Kazuo Obara

Variation of electrical properties on growth sectors of ZnO single crystals

We have grown almost dislocation-free ZnO crystals by the hydrothermal method. The variation of electrical properties on growth sectors of these crystals was studied by means of I-V and 1/C 2 -V measurement. Gold contacts were made at the polar faces on each growth sector. In the (0001) faces [O surface] of all the sectors, clear rectifying action was observed. In the (0001) faces [Zn surface] of all sectors, weak rectifying action or nearly ohmic characteristics were observed. These results indicate that the O surfaces tend to induce intrinsic defects like O vacancies and the rectifying characteristics become strong, while Zn surfaces tend to form a metallic face so that the Au contacts become ohmic. The variation of I-V and 1/C 2 -V characteristics on the growth sectors showed that the contacts of m growth sector have better characteristics than those of other sectors.

Solid solution range of boron, microhardness and oxidation resistance of the perovskite type RERh3Bx (RE=Gd, Y, Sc) compounds

Abstract Polycrystalline samples of RERh 3 B x (RE=Gd, Y, Sc), which consists of a reactive RE and high melting point Rh and B elements, are successfully synthesized by the arc melting method. RERh 3 B x compounds have the perovskite type cubic structure (space group Pm 3 m ). Perovskite type phases of GdRh 3 B x and YRh 3 B x exist in the range of ∼0.444≤ x ≤1.000. On the other hand, phase of ScRh 3 B x exists in the range of 0≤ x ≤1.000 (0 to 20 mol% B). ScRh 3 , in the case of x =0, has AuCu 3 type structure; its space group is also Pm 3 m . The lattice parameter a in RERh 3 B x depends on x and the value of a increases with increasing boron content x . The value of Vickers microhardness of the RERh 3 B x at room temperature ranges from 6 to 10 GPa. According to thermo-gravimetric and differential thermal analysis for RERh 3 B x (RE=Gd, Y) heating up to 1200°C in air, a mixed phase of REBO 3 and Rh is identified as an oxidized product. In the case of ScRh 3 B, the oxidized product consists of Rh, Sc 2 O 3 and ScBO 3 .

Dynamic recrystallization of Nb3Al produced from alloy powder

Abstract The deformation behaviour of Nb3Al compressed at above 1300 K was studied using off-stoichiometric, single-phase Nb3Al produced by consolidation of prealloyed and ball-milled powders. It was found that Nb3Al was able to be deformed plastically above 1400 K and the stress-strain curves showed deformation softening after a peak stress. Transmission electron microscopic observations revealed that this deformation softening was caused by dynamic recrystallization. The amount of deformation softening decreases and steady state deformation occurs at an early stage of compression, as the compression temperature increases.

Boron-carbon atomic ratio dependence on the hardness and oxidation resistance of solid solutions of perovskite-type borocarbide YRh3BxC1-x (0 ≤ x ≤ 1)

Solid solutions of the quaternary borocarbide system YRh3BxC1-x have been synthesized and studied from the viewpoints of their microhardness and oxidation resistance. Perovskite-type YRh3B and YRh3C form a continuous solid solution in the range of 0?x?1 with a cubic structure (space group: Pm3m, Z=1). The microhardness of YRh3BxC1-x increases with increasing boron content. The oxidation onset temperature also increases with boron content. Thus, it is indicated that the chemical stability of solid-solution YRh3BxC1-x is strongly dependent on the boron content.

Dissociated dislocations in deformed Nb3Al produced from alloy powder

Abstract Near-stoichiometric Nb3Al containing a small amount of niobium solid solution (3·7 vol%) and alumina (2·5 vol.%), which was produced from Nb-25 at.% Al alloy powders by hot isostatic pressing, was compression tested above 1300 K. The nature of dislocations induced by the plastic deformation was studied using transmission electron microscopy. The dislocations are dissociated into two partial dislocations which bound a stacking fault, These partial dislocations and the stacking faults belong to {100}. The Burgers vector of the partial dislocation and the displacement vector of the stacking fault are both determined to be (a/2)⟨001⟩.

High-Quality Crystalline Silicon Layer Grown by Liquid Phase Epitaxy Method at Low Growth Temperature

We investigated the effect of growth temperature on crystal quality of crystalline silicon layers grown by liquid phase epitaxy (LPE) with gold-bismuth binary alloy solvent. The electrical and structural properties were examined by means of minority-carrier lifetime measurement and micro-Raman scattering spectroscopy. Both electrical and structural qualities improve with decreasing growth temperature. In the present study, the lifetime of the silicon layer grown at the lowest temperature was higher than that of monocrystalline silicon substrate though the solvent includes gold which is a well-known strong recombination site. On the other hand, the structural quality of layers is inferior to that of the substrate even at the lowest growth temperature. Thus, the temperature dependence of lifetime was concluded to be mainly due to the reduction of the solubility of gold impurity in the layer rather than the improvement of structural quality.

Search for Perovskite-Type New Boride in the Sc–Ni–B System

The search for a perovskite-type new boride in the Sc–Ni–B system has been carried out by the arc-melting synthetic method. As a result, the chemical formula of the compound ScNi3B0.5 was obtained for the first time. This compound has the cubic perovskite-type structure (space group: Pm3m) with the lattice parameter a=0.37760(7) nm. ScNi3B0.5 exhibits metallic behavior down to 4.2 K. The magnetic susceptibility of ScNi3B0.5 shows Pauli paramagnetism. No superconductivity appears down to the lowest temperature as determined by electric and magnetic measurements. The micro-Vickers hardness and oxidation resistivity in air are also reported for ScNi3B0.5.

High-Temperature Solution Growth and Characterization of Chromium Disilicide

Single crystals of CrSi2 were obtained in the form of hexagonal prisms by a high-temperature solution growth method using molten tin as a solvent. Their maximum dimensions were approximately 0.3 mm in diameter and 2.5 mm in length. The crystals had hexagonal symmetry with space group P6222 and their lattice parameters were a=0.425(2) nm and c=0.6375(1) nm. The crystals were semiconducting. The value of the micro-Vickers hardness for the {1100} face with hexagonal symmetry was 11.2±0.4 GPa. The weight gain of the crystals heated to 1473 K in air was negligible.