gas-liquid reaction was optimized by a seed method. The optimized technology can prepare GTA products with crystal form and purity greater [...] Read more.

Reaction crystallization to produce glycidyl trimethyl ammonium chloride (GTA) via epichlorohydrin with gas-state trimethylamine was investigated. The crystallization process of the GTA gas-liquid reaction was optimized by a seed method. The optimized technology can prepare GTA products with crystal form and purity greater than 97%. The crystallization process of GTA consists of four steps (i.e., addition of seed, dispersion of seed, growth of crystals on the seed surfaces, agglomeration and growth of crystal). Seed method and flow rate are the key factors affecting purity. The purity and particle size of GTA crystals were satisfactory as long as the operation was kept within the defined envelope. The experiments were conducted on a 1 L reactor and successfully scaled-up to 3000 L in industry. Full article

(This article belongs to the Special Issue Crystallization Process Design and Control: Intensification and Optimization)

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10 pages, 3591 KiB

Open AccessArticle

New Insight on Liquid Steel Microalloying by Pulse-Step Method in Two-Strand Slab Tundish by Numerical Simulations

by Adam Cwudziński

Crystals 2021, 11(4), 448; https://doi.org/10.3390/cryst11040448 - 20 Apr 2021

Cited by 2 | Viewed by 1835

Abstract

Developing a technology for introducing alloy addition to liquid steel during the course of continuous casting process seems to be an interesting approach to enhancing the steelmaking process, especially as the effective introduction of micro-additives or non-metallic inclusion modifiers to the liquid steel [...] Read more.

Developing a technology for introducing alloy addition to liquid steel during the course of continuous casting process seems to be an interesting approach to enhancing the steelmaking process, especially as the effective introduction of micro-additives or non-metallic inclusion modifiers to the liquid steel is the key to the production of the highest-quality steel. This paper presents the results of investigation describing the process of liquid steel chemical homogenisation in the two-strand slab tundish. The alloy was fed to liquid steel by pulse-step method. Five tundish equipment variants with different flow control devices and alloy addition feeding positions were considered. The paper includes fields of liquid steel flow, alloy concentration vs. time curves, dimensionless mixing time, minimum time values and alloy concentration deviations at tundish outlets. The results pointed much more effectively with liquid steel mixing nickel than aluminium. For aluminium obtaining a 95% chemical homogenisation level requires three-fold more time. Moreover, it is definitely beneficial for chemical homogenisation to initiate the alloying process simultaneously in two sites. This procedure generates, among others, the least alloy deviation of concentration at tundish outlets. Full article

(This article belongs to the Special Issue Liquid Steel Alloying Process)

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9 pages, 1523 KiB

Open AccessArticle

Displacements in the Cationic Motif of Nonstoichiometric Fluorite Phases Ba₁₋_xR_xF₂₊_x as a Result of the Formation of {Ba₈[R₆F_68–69]} Clusters: III. Defect Cluster Structure of the Nonstoichiometric Phase Ba_0.69La_0.31F_2.31 and Its Dependence on Heat Treatment

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

Crystals 2021, 11(4), 447; https://doi.org/10.3390/cryst11040447 - 20 Apr 2021

Cited by 8 | Viewed by 2045

Abstract

The defect structure of Ba_0.69La_0.31F_2.31 single crystals in as-grown state and after annealing at 1173 K for 336 h was studied by X-ray diffraction analysis. Both crystals belong to the CaF₂ structure type (sp. gr. [...] Read more.

The defect structure of Ba_0.69La_0.31F_2.31 single crystals in as-grown state and after annealing at 1173 K for 336 h was studied by X-ray diffraction analysis. Both crystals belong to the CaF₂ structure type (sp. gr.

F m \bar{3} m

). They have vacancies in the main anion motif and interstitial fluorine anions in Wyckoff positions 48i and 4b. Relaxation (static displacement of some main anions to Wyckoff position 32f) is observed in the annealed crystal. It was established that annealing leads to a change in the type of displacement of the main anions in Wyckoff positions 8c from dynamic to static. Displacement of La³⁺ cations to Wyckoff position 32f is observed in both crystals. A model of the defect structure of Ba_0.69La_0.31F_2.31 is proposed, according to which interstitial fluorine anions and La³⁺ cations are aggregated into [Ba_14−nLa_nF_64+n] clusters with the cuboctahedral anionic core formed by interstitial fluorine anions in Wyckoff positions 48i. Ba²⁺ cations are located in the cluster in the centers of the faces, and the La³⁺ cations are shifted by 0.24 Å from the vertices of the cluster along the three-fold axis towards the center of the cluster. The study establishes the relationship between the defect structure of crystals and their structurally sensitive properties, and to develop approaches to their management. Full article

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

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5 pages, 1093 KiB

Open AccessArticle

High Thermal Stability of κ-Ga₂O₃ Grown by MOCVD

by Junhee Lee, Honghyuk Kim, Lakshay Gautam and Manijeh Razeghi

Crystals 2021, 11(4), 446; https://doi.org/10.3390/cryst11040446 - 20 Apr 2021

Cited by 16 | Viewed by 3879

Abstract

We report a high thermal stability of kappa gallium oxide grown on c-plane sapphire substrate by metal organic chemical vapor deposition. Kappa gallium oxide is widely known as a metastable polymorph transitioning its phase when subjected to a high temperature. Here, we show [...] Read more.

