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 BaTiO3 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 degrees 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.