Thermal transport in polycrystalline YBa 2Cu 3O 7−δ, Y 2BaCuO 5 and melt-processed YBa 2Cu 3O 7−δ materials

Abstract

Simultaneous thermal conductivity and thermoelectric power measurements are reported for standard polycrystalline YBa 2Cu 3O 7− δ (Y123) samples with oxygen contents covering the range 6.00 to 6.96±0.02, between 20–300 K. The resistivity of each sample over the same temperature range was also determined and the data used to discuss the phonon and electron contributions to the total thermal conductivity in the normal state. The thermal conductivity and resistivity curves for both polycrystalline Y 2BaCuO 5 (Y211) and melt-textured Y123 containing significant amounts of Y211 are used to discuss the insignificant effect of Y211 inclusions in polycrystalline Y123 on the thermal conductivity curves in the vicinity of T c. Longitudinal and transverse thermal Hall measurements on overdoped polycrystalline Y123 in magnetic fields up to 4 T have been used to verify that κ xx el (B=0,T) shows a significant peak at ∼ T c/2, while a two peak phonon contribution is found in the thermal conductivity below T c. The suppression of the longitudinal thermal conductivity for the superconducting state by magnetic fields is also discussed.