We report a high thermal stability of kappa gallium oxide grown on c-plane sapphire substrate by metal organic chemical vapor deposition. Kappa gallium oxide is widely known as a metastable polymorph transitioning its phase when subjected to a high temperature. Here, we show the kappa gallium oxide whose phase is stable in a high temperature annealing process at 1000 °C. These oxide films were grown at 690 °C under nitrogen carrier gas. The materials showed high electrical resistivity when doped with silicon, whereas the film conductivity was significantly improved when doped with both indium and silicon. This work provides a pathway to overcoming limitations for the advance in utilizing kappa gallium oxide possessing superior electrical characteristics. Full article

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

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11 pages, 3209 KiB

Open AccessArticle

Stability, Elastic and Electronic Properties of Ta₂N by First-Principles Calculations

by Longpeng Zhu, Jiong Wang, Chenchen Dong, Yong Du, Shun-Li Shang and Zi-Kui Liu

Crystals 2021, 11(4), 445; https://doi.org/10.3390/cryst11040445 - 19 Apr 2021

Cited by 5 | Viewed by 2608

Abstract

Owing to exploring the influence of the N atoms ordering in Ta₂N compounds on their properties, the stability, elastic, and electronic properties of Ta₂N compounds (Ta₂N-I: P

\bar{3}

ml and Ta₂N-II: P [...] Read more.

Owing to exploring the influence of the N atoms ordering in Ta₂N compounds on their properties, the stability, elastic, and electronic properties of Ta₂N compounds (Ta₂N-I: P

\bar{3}

ml and Ta₂N-II: P

\bar{3}

1m) were investigated using first-principles calculations based on density functional theory. Ta₂N-II is energetically favorable according to the enthalpy of formation. Elastic constants were employed to reveal the stronger resistance to deformation, but weaker anisotropy, in Ta₂N-II. A ductile-brittle transition was found between Ta₂N-I (ductile) and Ta₂N-II (brittle). The partial density of states showed a stronger orbital hybridization of Ta-d and N-p in Ta₂N-II, resulting in stronger covalent bonding. The charge density difference illustrated the interaction of the Ta-N bond and electron distribution of Ta₂N. Full article

(This article belongs to the Special Issue Disordered Crystalline Materials)

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27 pages, 7767 KiB

Open AccessArticle

Preparation and Investigation of Pd and Bimetallic Pd-Sn Nanocrystals on γ-Al₂O₃

by Ivan Bondarchuk, Francisco José Cadete Santos Aires, Grigoriy Mamontov and Irina Kurzina

Crystals 2021, 11(4), 444; https://doi.org/10.3390/cryst11040444 - 19 Apr 2021

Cited by 7 | Viewed by 3484

Abstract

One of the key factors for producing highly dispersed controlled nanoparticles is the method used for metal deposition. The decomposition of metal-organic precursors is a good method for deposition of metal nanoparticles with very small sizes and narrow size distributions on the surface [...] Read more.

One of the key factors for producing highly dispersed controlled nanoparticles is the method used for metal deposition. The decomposition of metal-organic precursors is a good method for deposition of metal nanoparticles with very small sizes and narrow size distributions on the surface of various supports. The preparation process of Pd and bimetallic Pd-Sn nanoparticles supported onto γ-Al₂O₃ is considered. The samples were prepared by diffusional co-impregnation of the γ-Al₂O₃ support by using organometallic Pd(acac)₂ and Sn(acac)₂Cl₂ precursors. To achieve the formation of Pd and bimetallic Pd-Sn nanoparticles on the support surface, the synthesized samples were then subjected to thermal decomposition under Ar (to decompose the organometallic bound to the surface while keeping the formed nanoparticles small) followed by an oxidation in O₂ (to eliminate the organic compounds remaining on the surface) and a reduction in H₂ (to reduce the nanoparticles oxidized during the previous step). A combination of methods (ICP-OES, TPR-H₂, XPS, TEM/EDX) was used to compare the physical-chemical properties of the synthesized Pd and bimetallic Pd-Sn nanoparticles supported on the γ-Al₂O₃. The three samples exhibit narrow size distribution with a majority on nanoparticles between 3 and 5 nm. Local EDX measurements clearly showed that the nanoparticles are bimetallic with the expected chemical composition and the measured global composition by ICP-OES. The surface composition and electronic properties of Pd and Sn on the γ-Al₂O₃ support were investigated by XPS, in particular the chemical state of palladium and tin after each step of thermal decomposition treatments (oxidation, reduction) by the XPS method has been carried out. The reducibility of the prepared bimetallic nanoparticles was measured by hydrogen temperature programmed reduction (TPR-H₂). The temperature programmed reduction TPR-H₂ experiments have confirmed the existence of strong surface interactions between Pd and Sn, as evidenced by hydrogen spillover of Pd to Sn (Pd-assisted reduction of oxygen precovered Sn). These results lead us to propose a mechanism for the formation of the bimetallic nanoparticles. Full article

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13 pages, 2327 KiB

Open AccessArticle

Oxidation of Cr(III) to Cr(VI) and Production of Mn(II) by Synthetic Manganese(IV) Oxide

by Kaiyin Chen, Lauren Bocknek and Bruce Manning

Crystals 2021, 11(4), 443; https://doi.org/10.3390/cryst11040443 - 19 Apr 2021

Cited by 15 | Viewed by 3801

Abstract

The heterogeneous oxidation of Cr(III) to Cr(VI), a toxic inorganic anion, by a synthetic birnessite (δ-MnO₂) was investigated in batch reactions using a combination of analytical techniques including UV–Vis spectrophotometry, microwave plasma–atomic emission spectrometry, X-ray diffraction (XRD), X-ray photoelectron [...] Read more.

