Defect engineering of titanium dioxide: full defect disorder

Abstract

Titanium dioxide (rutile) is known as n-type semiconductor. Recent studies show that prolonged oxidation of pure n-type TiO2 may lead to its conversion into a p-type semiconductor. It has been documented that the conversion is associated with the formation of titanium vacancies. The present work derives the defect disorder model of TiO2, which explains the effect of oxygen activity on the concentration of all point defects, including titanium vacancies, and the related semiconducting properties. The derived defect diagram, plotting the concentration of all ionic and electronic defects in TiO2 within a wide range of oxygen activity [10–15 Pa<p(O2)<105 Pa], allows to predict the effect of oxygen activity on semiconducting properties of rutile within both n- and p-type properties. This diagram may be used in the selection of processing conditions of p-type TiO2 from n-type TiO2. The present work also considers the kinetic aspects related to the imposition of defect equilibria associated with titanium vacancies. The real chemical formula of rutile, representing the semiconducting properties within both n- and p-type regimes, is derived.