Advanced Materials Research Vols. 26-28

Abstract: The effect of hydrostatic pressure mechanically applied to hydride on the equilibrium hydrogen gas pressure and temperature have been examined theoretically. From free energy calculations where elastic energy is taken into account, equilibrium gas pressure and temperature increases and decreases with increasing applied compressive stress, respectively. In the case of magnesium hydride, equilibrium temperature decreases to 63 °C at the hydrogen gas pressure being 1 atom when volume expansion at hydriding is perfectly suppressed by an external compressive stress. The temperature is remarkably lower than that obtained by alloying various elements.

Abstract: The temperature dependence of single-crystal elastic constants of L10-ordered single-crystals of FePd . A complete set of elastic constants has been determined with the resonance ultrasound spectroscopy technique. The compounds clearly show a tetragonal elastic anisotropy, c11 < c33 and c44 < c66. The temperature dependencies of the anisotropies are not simply explained by the variation of axial ratio (c/a) of the crystal.

Abstract: Electrochemical properties and microstructure evolution during lithiation and delithiation of Ni3Sn2 single crystals with the hexagonal B82-type related ordered structure have been studied as a function of the crystal orientation by charge/discharge tests, powder X-ray diffraction and transmission electron microscopy. Charge and discharge capacities are strongly dependent on the crystal orientation. When the surface of the thin plate anode is perpendicular to the basal plane of the parent B82 unit cell, the capacities are approximately twice as high as those for the sample whose surface is parallel to the basal plane, which is considered to be related to the difference in the diffusion behavior of lithium with respect to the crystal orientation.

Abstract: Manganese-alloyed Ru2Si3-based alloys with various alloy compositions have been prepared and the phase relationships of these alloys have been investigated as a function of the Mn concentration using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A series of Ru1-xMnxSiy chimney-ladder phases is confirmed to be formed over a wide compositional range (x ≥0.12). These chimney-ladder phases are considered to be formed to stabilize the HT-Ru2Si3 chimney-ladder phase through the substitution of Ru with Mn. The compositions of the chimney-ladder phases are, however, significantly deviated from the idealized composition satisfying the valence electron concentration rule: VEC=14.

Abstract: The present paper reports the results of microcreep tests and microstructure of alloy 617 foils of 100μm thick specimens at 800 and 900 oC in air. Before each test, the specimens were annealed in vacuum at 950 oC for 17 hrs. The dynamic recrystallizations were observed during creep test. The voids and cracks were observed along grain boundaries. The maximum elongation of grains was found at the lowest applied stress along the loading direction. The average grain size decreases from 20 μm to 2 μm as applied stress increases from 48 to 120 MPa at 800 oC and from 50 μm to 5 μm as the applied stress increases from 35 to 60MPa at 900 oC. The steady state creep rates were increased as applied stress increased in all the specimens.

Abstract: Textured SrBi2Nb2O9 (SBN) ceramics were fabricated by templated grain growth (TGG) method. The plated-like SBN particles with shape anisotropy prepared by molten salt method were used as the templates. The SBN powders prepared by conventional solid (CS) reaction were used as matrix powders. It was found that the textured SBN ceramics can be obtained by TGG method. The grain orientation (Lotgering factor, f) increased with the increase of sintering temperature and content of the templates. The textured SBN ceramics with f=0.86 could then be obtained after sintering at 1300 °C for 3 h with 20wt.% templates. The relative density keeps rising with increasing temperature until it reaches a peak value 91.22% at the sintering temperature 1300°C, after which it decreases.

Abstract: BaBi4-xLaxTi4O15 (BBLT) ceramics were prepared by conventional solid phase sintering ceramics processing technology. The crystal structure and the microstructure were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD analyses show that La3+ ions doping did not change the crystal structure of BBT ceramics. The sintering temperature increased from 1120°C to 1150°C with increasing Lanthanum content from 0 to 0.5, but it widened the sintering temperature range from 20°C to 50°C and refined the grain size of the BBT ceramic. Additionally, polarization treatment was performed and finally piezoelectric property was measured. As a result, the piezoelectric constant d33 of the 0.1at.% doped BBLT ceramics reached its highest value about 22pc/N at polarizing electric field of 8kV/mm and polarizing temperature of 120°C for 30min.

Abstract: Bismuth titanate was prepared from the sol-gel method. Bismuth nitrate and titanium isopropoxide were used as the starting precursors with the mole ratio of Bi:Ti as 4:3. Solutions were mixed in acetic acid medium and heat at 80 oC for 2h. Sols were obtained after adjusting the final of pH of solution to 2. Gels were formed after drying at 100 oC for 24h. The milled powders were calcined at 500-800 oC for 2h. The phase formation was investigated by X-ray diffractometry (XRD). Single phase with orthorhombic structure of bismuth titanate was obtained after calcination at 700 oC for 2h. The morphology and chemical composition were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The average particle size was 0.50- 1.5 μm with the irregular shape. The elemental composition of bismuth, titanium and oxygen showed the characteristic X-ray energy values.

Abstract: TiB2-TiC ceramic matrix composites were fabricated by in situ synthesis under hot isostatic pressing (HIP) with 3TiH2-B4C and 11TiH2-3B4C being the raw materials, respectively. The XRD analysis indicates that the samples synthesized from 3TiH2-B4C have TiB2 and TiC phases, while those from 11TiH2-3B4C have not only TiB2 and TiCx phases, but also Ti3B4 phase. TiB2-TiCx ceramic matrix composites obtained from 11TiH2-3B4C have better mechanical properties than those from 3TiH2-B4C. The microstructures of the composites are investigated with SEM and TEM. TiB2 grains are platelet grains; Ti3B4 grains have two different morphologies. Ti3B4 phases are formed through two different paths: fine grain Ti3B4 is formed through TiB+B=Ti3B4 at low temperature; large plate-like grain Ti3B4 is formed through TiB2+TiB=Ti3B4 at high temperature.

Abstract: A relaxor ferroelectric material, Pb(Mg1/3Nb2/3)O3 (PMN) powder with a pyrochlore-free phase, was prepared by using a one-step calcinations method. The pyrochlore phase was prevented by coating Mg(OH)2 on Nb2O5 particles. Pure-perovskite PMN powder was synthesized by a single calcination of the coating powder mixed with appropriate amounts of PbO at 900 oC for 2 h. The pyrochlore-free perovskite PMN powders were sintered to 96.9% density at 1100 oC. The sintered PMN ceramics exhibited a dielectric constant maximum of ~11 700 at room temperature at a frequency of 1 kHz.