The heterogeneous oxidation of Cr(III) to Cr(VI), a toxic inorganic anion, by a synthetic birnessite (δ-MnO₂) was investigated in batch reactions using a combination of analytical techniques including UV–Vis spectrophotometry, microwave plasma–atomic emission spectrometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), to evaluate both the solution speciation of Cr(III)/Cr(VI) and the surface of the reacted δ-MnO₂. The formation of dissolved Mn(II) was determined during the batch reactions to evaluate the extent and stoichiometry of the Cr(III) oxidation reaction. A stoichiometric 3:2 Mn(II):Cr(VI) molar relationship was observed in the reaction products. The reductive dissolution of the δ-MnO₂ by Cr(III) resulted in a surface alteration from the conversion of Mn(IV) oxide to reduced Mn(II) and Mn(III) hydroxides. The results of this investigation show that naturally occurring Cr(III) will readily oxidize to Cr(VI) when it comes in contact with MnO_2, forming a highly mobile and toxic groundwater contaminant. Full article

(This article belongs to the Special Issue Sustainable Composites with Solid Waste Materials)

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26 pages, 1483 KiB

Open AccessArticle

Application of General Full Factorial Statistical Experimental Design’s Approach for the Development of Sustainable Clay-Based Ceramics Incorporated with Malaysia’s Electric Arc Furnace Steel Slag Waste

by Pao Ter Teo, Siti Koriah Zakaria, Nurulakmal Mohd Sharif, Anasyida Abu Seman, Mustaffa Ali Azhar Taib, Julie Juliewatty Mohamed, Mahani Yusoff, Abdul Hafidz Yusoff, Mardawani Mohamad, Arlina Ali and Mohamad Najmi Masri

Crystals 2021, 11(4), 442; https://doi.org/10.3390/cryst11040442 - 19 Apr 2021

Cited by 15 | Viewed by 3258

Abstract

This study aims to optimize the composition (body formulation) and firing temperature of sustainable ceramic clay-based ceramics incorporated with electric arc furnace (EAF) steel slag waste using general full factorial design (GFFD). The optimization is necessary to minimize drawbacks of high iron oxide’s [...] Read more.

This study aims to optimize the composition (body formulation) and firing temperature of sustainable ceramic clay-based ceramics incorporated with electric arc furnace (EAF) steel slag waste using general full factorial design (GFFD). The optimization is necessary to minimize drawbacks of high iron oxide’s fluxing agent (originated from electric arc furnace, EAF steel slag waste), which led to severe surface defects and high closed porosity issue of the ceramics. Statistical analysis of GFFD including model adequacy checking, analysis of variance (ANOVA), interaction plots, regression model, contour plot and response optimizer were conducted in the study. The responses (final properties of ceramics) investigated were firing shrinkage, water absorption, apparent porosity, bulk density and modulus of rupture (MOR). Meanwhile, the factors employed in experimental parameters were weight percentage (wt.%) of EAF slag added and firing temperature. Upon statistical analysis, GFFD has deduced that wt.% amount of EAF slag added and firing temperatures are proven to significantly influence the final properties of the clay-based ceramic incorporated with EAF slag. The results of conducted statistical analysis were also highly significant and proven valid for the ceramics. Optimized properties (maximum MOR, minimum water absorption and apparent porosity) of the ceramic were attained at 50 wt.% of EAF slag added and firing temperature of 1180 °C. Full article

(This article belongs to the Special Issue Recycling Silicate-Bearing Waste Materials)

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21 pages, 8504 KiB

Open AccessArticle

Study on Creep Damage in Sn₆₀Pb₄₀ and Sn_3.8Ag_0.7Cu (Lead-Free) Solders in c-Si Solar PV Cell Interconnections under In-Situ Thermal Cycling in Ghana

by Frank Kwabena Afriyie Nyarko, Gabriel Takyi and Francis Boafo Effah

Crystals 2021, 11(4), 441; https://doi.org/10.3390/cryst11040441 - 19 Apr 2021

Cited by 2 | Viewed by 2509

Abstract

A numerical study on the creep damage in soldered interconnects in c-Si solar photovoltaic cells has been conducted using equivalent creep strain, accumulated creep strain and accumulated creep energy density methods. The study used data from outdoor weathering of photovoltaic (PV) modules over [...] Read more.

