HIGH-TEMPERATURE ELECTRICAL-PROPERTIES OF THE PEROVSKITE-TYPE OXIDE LA1-XSRXMNO3-D

In order to elucidate the conduction mechanism of the perovskite-type oxide La1-xSrxMnO3-d (0 less than or equal to x less than or equal to 0.4), the electrical conductivity, sigma, and Seebeck coefficient, Q, were measured as a function of temperature, T, up to 1100 degrees C in 1 atm O-2 gas and as a function of the oxygen partial pressure, P(O-2), at 800-1100 degrees C. At T > similar to 200 degrees C, sigma T increased with T, indicating that thermally activated type conduction may predominate irrespective of x. The Q values were generally positive, indicating that p-type conduction was predominant. The quantity of Q was relatively small in comparison with other perovskite-type oxides, implying that these materials are metallic, irrespective of whether the conduction is thermally activated or itinerant. The relationship between sigma and Q for x less than or equal to 0.2 can be interpreted in terms of a multi-level hopping conduction model by calculating the distribution of electrons in high-spin and low-spin levels of Mn3+ and Mn4+ using statistical dynamics. For x = 0.3 and 0.4, a calculation based on this model revealed that the energy difference between high-spin and low-spin states was smaller than k(B) T, and the calculated hopping mobility gave either a negative activation energy or a negative pre-exponential factor, suggesting that the hopping model is not applicable and that the electrons are itinerant. The electronic nature of the oxides therefore changes from localized to itinerant between x = 0.2 and x = 0.3.