Study on vacancy formation in ferroelectric PbTiO3 from ab initio

Formation energies of possible vacancies under different oxygen partial pressures were studied using an ab initio density functional theory and supercell approach. Under oxygen-rich conditions, lead vacancies are the stable ones throughout the band gap, and their ionization level locates at 0.56eV from the top of valence band, which may contribute to p-type conduction. Under oxygen-poor conditions, oxygen vacancies are the stable ones at the top of the valence band. It is a deep donor that may not only dilute the acceptor carriers to weaken the p-type conduction but hardly contribute to n-type conduction.