The iron(III) center in ferroelectric PbTiO3 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 Fe3+ for Ti4+ 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.
@article{arxiv.cond-mat/0504728,
title = {The nature of iron-oxygen vacancy defect centers in PbTiO3},
author = {H. Mestric and R. -A. Eichel and T. Kloss and K. -P. Dinse and So. Laubach and St. Laubach and P. C. Schmidt and K. A. Schoenau and M. Knapp and H. Ehrenberg},
journal= {arXiv preprint arXiv:cond-mat/0504728},
year = {2007}
}