Factors Limiting Equilibrium in Fabricating a Simple Ferroelectric Oxide: BaTiO ₃

This paper demonstrates a number of features that can contribute to BaTiO 3 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 BaTiO 3 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 BaCO 3 , and the rapid nucleation of a BaTi 2 O 5 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 BaTiO 3 having different partial Schottky concentrations.