Comprehensive Linkage of Defect and Phase Equilibria through Ferroelectric Transition Behavior in BaTiO3‐Based Dielectrics: Part 1. Defect Energies Under Ambient Air Conditions

Abstract

Defect and phase equilibria have been investigated via the ferroelectric phase transition behavior of pure and equilibrated nonstoichiometric BaTiO3 powder samples. Through fabricating the BaTiO3 materials under highly controlled conditions to preserve the equilibrium conditions with respect to Ba/Ti ratio, annealing temperature (T), and oxygen partial pressure (PO2), systematic variations in the phase transition temperature can be noted with respect to Ba/Ti ratio and T. From the data extracted, we can then determine solubility limits. Equilibrating the defect reactions at the solubility limits provides a direct approach to identify and calculate the defect energetics. The phase transition temperature decreased with increasing concentration of the TiO2 partial‐Schottky defects (BaTi1−δO3−2δ) and the BaO partial‐Schottky defects (Ba1−δTiO3−δ), and showed discontinuous changes in the two‐phase region. The formation enthalpy and entropy for the partial‐Schottky defect reactions was evaluated to be 2.32±0.1 eV and 10.15±0.7 kB for the BaO partial‐Schottky defect, and 2.89±0.1 eV and 8.0±1.5 kB for the TiO2 partial‐Schottky defects equilibrated under air annealing conditions.