The Ferroelectric Phase Transition in PbTiO₃ from a Local Perspective

XAFS of Pb and Ti in PbTiO3 provides quantitative information on the local structure of this ferroelectric perovskite. It was found that both Pb and Ti remain in off center positions above Tc. The local distortions above Tc are about 50-70% of their values at 15 K. The local distortions above Tc are correlated over at least several unit cells. These results suggest that the off center displacements of the Pb and Ti are caused by local interactions and not just by a force field associated with the order parameter