Hiromitsu Ogasawara

Anomalous lattice distortion in Pr-substituted double-layered Perovskite manganite La1.2Sr1.8Mn2O7 single crystals: II

Thermal expansion and magnetostriction both in the a b -plane and along the c -axis of double-layered perovskite manganite (La 1- z Pr z ) 1.2 Sr 1.8 Mn 2 O 7 ( z =0, 0.2, 0.4 and 0.6) single cryst...

Thermal transport of Pr substituted YBa2Cu4O8 compounds with CuO double chains

Abstract We have studied the influence of Pr substitution on thermoelectric power and thermal conductivity of (Y 1− x Pr x )Ba 2 Cu 4 O 8 ( x =0, 0.7, 0.8, 0.9 and 1.0) compounds with CuO double chains. Low-temperature thermal transport of the Pr substituted YBa 2 Cu 4 O 8 compounds has been discussed on the basis of metallic property along CuO double chains.

Thermal transport of Pr2Ba4Cu7O15−y compound with alternative repetition of a single- and double-chain

Abstract We have studied thermoelectric power ( S ), thermal conductivity and magnetoresistance (MR) of Pr 2 Ba 4 Cu 7 O 15− y (Pr247) compound with the alternative repetition of a single- and double-chain. The value of S in Pr247 showed a metallic behavior at lower temperatures, accompanying the appearance of MR effect as well as Pr124. This finding is discussed on the basis of the metallic conduction along the CuO double chain.

Thermal conductivity and diffusivity of Nd2−xCexCuO4

The thermal conductivity κ(T), thermal diffusivity α(T) and electrical resistivity ϱ(T) of sintered Nd2−xCexCuO4 (0 ⩽ X ⩽ 0.2) were measured for ‘annealed’ materials. ϱ(T) decreased with increasing Ce concentration and only the sample of X = 0.2 showed metallic behavior. The thermal conductivity showed maximum near X = 0.15, at which the superconductivity occurred. Taking account of the phonon-phonon interaction, κ(T) was analyzed based on the Tewordt and Wolkhausen (TW) theory. The phonon scattering by electrons was confirmed to be very small up to X = 0.15 and it became discernible only for X = 0.2.

Thermal conductivity of Pr doped YBa2Cu3Oy and a quasiparticle contribution

The thermal conductivity κ of Pr doped YBa2Cu3Oy (Y1−xPrxBa2Cu3Oy) polycrystals has been studied as a function of temperature from 10 K up to 150 K. A pure YBCO crystal exhibits a clear enhancement in κ belowTc but for highly Pr doped samples (x>0.2) the temperature dependence of κ monotonically decreases with reducing temperature. Furthermore, the value of κ of insulating PBCO (x=1.0) is strongly suppressed compared with that of superconducting YBCO. Such behaviour is not explained by the electron-phonon interaction model proposed by Bardeen, Rickayzen and Tewordt but suggests a picture in which an observed peak belowTc in κ of the pure YBCO sample is ascribed to a quasiparticle contribution.

Thermal expansion, thermal conductivity of MMTG-YBa2Cu3Ox and phonon-phonon interaction

The ab-plane thermal expansion αab of a c-axis oriented YBa2Cu3Ox crystal prepared by MMTG process has been studied from 77 K to room temperature using a differential transformer method. The ab-plane thermal conductivity κab of the same sample has been investigated from 10 to 200 K. The phonon scattering mechanism containing phonon-phonon scattering (Umklapp scattering) is discussed based on a relaxation time approximation of phonon to the measured thermal conductivity. The Gruneisen parameter in the ab-plane estimated from the thermal expansion measurement is comparable with that obtained from the phonon-phonon scattering strength.

A Model Analysis of the Thermal Conductivity of Ag-doped Bi-Sr-Ca-Cu-O Superconducting Oxide

A phenomenological model to analyze the transport phenomena in inhomogeneous materials is proposed and applied to the measured thermal conductivity of Ag-doped Bi–Sr–Ca–Cu–O (Bi2212) superconducting oxide. Based on the model, the effective ratios of the doped Ag amount in the grain boundary to that inside of the grain are determined to be 0.75:1.0 for a Bi2212+15 wt%Ag specimen and 0.85:1.0 for a Bi2212+10 wt%Ag specimen. The model analyses indicate that doped Ag particles preferentially occupy the grain boundaries, contributing to the formation of the linked Ag heat path in the oxides.

Possibility of Ag2O+YBa2Cu3O7−X ceramics for low temperature thermoelectricrefrigeration

Abstract Ag 2 O doped and oxygen deficient YBa 2 Cu 3 O 7−X (0 2 O concentrations up to 40wt.% were studied for the thermoelectric refrigeration use in the temperature range from 10K to 260K. The amount of the oxygen deficiency (X) was controlled by varying the thermal quenching temperature. The Seebeck coefficient S, the electrical resistivity ϱ and the thermal conductivity κ were measured and the systematic dependence of these quantities and the figure of merit (Z) on Ag 2 O doping were observed.