High-pressure X-ray absorption spectroscopy

The main effect in the application of pressure on the materials is to reduc e the interatomic distances. The modifications in the nature, type and inte nsity in the atomic interactions between the atoms that constitute the samp le may eventually drive to new structures when the pressure is high enough. Many techniques are used to study the matter at high pressure: Raman, infr ared, Brillouin spectroscopies, optical absorption, among others. To get in formation fi om these techniques is necessary to know the state equation V( P) of the material, and the structure (symmetry and atomic positions). The structural characterization techniques as the X-ray diffraction or the neut ron diffraction can be used to get the information, but when the materials are not crystalline the coordination and the interatomic distances are diff icult to determine with these techniques. The X-ray adsorption spectroscopy (XAS) is a sonda of local order around a predefined chemical specimen in t he material. The material can be complex and it does not matter its physica l state: gas, solid or liquid. This technique gives information about the i nteratomic distances between the neighbor shells of the atom, the number in to these shells, and also of the static or dynamic disorder. around the ato m. The I-III-VI2 compound are an example of the XAS precision. These compou nds show a structural change as a function of the pressure: from the tetrac oordinated tetragonal structure <I(4)over bar>2d to the hexacoordinated cub ic structure F3m3. In this work we describe the diamond-anvil cell to gener ate the pressure and the XAS experimental mount. Finally, the possibilities that the XAS offer are shown with some I-II-VI compounds.