Extending the family of oxygen ion conductors isostructural with La2Mo2O9

X-ray diffraction characterization of materials prepared by solid-state reactions in the ternary systems La2Mo2O9–Nd2W2O9–“Nd2Mo2O9” and La2Mo2O9–Pr2W2O9–Pr2Mo2O9 has shown that, in these systems, compounds isostructural with the oxygen ion conductor La2Mo2O9 exist in wide single-phase regions. Partial tungsten substitution for molybdenum may yield stable Ln2Mo2−2xW2xO9 compounds with the La2Mo2O9 structure, where Ln is a rare-earth element different from lanthanum and praseodymium, e.g., neodymium. Tungsten also stabilizes Pr2Mo2O9, which otherwise decomposes above 700 °C. A series of continuous solid solution was found in the La2Mo2O9–Pr2Mo2O9 system. Polymorphism of compounds existing in the above ternary systems was studied by differential scanning calorimetry. The conductivity of most of the compounds studied approaches that of lanthanum molybdate.