Free energy dependence of pure phase iron doped bismuth titanate from first principles calculations.

A density functional theory study of Fe substitutions in Bi2Ti2O7 photocatalyst (Fe-BTO) is presented. It models an experiment where H2 production of Fe-BTO peaked for samples loaded with 1% Fe concentration then decreased for samples with heavier loadings. The total energy calculations were used to determine defect formation energies and the chemical potential landscape that suggests the observed formation of Fe2O3 (in samples at 2% Fe concentration) was detrimental to H2 production. Doping configurations as a function of oxygen chemical potential are discussed, and the chemical potential ranges that avoid formation of the Fe2O3 phase in Fe-BTO are predicted.