A numerical study on the creep damage in soldered interconnects in c-Si solar photovoltaic cells has been conducted using equivalent creep strain, accumulated creep strain and accumulated creep energy density methods. The study used data from outdoor weathering of photovoltaic (PV) modules over a three-year period (2012–2014) to produce temperature cycle profiles that served as thermal loads and boundary conditions for the investigation of the soldered interconnects’ thermo-mechanical response when exposed to real-world conditions. A test region average (TRA) temperature cycle determined in a previous study for the 2012–2014 data was also used. The appropriate constitutive models of constituent materials forming a typical solar cell were utilized to generate accurate material responses to evaluate the damage from the thermal cycles. This study modeled two forms of soldered interconnections: Sn60Pb40 (SnPb) and Sn3.8Ag0.7Cu (Pb-free). The results of the damage analysis of the interconnections generated from the thermal cycle loads using accumulated creep strain method showed that the Pb-free solder interconnection recorded greater damage than that of the SnPb-solder interconnection for the TRA, 2012, 2013 and 2014 temperature cycles. The percentage changes from SnPb to Pb-free were 57.96%, 43.61%, 44.87% and 45.43%, respectively. This shows significant damage to the Pb-free solder under the TRA conditions. Results from the accumulated creep energy density (ACED) method showed a percentage change of 71.4% (from 1.3573 × 10⁵ J/mm³ to 2.3275 × 10⁵ J/mm³) in accumulated creep energy density by replacing SnPb-solder with Pb-free solder interconnection during the TRA thermal cycle. At the KNUST test site in Kumasi, Ghana, the findings show that Sn60Pb40 solder interconnections are likely to be more reliable than Pb-free solder interconnections. The systematic technique employed in this study would be useful to the thermo-mechanical reliability research community. The study also provides useful information to PV design and manufacturing engineers for the design of robust PV modules. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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13 pages, 5531 KiB

Open AccessArticle

High-Efficiency Responsive Smart Windows Fabricated by Carbon Nanotubes Modified by Liquid Crystalline Polymers

by Yuan Deng, Shi-Qin Li, Qian Yang, Zhi-Wang Luo and He-Lou Xie

Crystals 2021, 11(4), 440; https://doi.org/10.3390/cryst11040440 - 18 Apr 2021

Cited by 10 | Viewed by 2930

Abstract

Smart windows can dynamically and adaptively adjust the light transmittance in non-energy or low-energy ways to maintain a comfortable ambient temperature, which are conducive to efficient use of energy. This work proposes a liquid crystal (LC) smart window with highly efficient near-infrared (NIR) [...] Read more.

Smart windows can dynamically and adaptively adjust the light transmittance in non-energy or low-energy ways to maintain a comfortable ambient temperature, which are conducive to efficient use of energy. This work proposes a liquid crystal (LC) smart window with highly efficient near-infrared (NIR) response using carbon nanotubes grafted by biphenyl LC polymer brush (CNT-PDB) as the orientation layer. The resultant CNT-PDB polymer brush can provide the vertical orientation of LC molecules to maintain the initial transparency. At the same time, the smart window shows a rapid response to NIR light, which can quickly adjust the light transmittance to prevent sunlight from entering the room. Different from common doping systems, this method avoids the problem of poor compatibility between the LC host and photothermal conversion materials, which is beneficial for improving the durability of the device. Full article

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

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15 pages, 2935 KiB

Open AccessReview

Sol–Gel Ceramics for SEIRAS and SERS Substrates

by Jesús Alberto Garibay’Alvarado and Simón Yobanny Reyes-López

Crystals 2021, 11(4), 439; https://doi.org/10.3390/cryst11040439 - 18 Apr 2021

Cited by 7 | Viewed by 3806

Abstract

Surface Enhanced Infrared Absorption Spectroscopy and Surface Enhanced Raman Spectroscopy are analytic techniques that have not been massively adopted since there are issues that still need to be solved with regard to the nature of the signal enhancement substrates used. The sol–gel method [...] Read more.

Surface Enhanced Infrared Absorption Spectroscopy and Surface Enhanced Raman Spectroscopy are analytic techniques that have not been massively adopted since there are issues that still need to be solved with regard to the nature of the signal enhancement substrates used. The sol–gel method for the obtention of ceramics provides an alternative for the production of said substrates. Ceramics are very wear- and heat-resistant, properties that can be used for their regeneration, and through the sol–gel method, ceramics can be produced with high purity as well as can be fashioned in many ways through different techniques, which can be helpful in the pursuit of reproducibility. This paper discusses the different advantages of sol–gel ceramics, their use in the electrospinning technique, and their application in infrared and Raman surface-enhanced spectroscopy. 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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12 pages, 4872 KiB

Open AccessArticle

The Influence of Silicateins on the Shape and Crystalline Habit of Silica Carbonate Biomorphs of Alkaline Earth Metals (Ca, Ba, Sr)

by Nuria Sánchez-Puig, Mayra Cuéllar-Cruz, Selene R. Islas, Juana V. Tapia-Vieyra, Roberto A. Arreguín-Espinosa and Abel Moreno

Crystals 2021, 11(4), 438; https://doi.org/10.3390/cryst11040438 - 17 Apr 2021

Cited by 5 | Viewed by 2577

Abstract

This contribution presents the effect of two ortholog enzymes from marine sponges called silicateins on the formation of silica carbonate biomorphs of alkaline metals (Ca, Ba, Sr). In vivo, these enzymes participate in the polymerization of silica. Silicateins from Tethya aurantia and Suberitis [...] Read more.

