XAFS studies of the local structure and charge state of the Pr impurity in SrTiO₃

Abstract

Solid solutions of (Sr_{1 − x} Pr _x )TiO₃ have been studied using X-ray methods. It has been shown that, with an increase in the praseodymium concentration, the temperature of the structural phase transition to the phase with space group I4/mcm increases and, at x ≥ 0.15, the structure at 300 K is tetragonal. X-ray absorption fine structure (XAFS) spectroscopy studies have revealed that Pr ions are predominantly in the charge state 3+ and occupy the Sr sites. No indications of the off-centering of Pr atoms at the Sr sites have been revealed. The local environment of Pr atoms is characterized by a strong relaxation of the oxygen atoms, the value of which corresponds to the difference between the ionic radii of Pr³⁺ and Sr²⁺. It has been found that, in the second shell, there occurs a significant repulsion of the Pr³⁺ and Ti⁴⁺ ions, which is responsible for the weak dependence of the lattice parameter in the solid solution on the praseodymium concentration.