Crystals, Volume 13, Issue 3 (March 2023) – 182 articles

In our previous work, we obtained the uniformly valid asymptotic solution of a cylindrical rod eutectic. In order to further study the critical point of the stable growth of a rod eutectic, we have considered the unsteady growth of a rod eutectic on the basis of the steady solution of the rod eutectic. Based on the experimental system of rod eutectic growth, combined with solidification thermodynamics and kinetics, the unsteady mathematical model of the rod eutectic was established. We used the asymptotic analysis method to seek the analytical solution of the mathematical model and used the nonlinear stability analysis theory to analyze the analytical solution and establish the corresponding disturbance model. We obtained the analytic form of the global mode solution and the corresponding quantization conditions and find that there is a stable growth mode, namely the mode (ST-mode), for rod eutectic growth; when $\epsilon <{\epsilon }_{\mathrm{S}\mathrm{T}}^0$, the rod eutectic growth is stable, when $\epsilon >{\epsilon }_{\mathrm{S}\mathrm{T}}^0$, the rod eutectic growth is unstable and when $\epsilon ={\epsilon }_{\mathrm{S}\mathrm{T}}^0$, the rod eutectic growth is of a neutral stability. The critical eutectic spacing of succinonitrile(D)camphor (SCN-DC) predicted by us is smaller than that predicted by Jackson–Hunt, which is consistent with the corresponding experimental data. Finally, we found that the critical eutectic spacing and stable region of rod eutectic growth changed little with the temperature gradient. Full article

This paper describes a strategy for preparing free-standing reduced graphene oxide@Si nanoparticles (rGO@Si NPs) composite membranes. Graphene oxide (GO) was reduced and self-assembled synchronously with nanoparticles of silicon (Si NPs) on a metal surface and the composite film was subsequently used in a lithium-ion battery (LIB). This work describes several important novel aspects of the reported technology. Firstly, the composite membrane has a flexible self-supporting structure, allowing it to function as an anode material without requiring binders and current collectors. Secondly, the successful assembly of Si NPs and reduced Graphene oxide (rGO) sheets has enabled the production of the rGO@Si NPs composite film with high controllability and orderliness. Thirdly, the conductive nature of graphene has significantly decreased the resistivity while enhancing the electron transport capacity of the battery anode. Lastly, the robust and flexible structure of the graphene sheet has greatly mitigated the large volume variation in Si NPs during charging or discharging, resulting in the rGO@Si NPs composite film exhibiting excellent energy density and high-power density. Full article

Gas metal arc welding-based additive manufacturing (GMA–AM) is a promising, low-cost approach to fabricate large-scale and complex geometry components using layer-by-layer deposition of metals. However, the low forming accuracy of GMA–AM still limits its one-off industrial application due to the strong and nonlinear interactions between arc–droplet transfer and molten pool. To fully understand the influential mechanism of this inherent interaction in the GMA–AM process to precisely control the part accuracy, the arc–droplet transfer behavior in the GMA–AM process with different current waveforms was firstly studied experimentally. The phenomena of the arc swing and the differing droplet transfer with the increase in deposited height were interpreted. The thermal force status of the molten pool and its balance boundary conditions were also theoretically analyzed. Finally, the microstructure and the hardness of the AM parts with different cooling times were tested and analyzed. The experimental results demonstrate that using the spray droplet transfer mode can generate a stable AM process under direct current application conditions, but it easily ends the AM process at the third or fourth layer deposition owing to excessive heat input. A more highly accurate deposition morphology can be obtained in one droplet per pulse mode under pulsed current application conditions, which also indicates that the AM process with a constant current welding supply is stabler and easily produces better deposition than the process with a constant voltage welding supply. With the increase in cooling time, the microstructure evolved from fine ferrite to equiaxed ferrite and to columnar ferrite combined with acicular ferrite with a lower proportion of pearlite in the vertical direction of the part, and the average hardness changed to ~168 HV (bottom), ~175 HV (middle), and ~250 HV (top). The analysis indicates that the heat accumulation of the molten pool is a critical factor that affects the deposition accuracy. To this end, a novel strategy that uses the heat accumulation to compensate for the energy formed in the molten pool is proposed to further reduce the arc heat input and weaken the heat accumulation, and its feasibility is discussed. Full article

