Ti off-center displacements in Ba1-xSrxTiO3 studied by EXAFS

Local structure of Ba1-xSrxTiO3 with x=0-0.75 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=0.7. 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.