Ab initio free energy of vacancy formation and mass-action kinetics in vis-activeTiO2

Abstract

Recent reports have identified bulk defects such as oxygen vacancies as key players in visible-light photoactiveTiO2. This would imply greater visible light absorption rates may be possibleprovided effective defect engineering can be achieved. To further thiswe have developed methods to simulate vacancy formation in bulkTiO2 using ab initio techniques. Initial results of these methods show an entropic reduction inthe free energy of vacancy formation of 2.3 eV over a range of 266 K. The use of this result isillustrated by a ‘toy’ mass-action kinetics model which offers insight into vacancyconcentration, rate constants, and enthalpy of reaction.