This contribution presents the effect of two ortholog enzymes from marine sponges called silicateins on the formation of silica carbonate biomorphs of alkaline metals (Ca, Ba, Sr). In vivo, these enzymes participate in the polymerization of silica. Silicateins from Tethya aurantia and Suberitis domuncula were produced recombinantly and presented different degrees of activity, as evidenced by their ability to cleave silyl ether-like bonds in a model compound. Biomorphs are typically inorganic structures that show characteristic shapes resembling those of biological structures such as helices, leaves, flowers, disks or spheres. Irrespective of the concentration or the enzyme used, the presence of silicateins inhibited the formation of classic morphologies of biomorphs, albeit to different extents. Thus, not only the silica condensation activity of the enzyme but also its ability to bind silica compounds is implicated in the inhibition process. The largest effect was observed for the strontium and barium biomorphs, leading to the formation of spheres similar to those observed in diatoms and Radiolaria rather than the classical non-symmetrical forms. Characterization of the samples using Raman spectroscopy showed that silicatein did not affect the crystalline structure of the alkaline earth metal carbonate but did modify the crystalline habit. Full article

(This article belongs to the Special Issue Advanced Methods to Monitor and Control the Crystallisation Environment)

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14 pages, 6380 KiB

Open AccessArticle

Nucleation and Post-Nucleation Growth in Diffusion-Controlled and Hydrodynamic Theory of Solidification

by Frigyes Podmaniczky and László Gránásy

Crystals 2021, 11(4), 437; https://doi.org/10.3390/cryst11040437 - 17 Apr 2021

Cited by 5 | Viewed by 3166

Abstract

Two-step nucleation and subsequent growth processes were investigated in the framework of the single mode phase-field crystal model combined with diffusive dynamics (corresponding to colloid suspensions) and hydrodynamical density relaxation (simple liquids). It is found that independently of dynamics, nucleation starts with the [...] Read more.

Two-step nucleation and subsequent growth processes were investigated in the framework of the single mode phase-field crystal model combined with diffusive dynamics (corresponding to colloid suspensions) and hydrodynamical density relaxation (simple liquids). It is found that independently of dynamics, nucleation starts with the formation of solid precursor clusters that consist of domains with noncrystalline ordering (ringlike projections are seen from certain angles), and regions that have amorphous structure. Using the average bond order parameter

{\bar{q}}_{6}

, we distinguished amorphous, medium range crystallike order (MRCO), and crystalline local orders. We show that crystallization to the stable body-centered cubic phase is preceded by the formation of a mixture of amorphous and MRCO structures. We have determined the time dependence of the phase composition of the forming solid state. We also investigated the time/size dependence of the growth rate for solidification. The bond order analysis indicates similar structural transitions during solidification in the case of diffusive and hydrodynamic density relaxation. Full article

(This article belongs to the Special Issue Modeling of Crystal Growth)

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13 pages, 3096 KiB

Open AccessArticle

Standardized Procedure of Measuring the pH Value of Cement Matrix Material by Ex-Situ Leaching Method (ESL)

by Wei-Chien Wang, Wei-Hsing Huang, Ming-Yu Lee, Hoang Trung Hieu Duong and Ya-Hui Chang

Crystals 2021, 11(4), 436; https://doi.org/10.3390/cryst11040436 - 17 Apr 2021

Cited by 13 | Viewed by 3713

Abstract

According to the Spanish National Research Council (CSIC) report, the ex-situ leaching method (ESL) is more appropriate and accurate than other methods for measuring pH value in terms of repeatability and reproducibility. In this study, the ESL method was used to measure the [...] Read more.

According to the Spanish National Research Council (CSIC) report, the ex-situ leaching method (ESL) is more appropriate and accurate than other methods for measuring pH value in terms of repeatability and reproducibility. In this study, the ESL method was used to measure the pH value of cement matrix materials. The design test process aimed to avoid underestimating the variation in pH during the process of solution stirring and pH measurement without using both argon and nitrogen to block the specimen contact with air, with good repeatability and reproducibility. This study also considered the influence of the dryness of the specimen before crushing, the size of the powder, the air-exposed specimen, the air-exposed solution, the temperature of the solution, etc. After testing and analysis, a standard procedure for detecting the pH value of cement matrix materials was established which is known as the S-ESL method. Full article

(This article belongs to the Special Issue Advances in Cement-Based Composites and Novel Construction Products)

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34 pages, 19724 KiB

Open AccessReview

Crystal Plasticity Simulation of Magnesium and Its Alloys: A Review of Recent Advances

by Mohammadreza Yaghoobi, George Z. Voyiadjis and Veera Sundararaghavan

Crystals 2021, 11(4), 435; https://doi.org/10.3390/cryst11040435 - 17 Apr 2021

Cited by 29 | Viewed by 4886

Abstract

Slip and extension twinning are the dominant deformation mechanisms in Magnesium (Mg) and its alloys. Crystal plasticity is a powerful tool to study these deformation mechanisms. Different schemes have incorporated crystal plasticity models to capture different properties, which vary from the simple homogenization [...] Read more.

