Papers by Keyword: Single Crystal

Abstract: Seed crystal stabilization during the initial stage of 200-mm 4H-SiC crystal growth is critical for achieving high-quality wafers with large diameters. This study investigated the effects of heating ramp rates (0 - 6 °C/min) and SiC source powder porosity through both simulation and experimental approaches. Low ramp rates resulted in surface degradation of the seed crystal, whereas high ramp rates induced significant thermal stress, leading to cracking. Optimal ramp rates of 3 - 5 °C/min significantly minimized damage caused by seed crystal loss. Furthermore, high-porosity source powder facilitated adequate gas transport channels, thereby enhancing seed crystal stability. Crystals grown under these optimized conditions demonstrated improved edge morphology, absence of polycrystalline inclusions, and low dislocation densities, with threading screw dislocations (TSD) below 500 cm^-2 and basal plane dislocations (BPD) below 1,000 cm^-2. These results demonstrate that precise control of thermal parameters and source powder porosity offers an effective strategy for stable seed attachment and reproducible growth of high-quality, large-diameter SiC single crystals.

Abstract: To prepare bulk single-crystal REBCO superconductors by the new single-direction growth method (SDMG: Single-Direction Melt-Growth), it is necessary to produce a large-area seed of high quality, for example, based on EuBCO. Since the samples prepared by the SDMG method copy the structure of the seed, for the production of large-area seeds it is necessary to optimize the time-temperature regime in order to grow seeds with a suitable structure and composition and minimize structural defects (limiting the amount of subgrains and others). A higher growth rate was used in comparison with the standard growth rates used to produce EuBCO seeds of larger dimensions. The increased growth rate in the crystal growth window reduces the outflow of the melt from the sample, and thus it is possible to achieve a single-crystal sample in the entire volume of the precursor. The samples were produced at different growth rates: 1; 2; 3 and 5 °C/h. The microstructure of the samples was studied by polarized light microscopy and scanning electron microscopy. The size and distribution of Eu211 particles in the sample volume and the subgrain structure were studied on the fabricated samples.

Abstract: DL-valinium maleate [DLVM] compound was grown as single crystals at room temperature by gradual evaporation from an aqueous solution. The classical nucleation theory was examined to maximize the growth conditions for producing high-quality crystals, Nucleation kinetics studies reveal that the crystal has been grown at room temperature 313 K for which predicted critical supersaturation is 6.19. The grown compound DLVM crystallized in a triclinic system with a centrosymmetric space group P1, according to single crystal and powder X-ray diffraction experiments. The lattice parameters were calculated as a= 6.17 Å, b= 9.68 Å, c= 10.59 Å, α= 105.75°, β = 105.67º and γ = 104.69° with unit cell volume 548.2 ų. The presence of functional groups in the grown compound has been identified by using Fourier Transform Infrared [FTIR] experiments. NMR studies were used to examine the structural features of DLVM compounds. Since the grown material belongs to the centrosymmetric space group, the material has been found to exhibit third-order NLO property. The Z-scan technique was used to analyse the third-order nonlinear behaviour of the grown crystal. The technique was very useful in evaluating the nonlinear refractive index n₂, absorption co-efficient β, and nonlinear optical susceptibility χ⁽³⁾ of the grown material. Hence, the grown crystal finds useful applications in optoelectronics. The antibacterial activity of the title compound was also studied by using the Agar disc diffusion method against the standard bacteria Klebsiella pneumonia, Staphylococcus aureus and Enterococcus faecalis. The results of the antibacterial activity experiment show that the synthesized DLVM crystal will be a good option for the creation of antibiotic medicines that will combat the tested bacterial strains.

Abstract: Single crystal of [Ni(4-AP)₄(NCS)₂] complex compound has been obtained using solvothermal method at 70 °C for 15 hours (yield = 41%). Crystal structure of [Ni(4-AP)₄(NCS)₂] has a distorted octahedral structure with orthorhombic crystal system, Pccn space group, Z = 4, and a, b, and c values of 17.1091(5) Å, 9.6686 (3) Å, 16.1998 (5) Å. Hirshfeld Surface analysis shows that intermolecular hydrogen bonds in the complex compound comes from N–H∙∙∙∙N and N–H∙∙∙∙S. The intermolecular interactions are dominated by H---H, C---H/H---C, and H---S/S---H by 39.0%, 29.6%, and 24.7%, respectively. The relatively less contributions are N---H/H---N, S---C/C---S, and S---N/N---S at 6.3%, 0.2%, and 0.1%, respectively. The [Ni(4-AP)₄(NCS)₂] complex has antibacterial activity against Escherichia coli and Staphylococcus aureus.

