Ti off-center displacements inBa1−xSrxTiO3studied by EXAFS

Abstract

Local structure of ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{TiO}}_3$ with $x=0\mathrm{}–0.75$ has been studied using x-ray-absorption fine-structure spectra, measured at the Ba K edge at room temperature. The dependence of the mean-square relative displacements and the third cumulant of Ba-O and Ba-Ti distribution functions on the Sr concentration have been analyzed. The results show that Ba off-center displacement vanishes abruptly at $x=0.3,$ which is the boundary point between tetragonal and cubic phases, whereas Ti off-center displacement decreases gradually with Sr concentration and approaches zero at about $x=\mathrm{0.7.}\mathrm{}$ The change of macroscopic symmetry does not cause any significant change of Ti displacement. The results indicate that Ti atoms are disordered in a wide range of Sr concentration.