COEXISTENCE OF ELECTRONS AND HOLES IN BABI0.25PB0.75O3-DELTA DETECTED BY THERMOELECTRIC-POWER MEASUREMENTS

Seebeck coefficients of BaBi0.25Pb0.75O3- (0.000.08) were measured as a function of temperature up to 1100 K in various O2 partial pressures. The Seebeck coefficient of BaBi0.25Pb0.75O3.00 below 300 K was negative by a few V/K and showed linear temperature dependence, indicating a metallic or semimetallic nature of the carrier electrons. Above 300 K, the Seebeck coefficient (=0.00) increased, becoming positive around 400 K. Curve fitting with an assumption of the coexistence of electrons that show delocalized character and holes that have a localized nature was carried out to determine the relationship between the Seebeck coefficients and the temperature of the sample. The temperature dependence of not only the Seebeck coefficient but also the electrical conductivity of the sample could be well explained by the assumption described above. From the comparison with electronic-band calculations, it is deduced that electrons with high mobility and holes with low mobility are the product of delocalized bands composed of Pb(Bi) 6s and O 2p antibonding orbitals and localized bands composed of O 2p isolated orbitals, respectively. The Seebeck coefficients of the samples with values of 0.0250.08 were also slightly negative at low temperatures and had values of 20 V/K at around 1100 K. Finally, it could also be deduced that electrons and holes existed simultaneously in samples with an oxygen deficiency. © 1995 The American Physical Society.