We theoretically investigate the optical bistability in superconductor–semiconductor photonic crystals composed of graphene. The photonic crystals are symmetric to the center and arranged alternately by the superconductor (HgBa₂Ca₂Cu₃O_8+δ) and semiconductor (GaAs) layers. The system supports a defect mode, and graphene is located at the layer interface where the local electric field is the strongest. Consequently, the optical nonlinearity of graphene has been greatly enhanced, and low-threshold optical bistability can be achieved with an incident wavelength red-detuning to the defect mode. The upper and lower thresholds of bistability increase with the increase in the value of low environmental temperature, while the interval between the upper and lower thresholds decreases. This research has a potential application in temperature-controlled optical switches and temperature-controlled optical memory. Full article

Cellular automata (CA) modeling is a powerful and efficient tool for simulating the dynamic evolution of polycrystalline microstructures in modern materials and metallurgy studies, such as solidification, plastic deformation and recrystallization. We propose a novel model to calculate the shape factor of grains in three-dimensional hexagonal grid (3D-HEX) CA, which overcomes the disadvantages of 3D-HEX CA, such as complex algorithms and a long computation time. The shape factor is a quantitative measure of grain morphology based on the ratio of the surface area of the grain to its volume-equivalent-sphere and volume-equivalent-chain. It indicates how the shape of a grain or phase affects its mechanical properties, such as stiffness, deformation and fracture. Our model can easily calculate the shape factor for any grain by counting its surface cells and volume cells. We test our model on 1000 grains with different shapes (equiaxed, irregular and chain-like) by Monte Carlo (MC) methods. MC methods evaluate the validity of a calculation model by comparing the simulated outcomes with the observed or expected outcomes. The results show that our model can accurately describe the grain morphology and has a good comparability and generality. Full article

Tri-metallic NiMoW catalysts prepared by impregnating mesoporous aluminas (pore sizes of ~9 nm and surface areas of ~225 m²/g) obtained by sol-gel (NiMoW/Al) and hydrothermal (NiMoW/Al_HYDT) processes were investigated in the hydrodesulfurization (HDS) of thiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT) at H₂ pressures of 1 MPa and 5.0 MPa, respectively. The supports and catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The NiMoW/Al_HYDT catalyst, which was the most active in both test HDS reactions, was characterized by a pore size of 7.5 nm, whereas the pore size of the catalyst on sol-gel alumina (NiMoW/Al) was only 4.8 nm. Moreover, the NiMoW/Al_HYDT catalyst exhibited reduction peaks shifted to a lower temperature during TPR, indicating weaker metal support interactions, a higher degree of Mo (79%) and W (48%) sulfidation, and an optimal layer slab length distribution of Mo(W)S₂ nanocrystals preferentially between 2–4 nm with an average layer stacking of 1.7 compared to the NiMoW/Al counterpart. Full article

The influence of residual heat on the fictive temperature modification zone of fused silica for different CO₂ laser scanning time intervals was investigated to precisely control the profiles of hydrofluoric (HF) acid-etched fused silica surface, which were formed by the increasing HF acid-etching rate for fused silica with increasing fictive temperature induced by CO₂ laser scanning. The surface profiles of HF acid-etched fused silica treated by different scanning time intervals of CO₂ laser were measured by a stylus profilometry, and experimental results indicate that the CO₂ laser scanning time intervals intensively influence the HF acid-etched surface profiles of fused silica. The increasing depth of surface profiles treated by shorter scanning time intervals shows that the fictive temperature modification zone significantly expands. Numerical simulations of the fictive temperature modification zone induced by different scanning time intervals indicate that the residual heat of CO₂ laser scanning with shorter time intervals leads to a dramatical increase in the fictive temperature modification zone. By adjusting the residual heat of CO₂ laser scanning intervals, various surface profiles of fused silica can be obtained by HF acid-etching of fused silica. Full article

