X-ray diffraction studies showed that the structure of (Sr1−xPrx)TiO3 solid solutions at 300 K changes from the cubic Pm3m to the tetragonal I4/mcm with increasing x. The analysis of XANES and EXAFS spectra of the solid solutions revealed that Pr ions are predominantly in the 3+ oxidation state, they substitute for Sr atoms and are on-center regardless of the preparation conditions. The weak dependence of the lattice parameter in (Sr1−xPrx)TiO3 on the Pr concentration was explained by the competition between the relaxation of the Sr--O bond length, which results from the difference in ionic radii of Sr and Pr ions, and the repulsion of positively charged Pr3+ and Ti4+ ions. It was shown that the most important defects in the crystals are charged Sr vacancies and SrO planar faults; praseodymium does not enter the Sr sites in the planar faults.
@article{arxiv.1203.3066,
title = {Crystal structure, local structure, and defect structure of Pr-doped SrTiO$_3$},
author = {I. A. Sluchinskaya and A. I. Lebedev and A. Erko},
journal= {arXiv preprint arXiv:1203.3066},
year = {2012}
}