Crystal structure, local structure, and defect structure of Pr-doped SrTiO3

X-ray diffraction studies showed that the structure of (Sr_1-xPr_x)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 (Sr_1-xPr_x)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.