In this investigation, pure aluminum (Al) powders were cryomilled with and without magnesium dopants to study (a) the effect of cryomilling time on the crystallite size and (b) the effect of magnesium dopant on Al to achieve grain boundary stability. The cryomilling process was carried out using liquid nitrogen for different durations. The characterization of the cryomilled powders was carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to understand the particle morphology, crystallite size, and elemental composition. The results demonstrated that the size of the crystallites in both Al and Mg-doped Al powders reduces as the cryomilling duration increases. The results also indicated that the preferential segregation of Mg dopant at the grain boundaries of Al provides stability to the cryomilled powders at elevated temperatures. This article discusses the mechanism for the changes in crystallite size and the effect of the Mg dopant on the grain boundary stability in Al powders. Full article

The local microstructure, texture gradient and mechanical properties through the shoulder dimension (10 mm) of upper and lower AA5182 aluminum sheets were investigated using electron backscatter diffraction (EBSD) and Vickers microhardness after friction stir spot welding (FSSW). Based on the microstructural features (mean grain size, grain boundary type and dynamic recrystallization (DRX)), the upper sheet was found to be mainly composed of the stir zone (SZ) and thermomechanically affected zone (TMAZ) due to the high deformation induced simultaneously by the tool rotation and the shoulder download force, while the SZ, TMAZ, heat-affected zone (HAZ) and base metal (BM) were detected in the lower sheet due to the limited effect of the shoulder on the lower sheet. The texture changes, due to the nature of the deformation, demonstrated a shear-type texture at the SZ to a plane strain compression deformation type texture at the TMAZ and then a recrystallization texture at the HAZ and BM. The microhardness gradually decreased with the increasing distance from the keyhole along the SZ, TMAZ and HAZ regions. Eventually, the microstructure and microhardness evolutions were correlated based on the Hall–Petch relationship. Full article

Microscale single-crystal copper is widely used in electronics, communications and other fields due to its excellent properties such as high ductility, high toughness and good conductivity. Therefore, it is particularly important to research its fatigue life. In order to explore the influence of size effect, loading frequency and shear strain on the main slip surface on the fatigue life of microscale single-crystal copper based on in situ fatigue experimental data of microscale single-crystal copper, this paper used a BP neural network algorithm to construct a single-crystal copper fatigue life prediction network model. The data set included 14 groups of training data, with 11 groups as training sets and 3 groups as testing sets. The input characteristics were length, width, height, loading frequency and shear strain of the main sliding plane of a microscale single-crystal copper sample. The output characteristic was the fatigue life of microscale single-crystal copper. After training, the mean square error (MSE) of the model was 0.03, the absolute value error (MAE) was 0.125, and the correlation coefficient (R²) was 0.93271, indicating that the BP neural network algorithm can effectively predict the fatigue life of microscale single-crystal copper and has good generalization ability. This model can not only save the experimental time of fatigue life measurement of micro-scale single-crystal copper, but also optimize the properties of the material by taking equidistant points in the range of characteristic parameters. Therefore, the current study demonstrates an applicable and efficient methodology to evaluate the fatigue life of microscale materials in industrial applications. Full article

The (001) plate-like BaTiO₃ piezoelectric micromaterials are synthesized by topochemical microcrystal conversion technique. BaTiO₃ plates with a length of 2~10 μm and thickness of 0.5~1.3 μm are obtained. The dependence of morphology on synthesis conditions is discussed in detail. The crystal symmetry and multiscale domain structures of BaTiO₃ plates are systematically investigated by various characterizations. X-ray diffraction (XRD) and Raman spectra analyses demonstrate the tetragonal symmetry of the (001) oriented BaTiO₃ plates at room temperature. The domain configurations of the micron BaTiO₃ are investigated with a polarized light microscope (PLM) and piezoresponse force microscopy (PFM). The single-crystal-like quality and uniformity are supported by PLM observations. More importantly, the classical 90° banded ferroelectric domains of ~125 nm width are observed for the first time in such BaTiO₃ plates. The domain features in the mesoscale BaTiO₃ plate are discussed and compared with its bulk counterparts. The results may provide insights into understanding and designing the mesoscale BaTiO₃ functional materials. Full article

