Synthesis and phase transitions of oxide-ion conducting compound La2Mo2O9 doped with alkaline metals

The specific features of synthesis, polymorthism, and electric conductivity of oxide-ion conducting compounds La_{2 − x} Me _x Mo₂O_{9 − y} , where Me = Na, K, Rb, or Cs, have been studied. Ceramic samples were obtained by solid-state synthesis in the temperature range of 960–1100°C. The regions where solid solutions exist have been found to depend on the temperature of the sample firing. According to the calorimetric and electrophysical data, the phase transition from the monoclinic phase (α) to the cubic phase (β) in samples doped with potassium and rubidium disappears at x = 0.02 and 0.04, respectively. In these cases the only transition from the cubic β _ms phase to the high-temperature cubic β phase is observed near 450°C. Doping with sodium and cesium does not suppress the α → β phase transition.