Extending the family of oxygen ion conductors isostructural with La_2Mo_2O_9

摘要

X-ray diffraction characterization of materials prepared by solid-state reactions in the ternary systems La_2Mo_2O_9-Nd2W_2O_9-"Nd_2Mo_2O_9~" and La_2Mo_2O_9-Pr_2W_2O_9-Pr_2Mo_2O_9 has shown that, in these systems, compounds isostructural with the oxygen ion conductor La_2Mo_2O_9 exist in wide single-phase regions. Partial tungsten substitution for molybdenum may yield stable Ln_2Mo_(2-2x)W_(2x)O_9 compounds with the La_2Mo_2O_9 structure, where Ln is a rare-earth element different from lanthanum and praseodymium, e.g., neodymium. Tungsten also stabilizes Pr_2Mo_2O_9, which otherwise decomposes above 700 °C. A series of continuous solid solution was found in the La_2Mo_2O_9-Pr_2Mo_2O-9 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.