EXAFS Studies of La-Ga Metallic Glasses

Abstract

Extended X-ray Absorption Fine Structure ( EXAFS ) measurements have been performed on the Ga edge of several La-Ga metallic glasses, using an in-lab spectrometer. The results obtained are compared with earlier experiments on the same materials where X-ray diffraction and isomorphous substitution were used to determine partial pair correlation functions. This is, therefore, a rigorous test of the EXAFS technique when applied to strongly disordered systems, such as metallic glasses. It is found that the glass La80Ga20 has a comparatively simple local Ga environment and that the EXAFS for this glass can be described very well with a single asymmetric shell of La atoms surrounding the Ga. As the Ga concentration is increased, however, it is found that the local Ga environment becomes more complicated. Traditional methods of EXAFS analysis, based on nonlinear least squares curve fitting, are then unable to distinguish between several different possible local Ga environments. Finally a new, essentially non-parametric, method of analyzing EXAFS data is discussed and tests are conducted to demonstrate the circumstances under which this new method could prove advantageous over the more traditional methods.