XAFS studies of local structure in perovskites and high Tcsuperconductors

In many material systems the local structure deviates from the average structure not only because of lattice dynamics. Many experiments indicate that the local symmetry is lower than the average macroscopic symmetry on time scales which are longer than ordinary lattice vibration times. These local distorsions can be either frozen or dynamic with typical time constants which can span many orders of magnitude and may be strongly temperature dependent. Information on the local structure and its temperature dependence can be often of considerable value because they are system specific and can provide useful insight into physical phenomena taking place in these systems.