© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim EXAFS studies of lattice dynamics and thermal expansion

Accurate temperature-dependent EXAFS measurements can give original information on the correlation of thermal motion in crystals, not only along the bond direction (parallel Mean Square Relative Displacement, MSRD), but also within the perpendicular plane (perpendicular MSRD). This potential is demonstrated by the results obtained for copper and germanium, taken as model systems. Possible applications for investi-gating on the local origin of Negative Thermal Expansion are being supported by measurements on crystals with the cuprite structure. 1 Introduction The acronym EXAFS (Extended X-ray-Absorption Fine-Structure) refers to the oscil-lations observed on the high-energy side of x-ray absorption edges in molecules and condensed systems [1]. EXAFS can be interpreted, within the framework of the time-dependent perturbation theory, as a final state effect due to the interaction of the photo-electron with the neighbouring atoms, the frequencies of oscillations being directly connected to inter-atomic distances. Selectivity of atomic species and insen