Oxygen nonstoichiometry of undoped BaTiO3-delta

Oxygen nonstoichiometry (delta) of "undoped", polycrystalline BaTiO3-delta (but with two different nominal purity) has been measured as a function of oxygen partial pressure in the range of 10(-15) less than or equal to P-O2/ atm less than or equal to 0.1 at elevated temperatures (1073 less than or e qual to T/K less than or equal to 1273) by a solid-state coulometric titrat ion technique. Each isotherm varies sine-hyperbolically against log(P-O2) w ith an inflexion point therein (corresponding to the electronic stoichiomet ric composition or delta = 0). The nonstoichiometry variation is attributed to oxygen vacancies compensated mostly by background and/or intrinsic acce ptors in the higher P-O2 region and by electrons in the lower P-O2 region. The purity effect on nonstoichiometry is discussed. The intrinsic electroni c excitation equilibrium constant is evaluated and compared exhaustively wi th the reported. The relative partial molar enthalpy and entropy of compone nt oxygen are also evaluated as functions of the nonstoichiometry. (C) 2001 Elsevier Science B.V. All rights reserved.