Superior Perovskite Oxide‐Ion Conductor; Strontium‐ and Magnesium‐Doped LaGaO3: I, Phase Relationships and Electrical Properties

The single-phase, cubic-perovskite region of the LaO1.5-SrO-Gao1.5-MgO phase diagram was determined from room-temperature and high-temperature X-ray diffraction. Two impurity phases were identified, LaSrGaO4 and aSrGa3O7. The conductivity of the oxygen-deficient perovskite phase was shown to be essentially a purely oxide-ion conductivity sigmao over a wide range of oxygen partial pressures 10-22 lessthan equal to PO2 lessthan equal to 1 atm. The highest values of sigmao = 0.17 and 0.08 S/cm were found for La0.8Sr0.2Ga0.83Mg0.17O0.2815 at 800° and 700°C, respectively; they remain stable over a week-long test. The Arrhenius plot of sigmao is curved, dividing into a high-temperature region T > T* similar/congruent 600°C and a low-temperature region T < T*. Above T* all the oxygen vacancies appear to be mobile; below T* they progressively condense into clusters of ordered vacancies.

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