ELECTRICAL-CONDUCTIVITY, DEFECT EQUILIBRIUM AND OXYGEN VACANCY DIFFUSION-COEFFICIENT OF LA1-XCAXALO3-DELTA SINGLE-CRYSTALS

In order to make clear the ionic and electronic conductivities of the perovskite-type La1-xCaxAlO3-delta, single-crystalline samples with x = 0.0027-0.008 were prepared by a floating zone technique. The conductivity and the oxygen nonstoichiometry were measured by a dc four probe method and by a high temperature gravimetry, respectively, both as a function of oxygen partial pressure, P(O2), between 1 and 10(-20) atm and temperatures up to 1100-degrees-C. It was found that the nonstoichiometric change in the oxygen content with P(O2) and temperature was smaller than the experimental errors of DELTAsigma = +/- 0.001. The results were analyzed by a simple defect model assuming Ca(La)' and V(o) as predominant defects and electron holes as minor defects. The conductivity due to electron holes, sigma(h), and due to oxygen vacancy, sigma(i), at temperatures between 700 and 1000-degrees-C are found to be expressed by the equations: sigma(h) = (35 +/- 9)x1/2P(O2)1/4 exp {-(0.56 +/- 0.01) (eV)/kT} S cm-1 and sigma(i) = (2.0 +/-0.8) x 10(5) [x/T) exp {-(0.74 +/- 0.05) (eV)/kT) S cm-1. The oxygen vacancy diffusion coefficient, D(V), was calculated as D(V) = (2.9 +/- 1.2) x 10(-3) exp {-(0.74 +/- 0.05) (eV)/kT) cm2 s-1.