Oxygen nonstoichiometry (delta) of TiO2-delta-revisited

Abstract

Oxygen nonstoichiometry (delta) of "undoped" polycrystalline TiO2-delta has been measured as a function of oxygen partial pressure in the widest ever examined range of 10(-18) less than or equal to P-O2/atm less than or equal to 10(-1) at elevated temperatures (1073 less than or equal to T/K less than or equal to 1473) by thermogravimetry and coulometric titrometry combined and compared with all the reported values. Isothermal variation of nonstoichiometry against P-O2 is explained with a defect model involving quadruply ionized titanium interstitials, electrons, holes, and unidentified acceptors which may be background impurity acceptors or cation vacancies. The equilibrium constants for intrinsic electronic excitation reaction and redox reaction are determined from the nonstoichiometry measured and compared exhaustively with all the reported values. The relative partial molar enthalpy and entropy of oxygen are evaluated as functions of nonstoichiometry and the inner workings of their variations discussed. (C) 2004 Elsevier Inc. All rights reserved.