THERMAL-CONDUCTIVITY AND ELECTRICAL-RESISTIVITY OF THE Y-SUBSTITUTED AND ER-SUBSTITUTED 1 2/3 SUPERCONDUCTING COMPOUNDS IN THE VICINITY OF THE TRANSITION-TEMPERATURE/

The thermal conductivity and electrical resistivity of ErBa2Cu3O7-delt a and YBa2Cu3O7-delta sintered compounds have been measured to investi gate the electron-phonon interaction in the vicinity of T(c) in these materials. The thermal conductivity was measured using the transient-p lane-source technique. With the electrical-resistivity data and Wiedem an-Franz law, the magnitude of the free-carrier component of the therm al conductivity has been estimated to less than 15% of the measured th ermal conductivity. The results in the normal state are interpreted in terms of two models. The first model is the ordinary electron-phonon transport theory applied to high-T(c) superconductors, and the second model is the Bardeen-Rickayzen-Tewordt (BRT) theory of the lattice hea t conduction in high-T(c) superconductors. Both models suggest that th e electron-phonon coupling varies from moderately weak to strong coupl ing depending on characteristic parameters of the considered material such as oxygen content, porosity, T(c) value, DELTAT(c), etc., all of which are directly related to the purity of the investigated samples. Furthermore, using this transient technique a dramatic increase of the thermal conductivity is observed below T(c) and the experimental resu lts are in reasonable agreement with the prediction of the generalized BRT theory, adapting a weak coupling with scaled-BCS-gap formalism fo r the moderately-weak-coupling sample and a strong coupling s-wave-pai ring formalism for the strong-coupling sample.