ELECTRICAL CONDUCTIVITIES OF YBA2M3OY (M-FE, CO) SYSTEM

YBa2M3O9-δ (M: Fe, Co) systems with composition similar to the YBa2Cu3O7 superconductor were synthesized. Two types of Y1.2Ba3Fe3Oz (orthorhombic, a = b = 4.06 Å, c = 4.04 Å) and YBa2Fe3O9-δ (tetragonal, a = 3.94 Å, b = 3.92 Å, c = 3.90 Å) with perovskite-type structure were obtained for the iron oxide system, while YBa2Co3O9-δ perovskite (cubic, a = 4.14 Å) was obtained for the cobalt oxide system. The conductivities and the Seebeck coefficients were measured in the temperature range from 650°C to room temperature. The carrier densities and the mobilities were calculated by using a small polaron hopping model. All the samples were p-type semiconductors and showed hopping conduction. The mobility of holes was much larger for YBa2Co3O9-δ than for YBa2Fe3O9-δ, although the unit cell is larger for the former oxide than for the latter. This is explained through the larger overlapping integral of the σ* hopping band formed in YBa2Co3O9-δ than the π* hopping band formed in YBa2Fe3O9-δ. © 1991.