The effect of oxygen vacancy on the oxide ion mobility in LaAlO3-based oxides

The electrical property of (La1-xSrx)(1-z)(Al1-yMgy)O3-delta (LSAM; x less than or equal to 0.3, y less than or equal to 0.15 and z less than or equal to 0.1) was measured using the DC four-probe method as a function of temperature (500-1000 degrees C) and oxygen partial pressure (1-10(-22) atm). Among LSAMs, (La0.9Sr0.1)AlO3-delta showed the highest ionic conductivity, sigma(i) = 1.3 X 10(-2) S cm(-1) at 900 degrees C. A simultaneous substitution at A and B sites or A site deficiency is expected to create larger oxygen vacancy and higher ionic conductivity. However, it showed a negative effect. The effect of the vacancy increase did not effect monotonously the ionic conductivity. It was found that the concentration of oxygen vacancy, [V-O], influences not only the oxide ion conductivity, sigma(i), but also the mobility, mu(v), of [V-O]. These properties exhibit a maximum at around [V-O] = 0.05. With the increase in [V-O], the activation energy, E-a, of the ionic conduction dropped from 1.8 to ca. 1.0 eV at [V-O] = 0.05 and became almost constant at [V-O] > 0.05. The dependency of the pre-exponential term, mu(v)(o), and E-a on [V-O] was analyzed and their effect on mu(v) and sigma(i) was discussed with respect to crystal structure and defect association. It was estimated that the crystal structure mainly governs these properties. The effect of defect association could not be ignored but is considered to be a complicated correlation. (C) 2000 Elsevier Science B.V. All rights reserved.