Papers by Keyword: Lattice Parameter

Abstract: The paper presents the results of tests of metallic materials at low temperatures. It is shown that with the decreasing of temperature, the mechanical characteristics of materials change significantly: strength limits, yield strength increase, and relative elongation decrease. It is shown that the temperature of the brittle-viscous transition depends on the lattice parameter of the materials. The higher the lattice parameter is, the lower is the temperature of the brittle-viscous transition. It is shown that the lattice parameter can be used to estimate the temperature of the brittle-viscous transition

Abstract: This paper reports the properties of Bi-2223 superconductors that had been doped with Fe₂O₃ at Cu-site of the system. It was prepared in bulk form using high purity oxide powders via solid state reaction technique with intermediate grinding. A series of x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 of Fe were stoichiometrically added to the well balanced of Bi_1.6Pb_0.4Sr₂Ca₂Cu_3-xFe_xO_y in order to trace the effect of Fe doping. Hence, electrical resistivity, X-ray diffraction and Field Emission Scanning Electron Microscopy have been carried out to assess the effects of Fe doping. These measurements indicate that Fe doping decreased the critical temperature and degrade the formation of high T_c phase compared with the undoped sample. The orthorhombicity parameters were increased due to substitution of Cu ³⁺ ion by Fe ²⁺ ion.

Abstract: Theoretical molecular dynamic simulations based on plane-wave and pseudopotential density functional theory (DFT) calculations with CASTEP code were employed to explore the pressure influence on the properties of silicon carbide polytypes. The changes in lattice and electronic structures of 2H-, 4H-, and 6H-SiC polytypes at room temperature were investigated when pressures from 10 GPa to 200 GPa were applied. It’s found that the applied pressures didn’t cause a change in the hexagonal structure of the crystals, however the structural and electronic properties clearly affected by the compression. The dependences of volume reduction (V/V_o) and lattice parameters (a and c) on pressure were obtained successfully. The lattice parameters of the polytypes and c/a ratio showed a same trend under the compression with a clear similarity between 4H and 6H. The total energy-volume and enthalpy-pressure relations were estimated. The calculated energy gaps showed a reduction in the band gap width of 4H and 6H with the pressure increase while 2H band gap increased gradually with pressure. The tendency toward decreasing the density of state (DOS) at the conduction band edge was similar among the polytypes.

Abstract: In the research, the properties of barium titanate - bismuth sodium titanate [(1-x)BaTiO₃-(x)Bi_0.5Na_0.5TiO₃: (1-x)BT-(x)BNT] ceramics prepared by conventional mixed oxide method with various molecular weight of BNT or x between 0.0 and 0.3 were investigated. The optimum condition for calcined powders of x = 0.0 was found at 900 °C for 2 h, and x = 0.1 - 0.3 were found at 850 °C for 2h. The calcined powders were pressed and sintered at 1000 – 1200 °C for 2h. The phase structure was examined by x-ray diffraction (XRD). The microstructure was examined by scanning electron microscopy (SEM). Density of sintered samples was measured by Archimedes method with distilled water as the fluid medium. It was found that, all various x of (1-x)BT-(x)BNT ceramics XRD patterns display the tetragonality increased with increasing sintering temperature. All the peaks shift to higher angles when increasing x value indicating the decrease of lattice parameter “a” and increase of lattice parameter “c”. The average grains size of (1-x)BT-(x)BNT ceramics was increased with increasing sintering temperature. The highest density was 5.53 g/cm³ and was obtained from the sample sintered at 1200 °C.

Abstract: The cerium-substituted yttrium-iron garnet (Ce-YIG) in Ce_xY_3–xFe₅O₁₂ is considered as a promising material for applications in high frequency wireless communication technology. In this work, we reported the structural properties of Ce-YIG. This material was produced via conventional solid state reaction (CSSR) with various molar ratio of cerium (x = 0.0, 0.1, 0.5, 1.0, and 1.5, respectively). A heat treatment was at a temperature of 1420 °C for 6 h after pre-fired at 1100 °C for 6 h. Multiple phases were presented in Ce-YIG ceramics. It was found, at x=1.5, the substitution of Ce into YIG has reached the solid solution limit. It was seen that, the peaks were shifted to the lower angle and proportional to the amount of Ce added. Thus, it can be concluded that, the substitution of Ce into YIG was successfully at x=0.1,0.5, and 1.0 respectively before reaching the solid solution limit at x=1.5.

Abstract: Cu - SiC composite powders were discussed in this paper the microstructure after ball mill, through to the ball mill after Cu-SiC composite powder particle size and lattice constant analysis, confirmed the high-energy ball mill to Cu-SiC micro structure of the binary alloy. The experimental results show that the ball mill after 20 h, Cu particle size has a larger extent reduce after high-energy ball mill and SiC lattice constant increase.

Abstract: The paper presents results of the Rietveld refinement method in X-ray diffraction quantitative phase analysis of calcium mono-aluminate, the mineral. It has been stated that the theoretical calcium mono-aluminate CaO⋅Al₂O₃. is a high-stable phase, mixing energy of which is equal to 16214,10 eV. Ab-initio calculations and Rietveld refinement method were used to identify die structural state of CaO⋅Al₂O₃.

Abstract: By X-ray diffraction and scanning electron microscopy using the method of back-scattered electrons the parameters of the solid solution (the lattice parameter and the mean-square displacement of atoms) and the grain boundary ensembles in the alloy Pd₃Fe with the superstructure L1₂ have been investigated depending on the degree of the long-range atomic order. The relationship between the proportion of the twins Σ3 in the spectrum of special boundaries and the mean-square displacement of atoms was detected.

Abstract: Lead-free piezoelectric ceramics of (1-x)(K_0.5Na_0.5)NbO₃ - xCaZrO₃ (abbreviated as KNN-CZ, x = 0 ~ 0.04) were synthesized by the conventional solid state method. Their phase structures and piezoelectric properties were investigated with x-ray diffraction (XRD), Scanning Electron Microscope (SEM), d₃₃ meter and Impedance Analyzer. KNN-CZ samples exhibit only pure perovskite phases with a small monoclinic distortion. It was observed that the lattice parameter b has a maximum at x = 0.02 but the monoclinic distortion angle β shows a minimum at the same composition. From the dependence of the lattice parameters (a, b, c, β) and cell volume on the content of CZ, it is considered that the intermediate phase transition exists near at x = 0.02. Piezoelectric properties show the maximum value of d33 = 121 pC/N and kp = 0.35 for the sample with x = 0.02, which seems to be due to the co-existence of the two different phases.

Abstract: The room temperature residual stress of 4H-SiC wafers has been investigated using a precise X-ray diffraction method. A large strain was observed for the circumferential direction of wafers, more than ten times larger than those measured along the principal plane direction and the radial direction. Optimizing the lateral temperature distribution in growing crystals leads to reduction of residual stress of wafers with high crystal quality.