Yosuke Fujine

Magnetic, electrical and thermal properties of La0.80Sr0.20(MnyCo1−y)O3

Abstract The thermal conductivity κ, thermoelectric power S, electrical resistivity ρ and magnetization M of La0.80Sr0.20 (MnyCo1−y)O3 has been measured. By Mn substitution for Co, the initial ferromagnetic-metal behavior is promptly suppressed and ρ(T) becomes semiconductive. In the semiconductive composition range, S is remarkably enhanced and κ is reduced. As a result, pretty large values of the thermoelectric figure of merit Z are realized.

Homogenous magnetic field generation by high-Tc oxide superconductors

Recently, there are many reports on high performance high-Tc 123 bulk superconductors and applications of various magnetic field environments realized by such high performance 123 bulk materials. Realization of homogeneous magnetic field for industrial NMR/MRI system is also an interesting subject. Since the current density distribution in a 123 bulk superconductor field cooled (FC) in a magnetic field lower than maximum trapped field is identical to a thin solenoid coil, we tried to realize a homogeneous field generation by a pair of high-Tc bulk material in a Helmholtz arrangement. This paper reports computer simulations and experimental results of high homogeneity magnetic field generation by use of a pair of high-Tc 123 bulk super-conductors in a Helmholtz arrangement.

Thermal Conductivity Anomalies of RECoO3 (RE = La-Nd) Related to Valency and Spin State of Co Ion

The thermal conductivities κ( T ) of Co- and La-site-substituted LaCoO 3 were measured and the origin of the κ( T ) peak was investigated. The sharp κ( T ) peak at approximately 30 K is strongly suppressed by the introduction of a small amount of Jahn–Teller (JT)-active Co 4+ ions because of Co-site substitution by divalent ions such as Ni 2+ and Cu 2+ , similarly to the La-site substitution by Sr 2+ . In contrast, the κ( T ) peak of samples with the Co-site substituted by tetravalent ions such as Sn 4+ and Zr 4+ , which introduce Co 2+ ions, moderately decreased. The temperature at which a small and broad κ( T ) peak in the Pr-containing RECoO 3 [rare-earth (RE) = La 1- y Pr y and Pr 1- z Nd z ] is also observable shifts from 110 K for RE = La 0.5 Pr 0.5 to 180 K for RE = Pr and Pr 0.5 Nd 0.5 , which corresponds to the spin-state transition temperature of Co 3+ ions.

Enhanced thermoelectric properties at x/spl sim/0.1 in La/sub 1-x/Sr/sub x/CoO/sub 3/ and La/sub 1-x/Sr/sub x/(Co/sub 1-y/M/sub y/)O/sub 3/ (M=Cr, Cu)

The thermoelectric properties of the La/sub 1-x/Sr/sub x/CoO/sub 3/ system have been investigated from 10 K to 300 K. The figure of merit Z and power factor P increase with increasing Sr concentration x and show a maximum for x=0.10-0.15, where the ferromagnetic (FM) order starts to appear. The maximum Z value (Z= 150 x 10/sup -6/ K/sup -1/ at 230 K for x=0.10) is larger than those of layered cobaltites. The Z and P values are enhanced by the 5 % Co-site substitution by Cr for the overdoped concentration (x=0.20), but are depressed for the nearly optimum doped one (x=0.15). The results are discussed in conjunction with the carrier density n of this system.

Search for p-type oxide thermoelectrics - cobaltites

The thermal conductivity, thermoelectric power, electrical resistivity and magnetization of the 3D perovskites Ln/sub 1-x/AE/sub X/CoO/sub 3/ (Ln=La,Y and AE=Ca and Ba) and the low dimensional Ca/sub 3/Co/sub 2/O/sub 6/ and Ca/sub 3/Co/sub 4/O/sub 9/ cobaltites were measured in a wide temperature range up to 1000 K. As a novelty we demonstrate the prospective high power factor of the. Y/sub 0.9/Ca/sub 0.1/CoO/sub 3/ at high temperatures and, simultaneously, that in the La/sub 1-X/AE/sub X/CoO/sub 3/ system the maximum Z and P values are observed at the phase boundary between the FM and SG state at X/spl sim/0.1 and exceed that reported for layered cobaltite ceramics.