Influence of nonstoichiometry on ferroelectric phase transition in BaTiO₃

The ferroelectric phase transition behavior in equilibrated nonstoichiometric BaTi O3 powder samples was characterized by a differential scanning calorimeter. The transition temperature (TC) and enthalpy of transition (Δ H TC) between the paraelectric and ferroelectric phases were varied systematically with defect concentrations through the BaTi ratio, temperature, and oxygen partial pressure [p (O2)]. It was observed that the different defects such as titanium, barium, and oxygen vacancies all contribute to the changes of TC and Δ H TC. The TC decreased with increasing concentration of Ti O2 partial Schottky defects and BaO partial Schottky defects. The annealing temperature increased the TC due to a complex mechanism with the increase of full Schottky defect reactions. In terms of p (O2), TC is constant in the ionic compensation region, and increases with the nonstoichiometry in the electronically compensated p (O2) region.