Thermal conductivity of partially substituted YBa2Cu3O7-δ

Partially substituted YBa2Cu3O7-δ (Y123) samples are produced by replacing part of the Y with appropriate rare-earth elements and/or part of the Ba with Sr. Partial substitution has little effect on the normal-state resistivity or superconducting transition temperature, but should reduce the phonon part of the thermal conductivity, λp. Ambient temperature measurements on several polycrystalline samples show a thermal conductivity, λ, reduction relative to Y123. The effect persists to lower temperatures and data for Y123 and Y0.5Yb0.5Ba2Cu3O7-δ show that the λ peak at Tc/2 is also affected. copyright 1999 The American Physical Society