Cylindrical ferromagnetic nanowires are of particular interest in nanomaterials science due to various manufacturing methods and a wide range of applications in nanotechnology, with special attention given to those with diameters less than the single domain limit. In the current study, the simulations of magnetic properties of isolated iron nanowires with a diameter of 5 nm and various aspect ratios, as well as two types of arrays of such nanowires (with hexagonal and square arrangement), were performed using atomistic spin model. In the case of a single nanowire, change of coercive field for different applied field directions with aspect ratio was discussed. It was shown that the evolution of the magnetization reversal mechanism from coherent rotation to domain wall propagation appears with increasing length of single nanowire. For the arrays of cylindrical nanostructures, it was revealed that different number of nearest neighbors for each nanostructure in square and hexagonal arrays have an influence on their magnetostatic interactions, which are the most significant for shortest interwire distances. The corresponding spin configurations during the remagnetization process showed the appearance of intermediate magnetization states (when a part of wires is magnetized parallel and part antiparallel to the field direction), connected with Barkhausen effect, which influence the observed hysteresis curves. Full article

The thermal treatment of electromechanically active thick films prepared by aerosol deposition (AD) is a common practice to improve their electrical and electromechanical properties. We report on how post-deposition annealing in air affects the unique cross-sectional microstructure and mechanical properties of 0.9Pb(Mg_1/3Nb_2/3)O₃−0.1PbTiO₃ thick films prepared by AD. Transmission electron microscopy revealed minor but detectable changes, such as pore redistribution and grain growth after annealing at 500 °C. We also showed that the stainless-steel substrate is strongly affected by the annealing. The hardness and Young’s modulus of the films increased after annealing, with both properties being discussed in terms of their distribution over the cross-sections of the films. Full article

Using N2O4 donor symmetric ligand H₂L and dca co-ligand, two new isostructural dinuclear Cu^II–Ln^III complexes [Cu(Cl)(L)Ln(NO₃)(CH₃OH)(H₂O)(dca)] [Ln=Ho (1_CuHo), Gd (2_CuGd)] [H₂L = 6,6′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol); dca=dicyanamide] were designed, synthesized and studied. In the two isostructural compounds, the geometric environment around the nine-coordinated Ln(III) ions is muffin, whereas the geometry of the penta-coordinated Cu(II) ions is square pyramid. The magnetic properties of both complexes were also studied. Direct current magnetic susceptibility measurements indicate ferromagnetic interactions between the Cu(II) ion and Gd(III) ion in complex 2_CuGd. Alternating current (ac) magnetic measurements indicate that complex 1_CuHo displays slow magnetic relaxation behaviour. Full article

The presented work shows the study of energy transitions in the NIR and visible regions in the system of Bi₂O₃ and Tm₂O₃ powders. Mechanisms of upconversion luminescence and NIR luminescence between two Bi³⁺ and Tm³⁺ ions at T = 80 K accompanied with nonradiative energy transfer through the vibrational levels were investigated under IR photoexcitation. The absorption bands of the samples on the reflection spectra were examined in the visible region. The values of the emission cross-section parameters were calculated for the Bi₂O₃/Tm₂O₃ complexes. Full article

ITO/Pt, In₂O₃/Pt and ITO/In₂O₃ thermocouples were prepared by the radio frequency (RF) magnetron sputtering method. The XRD results showed that all the annealed ITO and In₂O₃ films annealed at high temperature present a cubic structure. Scanning electron microscope results showed that the thickness of the ITO and In₂O₃ films could reach 1.25 µm and 1.21 µm, respectively. The ITO/Pt and In₂O₃/Pt thin film thermocouples could obtain an output voltage of 68.7 mV and 183.5 mV, respectively, under a 900 °C temperature difference, and at the same time, the Seebeck coefficient reached 76.1 µV/°C and 203.9 µV/°C, respectively. For the ITO/In₂O₃ thermocouple, the maximum value of the output voltage was 165.7 mV under a 1200 °C temperature difference, and the Seebeck coefficient was 138.1 µV/°C. Annealing under different atmosphere conditions under 1000 °C, including vacuum, air and nitrogen atmospheres, resulted in values of the Seebeck coefficient that were 138.2 µV/°C, 135.5 µV/°C and 115.7 µV/°C, respectively. Full article

