Local structure and dynamics of disordered systems studied by EXAFS

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Abstract
EXAFS spectroscopy has been used to study and compare the local structure in systems of various kinds and degrees of disorder: c-Ge, a-Ge, AgI and AgI-doped superionic glasses. The non-standard cumulant analysis of EXAFS has allowed an accurate characterization of local disorder of both thermal and static origin. Non-Gaussian distributions of interatomic distances and the corresponding anharmonic pair potentials have been reconstructed in a model-independent way from experimental results. Harmonic and anharmonic contributions to thermal disorder have been singled out, leading to refined comparisons with harmonic vibrational models. A strong correlation of vibrational motion of silver and iodine nearest-neighbour ions has been found in both β-and α-AgI. In amorphous systems the cumulant method allows the accurate characterization of local static disorder; as for a-Ge, interatomic distance and coordination number are in very good agreement with neutron diffraction results.

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