Reducible and non-reducible defect clusters in tin-doped indium oxide

Density functional theory calculations are used to estimate the energy of interstitial oxygen (O_i) released from tin-doped indium oxide (ITO). The currently accepted explanation of defect clusters' irreducibility is based on different arrangements of doping atoms around O_i. In the present contribution we demonstrate that this concept has only a limited domain of applicability and explains the relative stability of different defect clusters with the same and fixed Sn:O_i ratio. To describe practically the important case of ITO treatment under strong reduction conditions another limiting case of varying Sn:O_i ratio is considered. It is found that in this particular case local coordination of doping atoms around O_i plays only a minor role. The relative stability of the oxidized defect clusters has caused a noticeable change in the electronic part of the defect formation energy, i.e. the chemical potential of the conduction electrons determines the equilibrium concentration of the interstitial oxygen atoms.