PbTiO3: Dipole moment of a Pb-O vacancy pair

Abstract

The polarization of a nearest-neighbor (nn) Pb-O vacancy pair [(VPb-VO)nn] in PbTiO3 is calculated, using the modern theory of polarization, implemented in the density-functional-theory ultrasoft pseudopotential formalism. The dipole moment per divacancy, μ⃗(VPb-VO)nn, is about 2.28ernn, where rnn is the vector from the VPb site to the VO site. This value is slightly larger than the value of 2ernn for a purely ionic model of PbTiO3. The dipole moment is about twice as large as typical polarizations per cell in Pb-based ferroelectrics, which indicates that VPb compensated by VO can be an important source of local polarization and electric fields in Pb-containing perovskites.