Kohji Nobugai

The preparation of NaCl-type Ti1−xAlxN solid solution

Ti1−xAlxN solid solutions (0 ≤ x < 0.6) with NaCl-type structures were synthesized by a rf-sputtering method. The lattice constant of the solid solutions linearly decreases with increasing Al content. For samples withx greater than 0.5, a remarkable lattice distortion was observed.

Association Reaction in Forsterite Under Shock Compression

Transmission electron microscopic observation of forsterite (Mg2SiO4) shocked to peak pressures of 78 to 92 gigapascals revealed that forsterite breaks down to an assemblage of MgO plus MgSiO3 glass. This strongly supports the interpretation that the high-pressure phase of forsterite under shock compression is due to the assemblage of MgSiO3 perovskite plus MgO.

Formation mechanism of pigeonite lamellae in skaergaard augite

Fine textures of exsolution lamellae and interface boundaries between augite and pigeonite in augite crystals from Skaergaard ferrogabbro 4430 have been studied by high resolution electron microscopy and X-ray methods. Thick pigeonite lamellae have higher densities of (100) stacking faults than thin lamellae. The displacement vector of the faults has been determined as 5/6c from the measured density of faults and the relative rotation of the augite and pigeonite lattices. The augite and pigeonite lattices are apparently coherent, and no growth ledges were observed at the interfaces. The stacking faults are often combined with the antiphase boundary of pigeonite resulting in a total displacement vector of 1/2(a+b)+5/6c. The observation of thick and thin pigeonite lamellae indicated that the thickening of (001) pigeonite lamellae was controlled by coherency strains accumulated at the interfaces between augite and pigeonite.

A study of subsolidus relations of the Skaergaard pyroxenes by analytical electron microscopy

Within augite and pigeonite grains of the Skaergaard ferrogabbro 4430, the Ca-poor phases contain only three mole percent of CaSiO3, and the Mg-Fe partition coefficients between the Ca-poor and Ca-rich phases are extremely small with 0.46 for augite and 0.51 for pigeonite grains. These values indicate existence of diffusion within each grain (intragranular diffusion) at considerably low temperatures.The compositions are slightly but definitely different between the Ca-rich phases in augite and pigeonite grains as well as between the Ca-poor phases in augite and pigeonite grains. This indicates that the diffusion among the grains (inter-granular diffusion) has not taken place under the subsolidus condition of the Skaergaard intrusion.

Localized relaxation in stabilized zirconia

Abstract Stabilized zirconia is well known for long-range transport of oxygen ions which is caused by diffusion relaxation of oxygen vacancies. We used torsional vibrations to measure the temperature dependence of internal friction in yttria-stabilized zirconia (YSZ) doped with 9.5 mol % Y2O3 and calcia-stabilized zirconia (CSZ) doped with 12 mol % CaO. In the temperature range 300– 700 K , the internal friction peak exhibits anisotropy, different in YSZ from CSZ, which we attribute to localized relaxation of oxygen vacancies. The results imply that some oxygen vacancies are bound within the local structure, a greater number in CSZ than in YSZ, and suggest that the defect symmetry of local structure depends on the type of dopant ion.

Internal Friction Due to Localized Relaxation around Y-ions in Single Crystal Yttria-Stabilized Zirconia

The internal friction in single crystal yttria-stabilized zirconia (YSZ) doped with 9.5 mol% Y2O3 was measured for longitudinal sound waves in the frequency range from 10 Hz to 800 Hz using a vibrating reed technique. In the temperature range from 300 K to 700 K, observations of internal friction reveal two closely overlapping absorption peaks, confirming the existence of two relaxation modes in YSZ. One of the peaks is due to diffusion relaxation, which is known to be responsible for long-range transport of O-ions. The second peak shows clearly the existence of localized relaxation, which is attributed to bound oxygen vacancies within the local structure which is formed around an Y-ion due to symmetry breaking. The absorption peak caused by the localized relaxation exhibits anisotropy resulting from the asymmetric local structure, and the strength of this peak changes with temperature reflecting the number of bound oxygen vacancies.

Phase transition in B1-type Mo1−xNbxN sputtered films under ammonia annealing

Abstract B1-type solid solution Mo 1− x Nb x N sputtered films were annealed at 500–900°C for 5–100 hr under flowing ammonia, in order to investigate the stability of B1 structure and phase transition in the solid solution as a function of annealing temperature and chemical composition x . The B1 phase of the MoN films ( x = 0) transferred to a hexagonal phase above 600°C. In the Mo-rich solid solution films with x ≦ 0.23, the B1 phase was converted to the γ-Mo 2 N-type phase between 600°C and 800°C, and the transition temperature increased with increases in x . A hexagonal solid solution with WC-structure was formed in the films with x ≦ 0.38 at 900°C. No phase transition occurred until 900°C in the Nb-rich solid solution films with x ≧ 0.59 . The result indicates that the stability of B1 structure in the solid solution was increased by the addition of NbN.

ULTRASONIC ATTENUATION DUE TO LOCALIZED RELAXATION IN CUBIC YTTRIA-STABILIZED ZIRCONIA

Longitudinal ultrasonic attenuation in yttria-stabilized zirconia [ZrO2(Y)] was measured at frequencies of 10 MHz and 120 MHz and at temperatures between 300 and 600 K. The temperature variation was strongly anisotropic, the maximum effect being observed in the direction. At 10 MHz a relaxation peak was observed from which an activation energy of 0.7 ±0.07 eV could be estimated. A similar figure was obtained from dielectric constant measurements, but the ionic conductivity yielded a higher value of 0.92 ±0.1 eV. Our conclusion is that there are two separate hopping processes for oxygen ions, one between Zr-related sites which can percolate the crystal and hence produce conduction, and another between Y-related sites which are localized.

Crystallizations of Amorphous Y-Ba-Cu-O Film Prepared by RF-Sputtering

Amorphous YBa 2 Cu 3 Oy itself and YBa 2 Cu 3 Oy containing F or excess amount CuO films were prepared by rf-sputtering. Film texture such as preferred orientation and superconductivity were investigated on these films crystallized in oxygen flow at various temperatures. Substrate effects were also studied on MgO (100) and SrTiO 3 (100) and (110) in relation to applied rf-power on sputter deposition. The addition of foreign elements were effective to lowering the crystallization temperature on MgO substrate. The preferred orientations of YBCO on SrTiO 3 changed with the deposition conditions of amorphous film

Preparation and superconductivity of WC structure type Mo1−xNbxN thin films

WC structure type Mo1−xNbxN (x≦0.38) solid-solution thin films have been prepared by annealing the corresponding as-sputtered films (NaCl-type solid solution) in flowing ammonia gas at 900°C for 5–24 hr. The films exhibited a metallic temperature dependence of electrical resistivity and superconductivity. As x changed from 0 to 0.23, the residual resistivity ratio, r=ϱ(300K)ϱ(20K), and the superconducting transition temperature, TC, of the films varied from 4.0 to 1.5 and from 14.9 to 11.0 K, respectively. The tendency of variation of TC with Nb content in the films is similar to that calculated for the corresponding NaCl-type solid solutions.