Slip and extension twinning are the dominant deformation mechanisms in Magnesium (Mg) and its alloys. Crystal plasticity is a powerful tool to study these deformation mechanisms. Different schemes have incorporated crystal plasticity models to capture different properties, which vary from the simple homogenization Taylor model to the full-scale crystal plasticity finite element model. In the current study, a review of works available in the literature that addresses different properties of Mg and its alloys using crystal plasticity modes is presented. In addition to slip and twinning, detwinning is another deformation mechanism that is activated in Mg and its alloys. The different models that capture detwinning will also be addressed here. Finally, the recent experimental frameworks, such as in-situ neutron diffraction, 3D high energy synchrotron X-ray techniques, and digital image correlation under scanning electron microscopy (SEM-DIC), which are incorporated along crystal plasticity models to investigate the properties of Mg and its alloys, are addressed. Future research directions towards improving the deformation response of Mg and its alloys are identified, which can lead to increased deployment of the lightest structural metal in engineering applications. Full article

(This article belongs to the Special Issue Applications of Crystal Plasticity in Forming Technologies)

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11 pages, 33997 KiB

Open AccessArticle

The Modulating Effect of Ethanol on the Morphology of a Zr-Based Metal–Organic Framework at Room Temperature in a Cosolvent System

by Yunzhuo Li, Zirong Tang and Chen Chen

Crystals 2021, 11(4), 434; https://doi.org/10.3390/cryst11040434 - 16 Apr 2021

Cited by 9 | Viewed by 3598

Abstract

We report that ethanol, used together with water, plays a crucial role in tuning the structures of a zirconium-based metal–organic framework and the 12-connected MOF-801, as well as the possible mechanisms of this modulating effect. By employing a cosolvent system of ethanol and [...] Read more.

We report that ethanol, used together with water, plays a crucial role in tuning the structures of a zirconium-based metal–organic framework and the 12-connected MOF-801, as well as the possible mechanisms of this modulating effect. By employing a cosolvent system of ethanol and water at just under room temperature without the presence of a monotopic carboxylic acid as the modulator, MOF-801 in various morphologies of different sizes could be synthesized. A linear correlation between the ethanol/water ratio and the crystal sizes is also demonstrated. The growth mechanism is mainly explained by ethanol’s bonding with the metal ion clusters and the Marangoni flow effect. Ethanol competes with the linker molecules in coordinating with the Zr metal clusters, a role similar to that of the modulators. The Marangoni flow effect, which dominates at a certain solvent ratio, further promotes the 1D alignment of the MOF-801 crystals. Full article

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20 pages, 3413 KiB

Open AccessReview

Characterising Supramolecular Architectures in Crystals Featuring I⋯Br Halogen Bonding: Persistence of X⋯X’ Secondary-Bonding in Their Congeners

by Edward R. T. Tiekink

Crystals 2021, 11(4), 433; https://doi.org/10.3390/cryst11040433 - 16 Apr 2021

Cited by 9 | Viewed by 2212

Abstract

The Cambridge Structural Database was surveyed for crystals featuring I⋯Br secondary-bonding in their supramolecular assemblies occurring independently of other obvious supramolecular synthons and devoid of other halogen bonding interactions. In all, 41 crystals satisfied these criteria, with nine examples of zero-dimensional aggregation (uniformly [...] Read more.

The Cambridge Structural Database was surveyed for crystals featuring I⋯Br secondary-bonding in their supramolecular assemblies occurring independently of other obvious supramolecular synthons and devoid of other halogen bonding interactions. In all, 41 crystals satisfied these criteria, with nine examples of zero-dimensional aggregation (uniformly two-molecule aggregates) and 30 one-dimensional chains of varying topology (linear, zigzag and helical). There is one example each of two- and three-dimensional patterns. Type-I, type-II and intermediate bonding situations are apparent; for type-II bonding, the ratio of iodide:bromide functioning as the electrophile is 2:1. Most molecules participated, on average, in one I⋯Br contact, although smaller numbers of half (zero-dimensional) or two contacts (two- and three-dimensional) were observed. The propensity of the formation of related halogen bonding interactions in congeners of the 41 investigated crystals was also studied. Congeners were apparent for 11 crystals, with seven of these exhibiting isostructural relationships, in terms of space-group symmetry and unit-cell parameters. Isostructural relationships do not ensure the formation of analogous aggregation patterns, particularly and in accord with expectation, for the lighter halides. When formed, often distinct aggregation patterns are observed despite the isostructural relationships. Hetero-atomic halogen bonding offers surprises and opportunities in crystal engineering endeavours. Full article

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

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14 pages, 2660 KiB

Open AccessArticle

The Prediction of the Undercooling Degree of As-Cast Irons and Aluminum Alloys via Machine Learning

by Yong Chen, Litao Wen, Shuncheng Wang, Zhibo Zhang, Cuicui Yin, Nan Zhou and Kaihong Zheng

Crystals 2021, 11(4), 432; https://doi.org/10.3390/cryst11040432 - 16 Apr 2021

Cited by 2 | Viewed by 2185

Abstract

As-cast irons and aluminum alloys are used in various industrial fields and their phase and microstructure properties are strongly affected by the undercooling degree. However, existing studies regarding the undercooling degree are mostly limited to qualitative analyses. In this paper, a quantitative analysis [...] Read more.