This article presents results from a simple experimental methodology used to determine the amount of heat transferred from an yttrium barium copper oxide (YBCO) bulk to liquid nitrogen (LN2) and LN₂ consumption during the process of zero-field cooling (ZFC). The thermal power can be determined from the YBCO bulk temperature variation, which is difficult to measure with accuracy. In this procedure, the thermal power from the YBCO bulk to LN₂ is determined from the measured rate of LN₂ evaporation, considering the LN₂ latent heat. To reduce the influence of room temperature heating and make the LN2 mass variation depend as much as possible on the heat released from the YBCO bulk, a step transient from room temperature into the LN₂ is performed. The precision of results is determined from the rate of LN₂ evaporation due to room temperature heating with the bulk already cooled by ZFC. The temperature evolution at the bulk lateral surface where the heat transfer is higher is also measured. The results from experimental measurements are compared with 3D finite element analysis (FEA) numerical results. The obtained evolutions of the temperature and thermal power from the YBCO bulk are used to validate YBCO thermal parameters, such as thermal conductivity and specific heat capacity at constant pressure. The YBCO bulk equivalent heat capacity and thermal resistance are determined by analyzing the equivalent first-order thermal lumped parameter circuit based on the obtained evolutions in time of the YBCO temperature and heat transferred to the LN₂. The characteristics of dependence of the YBCO thermal resistance and heat capacity with temperature are obtained by correlating their time evolutions with the bulk average temperature evolution in time. The YBCO-specific heat capacity at constant pressure is then calculated by dividing the obtained bulk heat capacity by the bulk mass. The YBCO thermal conductivity is calculated from the obtained thermal resistance considering an equivalent bulk section and length toward the main direction of heat flux. Full article

Electronic and magnetic properties of Ga₁₄N_16−nGd₂C_n monolayers are investigated by means of the first principle calculation. The generalized gradient approximation (GGA) of the density functional theory with the on-site Coulomb energy U was considered (GGA + U). It is found that the total magnetic moment of a Ga₁₄N₁₆Gd₂ monolayer is 14 ${\mu }_B$ with an antiferromagnetic (AFM) phase. C atom substitutional impurity can effectively change the magnetic state of Ga₁₄N_16−nGd₂C_n monolayers to ferromagnetic phases (FM), and the magnetic moment increases by 1${\mu }_B$/1C. The stable FM phase is due to the p-d coupling orbitals between the C-2p and Gd-5d states. Moreover, Curie temperature (T_C) close to room temperature (T_R, 300 K) is observed in the Ga₁₄N₁₆Gd₂C₂ monolayer, and the highest value can reach 261.46 K. In addition, the strain effect has a significant positive effect on the ${\mathrm{T}}_{\mathrm{C}}$ of the Ga₁₄N_16−nGd₂C_n monolayer, which is much higher than the ${\mathrm{T}}_{\mathrm{R}}$, and the highest value is 525.50 K. This provides an opportunity to further explore the application of two-dimensional magnetic materials in spintronic devices. Full article

The reaction of bis(pentafluorophenyl)mercury with the ligands bis(diphenylphosphano) methane P,P’-dioxide ({Ph₂P(O)}₂CH₂) (1), bis{2-(N,N,N’N’-tetraethyldiaminophosphano) imidazol-1-yl} methane P,P’-dioxide ({2-PO(NEt₂)₂C₃N₂H₂}₂CH₂) (2) and bis (2-diphenylphosphanophenyl) ether P,P’-dioxide ({2-PPh₂(O)C₆H₄}₂O) (3) afforded crystalline σ-donor complexes [{Hg(C₆F₅)₂}₂{Ph₂P(O)}₂CH₂] (1Hg), [Hg(C₆F₅)₂{2-PO(NEt₂)₂C₃N₂H₂}₂CH₂]_n (2Hg) and [Hg(C₆F₅)₂{2-PPh₂(O)C₆H₄}₂O] (3Hg), respectively. The molecular structures of 1Hg, 2Hg and 3Hg show considerable differences. In complex 1Hg, a single bridging bidentate ligand connects two three-coordinate T-shape mercury atoms with a near linear C-Hg-C atom array. Complex 2Hg is a one-dimensional coordination polymer in which adjacent four-coordinate mercury atoms with a linear C-Hg-C atom array are linked by bridging bidentate O,O’- ligands, whilst in complex 3Hg a T-shape three-coordinate mercury atom is ligated by (3) in a monodentate fashion. The Hg-O bond lengths of complexes 1Hg, 2Hg and 3Hg differ substantially (range 2.5373(14)-2.966(3) Å) owing to structural and bonding differences. Full article

