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−δ (LSAM; x≤0.3, y≤0.15 and z≤0.1) was measured using the DC four-probe method as a function of temperature (500–1000°C) and oxygen partial pressure (1–10−22 atm). Among LSAMs, (La0.9Sr0.1)AlO3−δ showed the highest ionic conductivity, σi=1.3×10−2 S cm−1 at 900°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, σi, but also the mobility, μv, of [V⋅⋅O]. These properties exhibit a maximum at around [V⋅⋅O]=0.05. With the increase in [V⋅⋅O], the activation energy, Ea, 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, μ0v, and Ea on [V⋅⋅O] was analyzed and their effect on μv and σi 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.