Factors limiting equilibrium in fabricating a simple ferroelectric oxide: BaTiO₃

This paper demonstrates a number of features that can contribute to BaTiO₃ being perturbed from an equilibrium condition. The BaTiO ₃ synthesis study was conducted with a modified citrate process, but the kinetic aspects limiting the equilibrium state are believed to be general to any processing route. The equilibrium conditions can be determined through a detailed analysis of the paraelectric-ferroelectric phase transition data measured by differential scanning calorimeter. Broadened and multiple latent heat peaks are found indicating a distribution of slightly different ferroelectric transition temperatures for nonequilibrated BaTiO₃ materials. A number of factors have been found that limit the equilibrium conditions, and these include time at formation conditions of temperature and oxygen partial pressure, a second phase BaCO₃, and the rapid nucleation of a BaTi₂O₅ phase on quenching to room temperature from temperatures in and around 1250°C. All of these nonequilibrium factors that occurs at high temperature lead to the ferroelectric phase transition having multiple phase transitions, owing to regions of the BaTiO₃ having different partial Schottky concentrations.