Low temperature phase transition phenomena in Ba- and Pb-substituted La2Mo2O9 oxide ion conductors

Abstract The low-temperature phase transition phenomena in Ba- and Pb-substituted La2Mo2O9s have been investigated by means of thermal analysis, TEM observation and conductivity measurements. The low-temperature stable β′ phase appears even in Ba- and Pb-substituted La2Mo2O9 by annealing the supercooled β-phase at around 400 °C as the case of Bi-substituted system. After annealing the samples at different temperatures and time, the observed endothermic heat at β′-β transition was fitted to Avrami's equation to discuss the kinetics of the transformation. From the activation energies of the obtained rate constant, it was found that β′-phase formation proceeds easier in Ba- and Pb-substituted La2Mo2O9 rather than in Bi-substituted system. HR-TEM observation suggested the superstructure of β′-phase, and the thermal hysteresis in conductivity also supported the formation of β′-phase as detected by thermal analysis.