Hideyuki Fujisawa

Olivine-spinel transition in the system Mg2SiO4-Fe2SiO4 at 800°C

Abstract Olivine-spinel solid solution equilibria in the system Mg 2 SiO 4 -Fe 2 SiO 4 have been studied over the pressure range 45 to 92 kb at 800°C. The solid solubility of Mg 2 SiO 4 in the Mg 2 SiO 4 -Fe 2 SiO 4 spinel solid solution increases to 27 mole % over this pressure range. The corresponding olivine solvus was determined up to 63 mole % of Mg 2 SiO 4 over the same pressure interval.

Elastic wave velocities of forsterite and its β‐spinel form and chemical boundary hypothesis for the 410‐km discontinuity

A method for measuring elastic wave velocities at pressures up to 15 GPa has been developed. Velocities of forsterite and β-spinel were measured using a piston-cylinder apparatus with a pulse-echo-overlap method for pressures up to 4 GPa and using a split-sphere apparatus with a pulse-transmission technique for higher pressures. To validate the results, volume compression, incompressibility, and rigidity were estimated from measured travel times, and comparison was made between the present estimates and data from X ray, Brillouin, and acoustic measurements. The V p and K values for β-spinet are 3 and 8% higher than previous measurements at 10 GPa, respectively. Velocity jumps in V p and V s due to olivine to β-spinel transition were about 1.34 and 0.80 km s -1 , respectively, very different from seismological observations of velocity jumps at the 410-km discontinuity, which were concentrated around 0.45 km s -1 for the P wave and 0.22 km s -1 for the S wave. Velocity jumps in mantle peridotite were calculated using the experimental results, and comparison was made between these estimates and seismological observations at the 410-km discontinuity. The evidence does not support the phase-change hypothesis, and a chemical boundary was proposed as the origin of the 410-km discontinuity. An eclogitic mineral assemblage might be an alternative for the composition of the transition layer.

Lattice parameter evidence of intermediate valence of Pr atoms in laves phases PrxR1−xFe2 (R = Sm, Tb and Y)

Abstract The pseudo-binary Laves phases Pr x R 1− x Fe 2 (R = Ce, Sm, Tb and Y) were prepared using high pressure technique for the first time. Lattice parameters for Pr x Sm 1− x Fe 2 , Pr 2 Tb 1− x Fe 2 and Pr x Yin1− x Fe 2 show negative deviation from Vegards linear relationship. We have discussed the results in terms of intermediate valence of Pr atoms under lattice pressure.

Search for superconductivity in PrRh4B4 and CeRh4B4 synthesized under high pressure

Abstract We have successfully prepared PrRh 4 B 4 and CeRh 4 B 4 with the CeCo 4 B 4 -type structure under high pressure and at high temperature. PrRh 4 B 4 shows a superconducting transition at 4.6 K and the upper critical field H c 2 at 0 K is found to be 6.8 kG. The temperature dependence of the upper critical field indicates no re-entrant superconductivity down to 1. 4 K. CeRh 4 B 4 does not show superconductivity nor any magnetic ordering down to 1.4 K. The lattice parameters of CeRh 4 B 4 suggest the valence of 3.4 for cerium.

Magnetostriction in laves phase compounds RE1−xPrxFe2 (RE = Ce, Sm and Y) and their easy axes of magnetization

The pseudo-binary Laves phase compounds RE1−xPrxFe2 (RE = Ce, Sm and Y) were successfully synthesized applying the high pressure technique. We have measured magnetostriction in the compounds at 77 and 293 K and discuss the results in relation with the magnetic anisotropy determined by Mossbauer spectroscopy.

Synthesis of RERh4B4 (RE=Ce, Pr and Nd) at high pressures and temperatures

Abstract We have tested the applicability of high pressure technique to the synthesis of NdRh 4 B 4 and CeRh 4 B 4 with special reference to the effect of the size of the rare earth atom on the phase stability. Applying a pressure of 20 kbar to NdRh 4 B 4.8 at 1400°C, we obtain a composite of the superconducting NdRh 4 B 4 phase, the ferromagnetic NdRh 3 B 2 phase and RhB phase. We succeed in preparing PrRh 4 B 4 by applying 33 kbar at 1500°C. Its superconducting transition temperature is about 4 K. We have failed to synthesize CeRh 4 B 4 under conditions of 25 kbar and 1350°C.