Gendo Oomi

Observation of the Persistent Photoconductivity Due to the DX Center in GaAs under Hydrostatic Pressure

Persistent photoconductivity due to the DX center in GaAs under a hydrostatic pressure of about 30 kbar has been observed for the first time. The characteristic temperature-dependent photoconductivity observed in GaAs under pressure is quite similar to that in AlGaAs alloy system. This indicates that the DX center in GaAs under hydrostatic pressure has also a large lattice relaxation owing to the AlGaAs-like conduction band structure.

Effects of hydrostatic pressure on the dielectric properties of hexagonal barium titanate around the 222K structural phase transition

Temperature dependence of the dielectric constant of hexagonal BaTiO3 has been studied at a variety of hydrostatic pressures up to about 10kbar. The phase transition point T0 = 222K decreases with pressure: dT0/dp = -3.4K kbar-1. The hexagonal crystal deforms slightly and it changes to orthorhombic below T0 (a′(ortho.) ∼ a(hex.) ∼ 5.72A, b′(ortho.) ∼ √3a(hex.) and c′(ortho.) ∼ c(hex.) ∼ 13.96A). Temperature dependence of lattice parameters has been examined. No anomaly has been detected in c′ parameter at T0, however thermal expansion coefficient αa′ for a′ axis changes the sign below T0. The difference of the volume thermal expansion coefficient above and below T0(Δβv = 19 × 10-6K-1) and the dT0/dp are used in the Ehrenfest relation; the specific heat anomaly at T0 is estimated as ΔCp = 4.7 J mol-1·K-1.

Effect of crystal field on the thermal expansion coefficients of CeCu6

Abstract Linear thermal expansion coefficients (α) of the dense Kondo substance CeCu 6 have been measured from 6 to 300 K. The magnetic part of α, α m , is estimated by using the α of LaCu 6 . α m of the b axis has a well-defined positive maximum around 30 K but α m of the c axis increases with decreasing temperature below 30 K with a small negative minimum near 30 K. The relation between α m and crystal electric field (CEF) is discussed.

Effect of pressure on the electrical resistivity of the dense Kondo compound Ce(In0.8Sn0.2)3

Abstract Electrical resistivity ϱT of the dense Kondo compound Ce(In0.8Sn0.2)3 has been measured under high pressure up to 23 kbar. The Kondo temperature TK is found to increase with increasing pressure. The result in the present work can be explained qualitatively by assuming a simple relation between JN(0) and the volume V, where J and N(0) are the exchange interaction and the density of states at the Fermi level.

Magnetovolume effect of invar alloys under high pressure

Abstract Pressure effects on the spontaneous volume magnetostrictions, ωs(T), of ternary Invar alloys Fe65(Ni1−xMnx)35 with x = 0.16 and 0.25 are studied by measuring the pressure dependence of the lattice constant in the temperature range from 77 to 420 K. The alloy x = 0.16 is found to show anomalous behavior at high pressure: (i) ωs(T) decreases below 100 K with decreasing temperature, (ii) the bulk modulus in the pressure-induced phase is smaller than that in the paramagnetic state at 77 K. For the alloy x = 0.25, the same behavior as (ii) is also observed below 100 K. From these results, it is suggested that the pressure induced phase of x = 0.16 at 77 K may be a spin glass or a mictomagnetic phase. The present results are compared with the ones for Fe65Ni35 and Fe72Pt28 Invar alloys.