Crystal structure, local structure, and defect structure of Pr-doped SrTiO$_3$

TL;DR

This study investigates the structural, local, and defect characteristics of Pr-doped SrTiO3, revealing phase transitions, oxidation states, substitution behavior, and defect types through X-ray techniques and structural analysis.

Contribution

It provides detailed insights into the phase transition, oxidation state, and defect structure of Pr-doped SrTiO3, highlighting the role of Pr ions and defects in the material.

Findings

Structural transition from cubic to tetragonal with increasing Pr content

Pr ions are mainly in the 3+ oxidation state and substitute Sr atoms

Charged Sr vacancies and SrO planar faults are key defects

Abstract

X-ray diffraction studies showed that the structure of (Sr$_{1-x}$Pr$_x$)TiO$_3$ 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$_{1-x}$Pr$_x$)TiO$_3$ 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 Pr$^{3+}$ and Ti$^{4+}$ 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.