As-cast irons and aluminum alloys are used in various industrial fields and their phase and microstructure properties are strongly affected by the undercooling degree. However, existing studies regarding the undercooling degree are mostly limited to qualitative analyses. In this paper, a quantitative analysis of the undercooling degree is performed by collecting experimental data and employing machine learning. Nine machining learning models including Random Forest (RF), eXtreme Gradient Boosting (XGBOOST), Ridge Regression (RIDGE) and Gradient Boosting Regressor (GBDT) methods are used to predict the undercooling degree via six features, which include the cooling rate (CR), mean atomic covalence radius (MAR) and mismatch (MM). Four additional effective models of machine learning algorithms are then selected for a further analysis and cross-validation. Finally, the optimal machine learning model is selected for the dataset and the best combination of features is found by comparing the prediction accuracy of all possible feature combinations. It is found that RF model with CR and MAR features has the optimal performance results for predicting the undercooling degree. Full article

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13 pages, 3121 KiB

Open AccessEditor’s ChoiceArticle

Extraction–Pyrolytic Method for TiO₂ Polymorphs Production

by Vera Serga, Regina Burve, Aija Krumina, Marina Romanova, Eugene A. Kotomin and Anatoli I. Popov

Crystals 2021, 11(4), 431; https://doi.org/10.3390/cryst11040431 - 16 Apr 2021

Cited by 50 | Viewed by 3976

Abstract

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO₂) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) [...] Read more.

The unique properties and numerous applications of nanocrystalline titanium dioxide (TiO₂) are stimulating research on improving the existing and developing new titanium dioxide synthesis methods. In this work, we demonstrate for the first time the possibilities of the extraction–pyrolytic method (EPM) for the production of nanocrystalline TiO₂ powders. A titanium-containing precursor (extract) was prepared by liquid–liquid extraction using valeric acid C₄H₉COOH without diluent as an extractant. Simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA–DSC), as well as the Fourier-transform infrared (FTIR) spectroscopy were used to determine the temperature conditions to fabricate TiO₂ powders free of organic impurities. The produced materials were also characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The results showed the possibility of the fabrication of storage-stable liquid titanium (IV)-containing precursor, which provided nanocrystalline TiO₂ powders. It was established that the EPM permits the production of both monophase (anatase polymorph or rutile polymorph) and biphase (mixed anatase–rutile polymorphs), impurity-free nanocrystalline TiO₂ powders. For comparison, TiO₂ powders were also produced by the precipitation method. The results presented in this study could serve as a solid basis for further developing the EPM for the cheap and simple production of nanocrystalline TiO₂-based materials in the form of doped nanocrystalline powders, thin films, and composite materials. Full article

(This article belongs to the Special Issue Advances in Functional Inorganic Materials Prepared by Wet Chemical Methods)

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13 pages, 4073 KiB

Open AccessArticle

Observation of Backflow during the Anihilation of Topologocal Defects in Freely Suspended Smectic Films

by Amine Missaoui, Emmanuelle Lacaze, Alexey Eremin and Ralf Stannarius

Crystals 2021, 11(4), 430; https://doi.org/10.3390/cryst11040430 - 16 Apr 2021

Cited by 6 | Viewed by 2597

Abstract

Freely suspended films in the smectic C phase are excellent templates for the study of topological defect dynamics. It is well known that, during the annihilation of a pair of disclinations with strengths +/−1, the +1 defect moves faster because it is carried [...] Read more.

Freely suspended films in the smectic C phase are excellent templates for the study of topological defect dynamics. It is well known that, during the annihilation of a pair of disclinations with strengths +/−1, the +1 defect moves faster because it is carried towards its opponent by backflow, whereas the flow in the vicinity of the −1 defect is negligibly small. This backflow pattern is created by the defect motion itself. An experimental confirmation of this theoretical prediction and its quantitative characterization is achieved here by fluorescence labeling. Film regions near the defect positions are labeled and their displacements are tracked optically. Full article

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

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12 pages, 3205 KiB

Open AccessArticle

Interfacial Bonding and Mechanical Properties of Al/Mg Dissimilar Refill Friction Stir Spot Welds Using a Grooved Tool

by Zhikang Shen, Xinyu Liu, Dongxiao Li, Yuquan Ding, Wentao Hou, Haiyan Chen, Wenya Li and Adrian P. Gerlich

Crystals 2021, 11(4), 429; https://doi.org/10.3390/cryst11040429 - 16 Apr 2021

Cited by 6 | Viewed by 2463

Abstract

Al/Mg dissimilar welds were successfully fabricated by refill friction stir spot welding using a grooved sleeve tool. Influences of sleeve penetration depth and rotational speed on the weld formation and mechanical performance were systematically evaluated in terms of welding parameter optimization, interfacial bonding [...] Read more.

Al/Mg dissimilar welds were successfully fabricated by refill friction stir spot welding using a grooved sleeve tool. Influences of sleeve penetration depth and rotational speed on the weld formation and mechanical performance were systematically evaluated in terms of welding parameter optimization, interfacial bonding mechanism, hardness distribution and welded joint strength. The results indicated that the success of joining Al alloy to Mg alloy significantly depends on tool sleeve penetration depth. The interfacial bonding mechanism compromised both metallurgical bonding and mechanical inter-locking. Intermetallic compound layers of Al₃Mg₂ and Al₁₂Mg₁₇ were formed at the Al/Mg interface. The thickness of the intermetallic compound (IMC) layer at the weld center increased from 20–30 μm to 40 μm when the rotational speed increased from 1000 to 2000 rpm. The minimum hardness was 80 HV in Al 7075 and 52 HV in ZEK 100; both were measured in the heat affected zone. The welded joint lap shear strength decreased, and the scatter increased with the increasing of rotation speed, whose maximum was 3.6 kN when the rotational speed was 1000 rpm. In addition, the failure mechanism was determined by tool rotational speed, and found to be interfacial failure under a rotational speed of 1000 rpm and nugget pullout under a rotational speed of 2000 rpm. Full article

