ELECTRICAL-CONDUCTIVITY AND DEFECT STRUCTURE OF CALCIUM-DOPED LANTHANUM CHROMITES

Electrical conductivity of calcium-doped lanthanum chromites, La1-xCaxCrO3-delta, was determined as a function of composition, temperature, and oxygen partial pressure, P(O2), to determine its defect structure and understand its redox behavior. The conductivity was independent of P(O2) and was proportional to the dopant concentration at high P(O2). The activation energy of conductivity was 0.12 to 0.14 eV and the mobility was 0.066 to 0.075 CM2/V/S in the temperature range of 900 to 1050-degrees-C, which was ascribable to small-polaron hopping. Under reducing conditions, the conductivity decreased exponentially with decreasing P(O2) and asymptotically approached a P(O2)1/4 relationship. A simple point-defect model, in which Ca(La)', h., and V(o).. were assumed as predominating defect species, was proposed to elucidate the conductivity variation with P(O2). The oxygen nonstoichiometry calculated based on the defect model was consistent with the reported thermogravimetric data, which verified the soundness of the model.