We present a systematic study of the structural and magnetic properties of a series of powder samples of SrYb${}_{2-x}$Er${}_x$O${}_4$ with different Yb/Er concentrations. Magnetometry and neutron diffraction have been used to study the magnetic ground states of the compound series, while inelastic neutron scattering was used to investigate the crystal field excitations for a chosen concentration. These results show that the crystal structure remains the same for all compositions, while the lattice parameters increase linearly with the Er content. All compounds showed some type of magnetic transition below 1 K, however, both the magnetic structure and nature of the phase transition vary throughout the series. The samples present a non-collinear magnetic structure with the moments lying on the ab plane for low Er content. For high Er content, the magnetic structure is collinear with the moments aligned along the c-axis. A critical concentration is found where there is a bifurcation between zero-field and field-cooled magnetic susceptibility. This irreversible process could be due to the random mixture of single-ion magnetic anisotropies. Full article

X-ray diffraction analysis is essential in studying stacking faults. Most of the techniques used for this purpose are based on theoretical studies. These studies suggest that the observed diffraction patterns are caused by random stacking faults in crystals. In reality, however, the condition of randomness for stacking faults may be violated. The purpose of the study was to develop a technique that can be used to calculate the diffraction effects of the axis of the thin plates of twin, new phases, as well as other variations in defective structures. Materials and methods. This was achieved through modern X-ray diffraction methods using differential equations (transformations and Fourier transforms) and the construction of the Ewald sphere, mathematical analysis, mathematical logic, and mathematical modeling (complex Markov chain). Conclusion. The study made it possible to develop a technique for the calculation of the diffraction effects of the axis of the thin plates of twin, new phases and other variations in defective structures. The technique makes it possible to solve several complex, urgent problems related to the calculation of X-ray diffraction for crystals with face-centered lattices containing different types of stacking faults. At the same time, special attention was paid to the correlations between the relative positions of faults. The calculations showed that the proposed method can help to determine the nature and structure of stacking faults by identifying the partial and vertex dislocations limiting them in twin crystals with a face-centered cubic structure of silicon carbide based on X-ray diffraction analysis. Full article

The impregnation of poorly water-soluble drug onto the surface of a suitable pharmaceutical excipient, used as a hydrophilic carrier, can lead to the preparation of systems with improved dissolution properties due to the separation of drug crystal particles on the carrier surface. For this purpose, a method based on impregnation of hydrophilic matrix by the hydrophobic poorly water-soluble drug Meloxicam (MX) solution in volatile organic solvent was used. After the evaporation of the solvent, the method resulted in coverage of the carrier surface by drug crystals. The influence of the amount and concentration of the impregnating solution on the formed MX crystal size and the dissolution rate was evaluated. Firstly, the impregnation forming crystals on the planar surface was studied and the MX maximum dissolution flux from that surface was determined. The optimum preparation method was further used to produce a volume of impregnated granules. The dissolution performance of the granules was evaluated, and the dissolution kinetics was described by mathematical models. The polymorphic modification of impregnated API and influence of impregnated drug amount on the hydrophilic carrier surface coverage were considered. From the results of this work, it is clear that the impregnated drug amount and the number of impregnations cycles can be optimized to achieve maximum drug release rate. Full article

