The nature of iron-oxygen vacancy defect centers in PbTiO3

The Fe 3+ center in ferroelectric PbTiO 3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c -axis. Its microscopic structure has been analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on finestructure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe 3+ for Ti 4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B-site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12 K, exhibiting a c/a -ratio of 1.0721.