DEFECT STRUCTURE OF Y1-YCAYMNO3 AND LA1-YCAYMNO3 .1. ELECTRICAL-PROPERTIES

Electrical conductivity and the Seebeck coefficient of compositions in the system Y1-yCayMnO3 and La1-yCayMnO3 were studied to determine the mechanism of electrical transport and defect structure. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 ≤ y ≤ 0.80. The Seebeck coefficient data did not support the assumption that Mn is present in Cadoped Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which includes the thermally excited disproportion of Mn3+ and Mn4+ pairs. The Seebeck data were explained with this model by assuming that divalent Mn cations were site blockers in the conduction process. © 1993 Academic Press, Inc.