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.