The critical magnetic field is one of the most interesting properties of superconductors. Thus, this study aimed to investigate the surface and upper critical magnetic fields of superconductors in Fe-based and cuprate superconductors as KFeSe and LaSrCuO superconductors, respectively. The anisotropic two-band Ginzburg–Landau method was used to generate the analytic equation. The analytics were shown for the simplified equation so that a second-order polynomial temperature-dependent equation could be applied and fitted to the experimental results of KFeSe and LaSrCuO superconductors. After that, numerical calculations were applied to find the shape of the Fermi surface, which is an important component within the band structure. It was found that the anisotropy of the Fermi surface for each band structure was affected by the upper critical magnetic field and the surface critical magnetic field to the upper critical magnetic field of the superconductors. The second-order polynomial temperature-dependent model can be applied to other superconductors to predict the surface and upper critical magnetic fields. Full article

The effect of epitaxial strain on the electrical properties of ferroelectric films has been widely investigated. However, this kind of strain is generally attributed to the substrate clamping constraints and is easily relaxed when the thickness of films is over 100 nm. In this work, a vertically epitaxial strain was introduced into lead-free piezoelectric K_0.5Na_0.5NbO₃ films to improve the electrical properties of ferroelectric films. Two-phase, vertically epitaxial composite KNN-ZnO thin films were grown on the (001) STO substrate using a pulsed laser deposition (PLD) method. The highly (001) preferentially oriented KNN phase and (11$\overline{2}$ 0)-oriented ZnO phase were orderly arranged. Two types of morphologies of “square-like” and “stripe-looking” grains were observed in the surface image. An asymmetric “square” out-of-plane phase hysteresis loop and a “butterfly” displacement loop were exhibited in the KNN phase, whereas the ZnO phase showed a closed phase hysteresis loop and a slim displacement-voltage loop. Two different kinds of polarization behaviors for domains were also observed under applied electric fields, in which the domain of the KNN phase is easily switched to the opposite state, whereas the ZnO phase keeps a stable domain state when applying a DC bias of ±50 V. the vertically epitaxial growth of the KNN-ZnO composited films in this work provides a new way to fabricate complex nanoscale materials. Full article

Conventional deep-ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN crystals have extremely low light-emission efficiencies due to the absorption in p-type GaN anode contacts. UV-light-transparent anode structures are considered as one of the solutions to increase a light output power. To this end, the present study focuses on developing a transparent AlGaN homoepitaxial tunnel junction (TJ) as the anode of a deep-UV LED. Deep-UV LEDs composed of n⁺/p⁺-type AlGaN TJs were fabricated under the growth condition that reduced the carrier compensation in the n⁺-type AlGaN layers. The developed deep-UV LED achieved an operating voltage of 10.8 V under a direct current (DC) operation of 63 A cm⁻², which is one of the lowest values among devices composed of AlGaN tunnel homojunctions. In addition, magnesium zinc oxide (MgZnO)/Al reflective electrodes were fabricated to enhance the output power of the AlGaN homoepitaxial TJ LED. The output power was increased to 57.3 mW under a 63 A cm⁻² DC operation, which was 1.7 times higher than that achieved using the conventional Ti/Al electrodes. The combination of the AlGaN-based TJ and MgZnO/Al reflective contact allows further improvement of the light output power. This study confirms that the AlGaN TJ is a promising UV-transmittance structure that can achieve a high light-extraction efficiency. Full article

Gas-atomized Cu-10Sn powders as a potential substitute for sintered bronze layers are usually employed in plain-bearing shells produced by cold spray (CS) processes on steel substrates (AISI 1010). In this study, the effective thickness, i.e., approx. 450 µm, of the bronze overlay required for the bearing shell was successfully and cost-effectively deposited in a short time. A ball-on-disc test setup was used to explore the tribological behavior of cold-sprayed bronze coatings under dry sliding conditions, and the electrochemical corrosion behaviors of sprayed coatings at room temperature were also evaluated by using the potentiodynamic scanning (PDS) technique in acidic (0.01 M Na₂SO₄) and alkaline (3.5% NaCl) environments. The characterization of the sprayed bronze coatings revealed no formation of oxidation or new phases during cold spraying and that the coatings were well-adhered to the substrates, implying good bonding. The wear results demonstrated that, as the load and sliding distance increased, the friction coefficients and wear rates of the sprayed coatings decreased. The PDS results showed that the corrosion resistance of the Cu-10Sn coating layer in an acidic environment is higher than that in an alkaline environment. In addition, the coated layer presented no passivation or pitting onset due to the heavy corrosion reaction in an alkaline solution. Full article