(This article belongs to the Special Issue Interface at Dissimilar Crystal Structures)

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8 pages, 1518 KiB

Open AccessArticle

Fractional Power-Law Intraband Optical Conductivity in the Low-Dimensional Dirac Material CaMnBi₂

by M. B. Schilling, C. X. Wang, Y. G. Shi, R. K. Kremer, M. Dressel and A. V. Pronin

Crystals 2021, 11(4), 428; https://doi.org/10.3390/cryst11040428 - 16 Apr 2021

Cited by 3 | Viewed by 2492

Abstract

We studied the broadband optical conductivity of CaMnBi₂, a material with two-dimensional Dirac electronic bands, and found that both components of the intraband conductivity follow a universal power law as a function of frequency at low temperatures. This conductivity scaling differs [...] Read more.

We studied the broadband optical conductivity of CaMnBi₂, a material with two-dimensional Dirac electronic bands, and found that both components of the intraband conductivity follow a universal power law as a function of frequency at low temperatures. This conductivity scaling differs from the Drude(-like) behavior, generally expected for free carriers, but matches the predictions for the intraband response of an electronic system in a quantum critical region. Since no other indications of quantum criticality are reported for CaMnBi₂ so far, the cause of the observed unusual scaling remains an open question. Full article

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

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17 pages, 5676 KiB

Open AccessArticle

Comparative Study of High-Performance Concrete Characteristics and Loading Test of Pretensioned Experimental Beams

by Pavlina Mateckova, Vlastimil Bilek and Oldrich Sucharda

Crystals 2021, 11(4), 427; https://doi.org/10.3390/cryst11040427 - 15 Apr 2021

Cited by 20 | Viewed by 2997

Abstract

High-performance concrete (HPC) is subjected to wide attention in current research. Many research tasks are focused on laboratory testing of concrete mechanical properties with specific raw materials, where a mixture is prepared in a relatively small amount in ideal conditions. The wider utilization [...] Read more.

High-performance concrete (HPC) is subjected to wide attention in current research. Many research tasks are focused on laboratory testing of concrete mechanical properties with specific raw materials, where a mixture is prepared in a relatively small amount in ideal conditions. The wider utilization of HPC is connected, among other things, with its utilization in the construction industry. The paper presents two variants of HPC which were developed by modification of ordinary concrete used by a precast company for pretensioned bridge beams. The presented variants were produced in industrial conditions using common raw materials. Testing and comparison of basic mechanical properties are complemented with specialized tests of the resistance to chloride penetration. Tentative expenses for normal strength concrete (NSC) and HPC are compared. The research program was accomplished with a loading test of model experimental pretensioned beams with a length of 7 m made of ordinarily used concrete and one variant of HPC. The aim of the loading test was to determine the load–deformation diagrams and verify the design code load capacity calculation method. Overall, the article summarizes the possible benefits of using HPC compared to conventional concrete. Full article

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

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10 pages, 3703 KiB

Open AccessArticle

Improving the Ionic Conductivity of the LLZO–LZO Thin Film through Indium Doping

by Zongkai Yan, Yu Song, Shuai Wu, Yongmin Wu, Shipai Song, Xinyu Wang, Yanlin Zhu, Junsong Chen, Rui Guo and Yong Xiang

Crystals 2021, 11(4), 426; https://doi.org/10.3390/cryst11040426 - 15 Apr 2021

Cited by 5 | Viewed by 5262

Abstract

A solid-state electrolyte with an ionic conductivity comparable to that of a liquid electrolyte is demanded of all-solid-state lithium-ion batteries. Li₇La₃Zr₂O₁₂ (LLZO) is considered to be a promising candidate due to its good thermal stability, high [...] Read more.

A solid-state electrolyte with an ionic conductivity comparable to that of a liquid electrolyte is demanded of all-solid-state lithium-ion batteries. Li₇La₃Zr₂O₁₂ (LLZO) is considered to be a promising candidate due to its good thermal stability, high ionic conductivity, and wide electrochemical window. However, the synthesis of a stable cubic-phase LLZO thin film with enhanced densification at a relatively low thermal treatment temperature is yet to be developed. Indium is predicted to be a possible dopant to stabilize the cubic-phase LLZO (c-LLZO). Herein, via a nanolayer stacking process, a LLZO–Li₂CO₃–In₂O₃ multilayer solid electrolyte precursor was obtained. After thermal annealing at different temperatures, the effects of indium doping on the formation of c-LLZO and the ionic conductivities of the prepared LLZO–LZO thin film were systematically investigated. The highest ionic conductivity of 9.6 × 10⁻⁶ S·cm^–1 was obtained at an annealing temperature of 800 °C because the incorporation of indium promoted the formation of c-LLZO and the highly conductive LLZO–LZO interfaces. At the end, a model of LLZO–LZO interface-enhancing ionic conductivity was proposed. This work provides a new approach for the development of low-temperature LLZO-based, solid-state thin-film batteries. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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