XAFS Study of Local Structure Change in Perovskite Titanates

The Ti K-edge EXAFS for PbTiO3 measured in the temperature range including the critical temperature (763K) due to the phase transition from tetragonal to cubic phase is discussed from the local point of view. Three kinds of atomic pairs, shorterTi-O(1),mediumTi-O(2) and longerTi-O(3)were analyzed independently. The interatomic distance of Ti-O(3) changes at Tc discontinuously and shows a “displacive” type transition. On the other hand, EXAFS shows that the lattice distortion remains even in cubic phase, which indicates “order-disorder” type transition. The peak intensity at the pre-edge region in XANES, which indicates the distortion of Ti atoms along the c-axis of the oxygen octahedron, corresponds to the distortion obtained from EXAFS analysis.