THERMAL-CONDUCTIVITY OF SUPERCONDUCTING LA2-XSRXCUO4 AND SEMICONDUCTING GD2-XSRXCUO4 AT HIGH-TEMPERATURE

The thermal conductivity of superconducting La2-xSrxCuO4 (x =0.10, 0.1 5 and 0.20) and of semiconducting Gd2-xSrxCuO4 (x = 0.00, 0.10, 0.15 a nd 0.20) has been measured between 300-1000 K in air. In the case of t he La-oxides it is highly anomalous, showing a linear increase with te mperature which cannot be explained either by a two-level system (TLS) or a hopping fracton model, and seems to be determined mainly by ther mally-generated electronic defects in addition to configurational diso rder. In contrast, the conductivity of the Gd-oxides follows a T-1 rel ation, and also decreases with increasing strontium content. The condu ctivity dependence on temperature and strontium concentration is found to arise from enhanced phonon scattering due to mass difference and l attice strain; calculations using a simple theoretical model show that the latter effect is more pronounced than the former.