Influence of nonstoichiometry on ferroelectric phase transition in BaTiO3

The ferroelectric phase transition behavior in equilibrated nonstoichiometric BaTiO3 powder samples was characterized by a differential scanning calorimeter. The transition temperature (T-C) and enthalpy of transition (Delta H-TC) between the paraelectric and ferroelectric phases were varied systematically with defect concentrations through the Ba/Ti ratio, temperature, and oxygen partial pressure [p(O-2)]. It was observed that the different defects such as titanium, barium, and oxygen vacancies all contribute to the changes of T-C and Delta H-TC. The T-C decreased with increasing concentration of TiO2 partial Schottky defects and BaO partial Schottky defects. The annealing temperature increased the T-C due to a complex mechanism with the increase of full Schottky defect reactions. In terms of p(O-2), T-C is constant in the ionic compensation region, and increases with the nonstoichiometry in the electronically compensated p(O-2) region. (c) 2007 American Institute of Physics.