The current work seeks to discover and choose the proper friction stir processing (FSP) settings for aluminum alloy 7075 surface composites enhanced by adding three unique nanoparticles of titanium dioxide (TiO₂), B₄C, and graphene for superior performance. FSP is the only method that produces higher amounts of particle distribution and nanoscale reinforcing. For the sample fabrication, a special relatively high rotational speed of 2000 rpm and feed rate of 45 mm/min were tested with a suitable range of processing parameters (800–2000 rpm, 25–45 mm/min). To measure the micro-hardness and surface roughness of three different surface nano composites, they were studied under various FSP conditions. The findings showed that surface composites produced at high rotational speeds of 1400 rpm and 45 mm/min decreased surface roughness and granule distributions by 39% and 73%, respectively, and increased surface micro-hardness by 54%. According to the microstructure investigations, good bonding was produced between the AA7075 substrate generated at 1200 rpm and the base metal and friction stir processed specimens at 800 and 2000 rpm. The AA7075/B₄C surface composite produced at 1200 rpm rotating speed had a higher micro-hardness than the other two surface composites. Full article

X-ray diffraction theory allows the interpretation of experiments to build a structural model that fits the collected data. As with any experimental science, the observations are subject to uncertainty through the instrument and user limitations. Similarly, the theory can never be perfectly complete; it will have limits, and therefore the resultant model will have uncertainties associated with it. This article discusses the limits of X-ray kinematical and dynamical diffraction theories. These are not the only theories, but are the most widely used. These theories are often extended to accommodate new findings, which can reach the stage at which their fundamental premise is clouded. At that point, the theory requires a rethink. There should be nothing sacrosanct about a theory; it should represent the best usable explanation that will allow a good interpretation of the data. Both kinematical and dynamical theories assume that the X-rays see an average structure, which is not what a photon experiences. The observed diffraction pattern is the average of the diffraction patterns created by all the photons, which is not the same as the diffraction pattern from the average structure. Accounting for this has a profound influence on the interpretation of the data. Full article

Intramolecular electronic communication between electrochemically active groups connected by a bridging moiety can be modified through small changes in the spatial disposition of the redox active moieties and/or by the nature of the central core. In this study, chiral bio-based compounds, namely isomannide and isosorbide, were employed as cheap and easy-to-functionalize chiral scaffolds to bridge two ferrocenyl electroactive moieties. The crystal structures of both bis-ferrocenyl diester complexes were studied and they showed that the chirality of the bridge results in an open or tight helical crystal packing. The electron communication between the two electroactive units in the mixed valent monocations was also investigated using electrochemistry (cyclic voltammetry and differential pulsed voltammetry), and spectroelectrochemistry in the UV-Vis NIR. A computational study through time-dependent DFT was also employed to gain greater insight into the results obtained. Full article

Continual development of nickel-based superalloys for single-crystal turbine applications has pushed their operating temperatures higher and higher, most notably through the addition of rhenium. However, this has left them susceptible to the precipitation of topologically closed packed phases (TCPs), which are widely considered detrimental. Whilst these have long been reported as an end-of-life phenomenon in in-service components, they have more recently been observed during the manufacture of turbine blades. Several rhenium-containing alloys (CMSX-4, CMSX-10K, and CMSX-10N) were cast into single-crystal test bars and studied at different times along their solution heat-treatment process to discern if, when, and where these TCPs precipitated. It was seen that all alloys were susceptible to TCPs at some point along the process, with the higher rhenium-containing alloy CMSX-10N being the most prone. They occurred at the earliest stages of the solution process; this was attributed to aluminium diffusion from the segregated interdendritic regions into the dendrite core, causing the concentration of rhenium into the ɣ-matrixes until sufficient potential was achieved for TCP precipitation. As the samples became more homogeneous, fewer TCPs were observed; however, in the case of CMSX-10N, this took longer than the typical 24-h solution time used in industry, leading to components entering service with TCPs still present. Full article