The Fe3+ center in ferroelectric PbTiO3 together with an O vacancy forms a charged defect associate, oriented along the crystallographic c-axis. Its microscopic structure was analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on fine-structure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the Fe ion in the ferroelectric phase was found to be similar to the B site in the para-electric phase. Partial charge compensation was locally provided by a directly coordinated O vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remained tetragonal down to 12K, exhibiting a c/a ratio of 1.0721.

Iron-Oxygen Vacancy Defect Centers in PbTiO3 - Newman Superposition Model Analysis and Density Functional Calculations. H.Meštrić, R.A.Eichel, T.Kloss, K.P.Dinse, S.Laubach, P.C.Schmidt, K.A.Schönau, M.Knapp, H.Ehrenberg: Physical Review B, 2005, 71[13], 134109 (10pp)