An accurate theoretical study on intrinsic defect energetics in rutile TiO2

An accurate theoretical study on the intrinsic point defects in rutile TiO2 was carried out by first-principles calculations using plane-wave pseudopotential method. The structural parameters of defect-free bulk rutile TiO2 were calculated, which are close to experimental data. And the effects of point defects on the geometry structures were analyzed. To get accurate value of formation energy and charge transfer levels, several technical details must be considered, such as the position of E-VBM originating from supercell size and electrostatic interactions between the charged defects, and band-gap error etc. The formation energies of the point defects in various charge states were given as a function of Fermi level for the two limiting values of extreme O-rich conditions and extreme Ti-rich conditions. Under extreme Ti-rich conditions, Ti4+ interstitial and V-O(2+) have very low formation energy, and wound thus exist in significant quantities, namely, producing the intrinsic n-type TiO2. The stability of these point defects is traced back to the multivalence of titanium. Under extreme reducing condition, Frenkel defect comprised of Ti-i(4+) and V-Ti(4-) would be formed in TiO2.