Oxygen transport during formation and decomposition of AgNbO₃ and AgTaO₃

A thermogravimetric method was used to analyze intermediate processes involved in the formation and decomposition of AgNbO₃and AgTaO₃perovskites. Critical parameters that control the kinetics of the formation are associated with oxygen transport. The Nb₂O₅crystal structure has a capacity to trap molecular oxygen, which evolves during the decomposition of Ag₂O that is present in a starting mixture. The formation of the perovskite phase involves a simultaneous reaction of three species: O₂, Ag, and Nb₂O₅/Ta₂O₅. As the trapped molecular oxygen is in the immediate vicinity of the reaction site, the kinetics of the reaction is significantly accelerated. An absence of the molecular oxygen in the solid-state phase cannot be compensated for with an increase in a partial pressure of oxygen in the gas phase, that is, application of oxygen atmosphere.