Specific features of phase transitions and the conduction of La2Mo2O9 oxide-ion conducting compound doped with vanadium

The X-ray powder analysis, calorimetric studies, and conductivity measurements of a series of ceramic La₂Mo_2−x V _x O _y specimens with different vanadium content are performed with the aim of following the dynamics of phase formation of the low-temperature α, high-temperature β, and metastable β _ms phases. At x ≥ 0.06, the cubic phase becomes stable and the monoclinic phase vanishes; therefore, the main α → β transition is suppressed. According to the data of differential thermal analyses, a weak thermal anomaly is observed in the range 450–470°C at x ≥ 0.06. This anomaly is indicative of the β _ms → β transition due to the conversion of the cubic phase with statically disordered oxygen atoms into the cubic phase with dynamic disorder. The conductivity of the high-temperature β phase obeys the Vogel-Tammann-Fulcher law.