EXAFS OF DISORDERED SYSTEMS.

EXAFS is a new tool for structure detrmination of materials. It complements the standard diffraction techniques and opens up new possibilities for systems not amenable to other methods. In an application to amorphous Ge, EXAFS showed that its structure is a continuous random network and not a microcrystalline state. However, in transforming to the crystalline state amorphous Ge was found to pass through a mixed amorphous-microcrystalline state. The crystallization is a continuous transition extending over a T//S range of at least 70 degree C. Even at the highest T//S of 370 degree C the sample has not fully crystallized. EXAFS was able to discern the distinction between the microcrystalline and amorphous states because of high resolution due to its capability to detect data to higher k-values than diffuse x-ray scattering. This high resolution also led to a more accurate characterization of the first coordination shell relative to the crystalline state.