Combined Ab Initio and Interatomic Potentials Based Assessment of the Defect Structure of Mn-Doped SrTiO 3

The energetics of doping SrTiO 3 with Mn is investigated using density functional theory calculations within the GGA + U scheme and lattice statics simulations. Defect formation energies are derived for different Mn charge states and for occupation at both the Sr- and Ti-sites. For the GGA + U calculations, due consideration is given to finite-size effects and the treatment of the chemical potential of atomic oxygen to avoid errors associated with direct DFT calculations of the oxygen dimer. The lattice statics calculations have been completed using a recently developed potential model designed for the investigation of rare-earth and transition metal doping of SrTiO 3 . Intrinsic defects have also been considered in all possible charge states. The GGA + U calculations predict that for the three different thermodynamic environments examined both Mn 2+ and Mn 4+ ions occupy the Ti-site via either oxygen vacancy compensation (Mn 2+ ) or no charge compensation (Mn 4+ ). This is contradictory to the lattice statics calculations which predict Mn 2+ doping at the Sr-site and Mn 4+ at the Ti-site. Experiment suggests that Mn 2+ doping at both the Sr- and Ti-sites is possible.