EXAFS spectroscopy at synchrotron-radiation beams

Development of the specialized synchrotron radiation (SR) sources of high brightness affords considerable advancement in using absorption-spectroscopy methods for determining the local atomic and electronic structure of absorbing centers in materials science, physics, chemistry, and biology. This review presents the basic theoretical principles of extended x-ray absorption fine structure (EXAFS) spectroscopy, which is one of the mainstream directions of absorption spectroscopy and allows high-accuracy determination of the parameters of the short-range order in multicomponent amorphous and quasicrystalline substances. Methods of analyzing EXAFS spectra with allowance for multiple-scattering effects are described along with experimental procedures implementing EXAFS spectroscopy at SR beams and requirements to the monochromatization of the radiation beam. An energy-dispersive spectrometer, which can provide the time resolution 3-5 ms, is under development at the SR beam at Kurchatov Institute for studying phase transitions and external actions to an object. The EXAFS-spectroscopy results for oxide compounds of tungsten and molybdenum, whose valence varies in dependence of external actions, are presented. One of the structural problems of the physics of fullerenes - temperature dependence of the position of metal atoms-is successfully solved by using EXAFS spectroscopy.