First-principles study of neutral defects in Fe-doped cubic barium titanate

The DFT formalism within the GGA+U approximation has been used to investigate the effect of iron doping in the cubic phase of barium titanate. It has been found that aliovalent incorporation of iron at titanium sites, with charge compensation by the creation of oxygen vacancies, is the mode with the lowest energy, although self-compensation may exhibit similar energies under some circumstances. The incorporation of iron also results in a distortion of the charge distribution around the oxygen vacancy and in the appearance of several deep impurity levels within the energy gap. The same effects were evident for all the incorporation mechanisms. The impurity levels agree well with the theory for charge traps in semiconductors in all cases. Finally, the results are compared with the scarce experimental data available.