The Effect of Defect Structure on Electrical Conductivity and Thermoelectric Power of La_2-xSr_xCuO_4-δ at High Temperatures

Abstract

The electrical conductivity and Seebeck coefficient of La_2-xSr_xCuO_4-δ with x = 0~0.30 were measured as a function of temperature between room temperature and 100°C and oxygen partial pressure of 1 ~ 1×10^-4.5 atm. From the analysis of the relationship between the electrical conductivity and Seebeck coefficient, it was suggested that a hopping conduction model and a degenerated band conduction one are applicable to electrical conduction of La_2-xSr_xCuO_4-δ when electrical conductivity is less than 30 S cm^-1 and more than 60 S cm^-1, respectively. Combining oxygen nonstoichiometry data with the electrical conductivity and the Seebeck coefficient, it was revealed that the electrical properties of La_2-xSr_xCuO_4-δ at high temperatures are determined only by the Cu mean valence. The concentration of hole carrier is determined by the Cu mean valence and carrier mobility is not dependent of the oxygen nonstoichiometry nor the Sr content. Also revealed was that the Seebeck coefficient of La_2-xSr_xCuO_4-δ is determined only by the Cu mean valence. Although apparent continuous relationship was observed between electrical conductivity, Seebeck coefficient and the Cu mean valence, indicated was that the conduction mechanism changes continuously from hopping conduction to degenerated band conduction at the Cu mean valence of around 2.05 +.