OXYGEN-DOPING DEPENDENCE OF THERMOELECTRIC POWER AND THERMAL CONDUCTIVITY MEASUREMENTS IN EuBa₂Cu₃O_7-δ

Abstract

The temperature variation of thermoelectric power, S(T), and thermal conductivity, &(T), in EuBa2Cu307_ ( 5 polycrystalline samples with various degrees of oxygenation is reported. The temperature dependence in the range of highly oxygenated to deoxygenated samples displays a gradual transformation from metallic-like to semiconductorlike features in the normal state. For 8 values near zero, the critical temperature, indicated by S(T), shows a lowering which is attributed to a possible raising in electron carriers due to oxygen overdoping. Above T c , thermal conductivity is found to decrease with increase in temperature, pointing towards a contribution to thermal resistivity from three-phonon Umklapp processes. Below T c , thermal conductivity increases rapidly before reaching a maximum, attributed this effect to electron-phonon enhancement combined with a temperature dependent defect scattering limitation in the lifetime of the phonons. A nonmonotonic doping dependence on k(T) is indicated in data, suggesting sensitivity to both oxygen content and oxygen order. The experimental set up is described and results discussed.