Structure of and phase transformations in bulk amorphous (GaSb)1-x(Ge2)x

Amorphous materials are not new to scientists and mankind -- man has been using glass and glassy materials for centuries. However the scientific study of amorphous materials did not start until the beginning of this century. The technique solid state amorphization is even newer. The method brings an excellent opportunity to study the structure of amorphous materials due to the relative simplicity of preparation of a large amount of the material. This allows use of some characterisation methods which cannot be easily applied to thin films (e. g. direct compressibility measurements, neutron scattering). It also makes easier the studies of three dimensional percolation processes, and phase transformations in general, and significant contributes to the understanding of physics of disordered solids. The importance of structural studies can hardly be overestimated. Structure determines the major properties of materials: electrical, elastical, thermo-dynamical etc. However, until now the subject of structural studies of amorphous materials is an area of wide debate and comprehensive picture still has to be built. In this work I have presented the results of a structural study of bulk amorphous solid solutions (GaSb)1-x(Ge2)x prepared by solid state amorphization under high pressures. The most powerful method for structural investigations of disordered solids has been applied -- the technique of EXAFS -- under a variety of conditions: at low temperatures, under high pressures and at ambient conditions. Combined EXAFS and powder diffraction methods have been used to study the high pressure behavior of materials. The results revealed a complex picture of structural transformations in (GaSb)1-x(Ge2)x owing to the meta-stable nature of samples. The semiconductor-to-metal transition observed previously is found to be due to percolation through the high pressure metallic phase GaSb II. It is showed that the combination of two structural techniques, powder diffraction and EXAFS, can provide quite detailed information on the structural behavior of amorphous materials under high pressures. The temperature-dependent EXAFS studies showed that semiconducting amorphous GaSb is likely to be chemically ordered. Issues concerning determination of the structure of amorphous materials and information theory are widely discussed. (author)