Abstract: Ni-rich layered oxide cathode materials LiNi_xCo_yMn_zO₂ (x>0.6) have been widely used in high specific energy Li-ion batteries. Compared with polycrystalline LiNi_xCo_yMn_zO₂, single crystal Ni-rich cathode materials have attracted much attention for their unique advantages. However, they also suffer from some drawbacks, such rapid capacity decay and intragranular crack during cycling. In order to enhance the structure and electrochemical performance of single crystal LiNi_0.8Co_0.1Mn_0.1O₂ (SC811), different amount of aluminium (1 mol%, 2 mol% and 3 mol%) is utilized to substitute the materials. Physical characterizations of SC811 show the successful synthesis and Al doping of the single-crystal materials as well as lower Li/Ni intermixing after Al doping. Electrochemical tests illustrate that the single-crystal materials doped with 2mol% Al (2Al-SC811) shows superior electrochemical performance, and maintains 83.5 % of the initial discharge capacity after 100 cycles at 1 C in comparison with 68.9 % of the pristine SC811. It is hoped this work should shed light on the development of advanced cathode materials for Li-ion batteries.

Abstract: The novel bicycloamino acid, 1−carboxyl−4−amino−2−aza−3−oxo−[2.2.2] bicyclooctane was synthesized and its physical characteristics have been compared to those predicted using quantum chemical calculations. The crystal structure of novel compound was determined by X-ray diffraction measurements at room temperature. Unit cell is monoclinic, with space group P 2₁/n (14) and a = 5.8587(6) Ǻ, b = 11.2454(16) Ǻ, c = 13.9723(16) Ǻ, β=97.840(6)°, Z = 2. Refinement was performed using all 1598 reflections with R = 0.4085 and wR = 0.6024. Theoretical calculation of full optimization and atomic net charge, and frontier orbital energies of the title compound was carried out at the B3LYP/6−31G(d,p) level. The NMR chemical shielding tensors and vibrational frequencies were calculated with B3LYP/6-311+G(2d, p)− level in which were close values and similar spectrum structures with experimental results and used to interpret the experimental measurements.

Abstract: The microstructural evolution of DD9 single crystal superalloy turbine blade was studied after heat treatment. In comparison to the as-cast microstructures where the sizes of the γ′ precipitates have an obvious difference between the dendritic core and interdendritic regions, the γ′ sizes of the heat-treated microstructures tend to be uniform and more cubic. And in the heat-treated microstructures, the γ′ sizes and the related size dispersion degrees of the dendritic cores are slightly increased, while those of the interdendritic regions are obviously decreased. After all, all the γ′ sizes follow the normal distribution law. With the raise of section thickness, the γ′ sizes tend to increase and the related size dispersion degrees are enhanced during the cooling process after heat treatment, and the γ-γ′ eutectics are dissolved, left little residual eutectics and pores.

Abstract: The single crystals of MSe₂ (M = Nb, Mo, Ta and W) were grown through vapour phase by screw dislocation mechanism. The development of stresses by variation in high temperature of the dual zones involved, resulting into slip lines and vapour inclusion, might possibly lead to generation of favourable screw dislocation sites. The morphology of as grown crystals has been studied by TEM. From this analysis, the general rule that nanoparticles of compounds, crystallizing in layered structures tend to form closed shapes. The formation of closed shapes reduces the number of dangling bonds on the periphery of the layers.

Abstract: The paper presents the results of experimental studies of the electro-optical properties of β-Tl_1-xCu_xInS₂ (0 X 0,015) single crystals. It was found that in measurements of the induced birefringence, the transmission of the polarizer - crystal - analyzer (P-C-A) system is nonzero both for the presence of an external electric E = 0 and in its absence, which is apparently associated with the presence of internal fields arising in crystals during their growth ().

Abstract: By the method of thermal oxidation of n-type CuInSe2 crystals, n - n+ structures with a maximum absolute current photosensitivity of up to 10 mA / W were obtained at low rectification and no-load photovoltage. The used modes of thermal oxidation led to the formation of n-type layers on the surface of the n-CuInSe2 plates, the resistivity of which is 2-2.5 times higher concerning the initial substance. Measurements of the stationary current-voltage characteristics have shown that the structures obtained have a slight rectification K. All the structures obtained exhibit photosensitivity, which dominates when illuminated from the side of the layer in the spectral region of about 1 eV. The optimization of the process can reveal the technological possibilities of a significant improvement in the rectifying properties of isotypic structures based on CuInSe2.