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 tempe rature (500-1000 degrees C) and oxygen partial pressure (1-10(-22) atm). Am ong LSAMs, (La0.9Sr0.1)AlO3-delta showed the highest ionic conductivity, si gma(i) = 1.3 X 10(-2) S cm(-1) at 900 degrees C. A simultaneous substitutio n 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 effec t. 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 mo bility, 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 ion ic conduction dropped from 1.8 to ca. 1.0 eV at [V-O] = 0.05 and became alm ost constant at [V-O] > 0.05. The dependency of the pre-exponential term, m u(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 t o be a complicated correlation. (C) 2000 Elsevier Science B.V. All rights r eserved.