Superior Perovskite Oxide‐Ion Conductor; Strontium‐ and Magnesium‐Doped LaGaO ₃ : I, Phase Relationships and Electrical Properties

The single‐phase, cubic‐perovskite region of the LaO 1.5 ‐SrO‐Gao 1.5 ‐MgO phase diagram was determined from room‐temperature and high‐temperature X‐ray diffraction. Two impurity phases were identified, LaSrGaO 4 and aSrGa 3 O 7 . The conductivity of the oxygen‐deficient perovskite phase was shown to be essentially a purely oxide‐ion conductivity sigma o over a wide range of oxygen partial pressures 10 ‐22 lessthan equal to P O 2 lessthan equal to 1 atm. The highest values of sigma o = 0.17 and 0.08 S/cm were found for La 0.8 Sr 0.2 Ga 0.83 Mg 0.17 O 0.2815 at 800° and 700°C, respectively; they remain stable over a week‐long test. The Arrhenius plot of sigma o 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.