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

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Abstract
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.