LOCAL ORDER AND XAFS SPECTRA OF METAL METALLOID GLASSES

The study of local order in Ni-B and Fe-B model glasses by the Monte Carlo simulation method is presented. Despite the simple model for inter-atomic interaction used, the calculated radial distribution functions and generalized Warren chemical short-range order parameters are in quite reasonable agreement with high-resolution neutron diffraction data. Analysis of the bond-angle distribution indicates the existence of icosahedral motifs in the metal subsystem and the appearance of direct B-B contact in Ni66B34 glass with coordination number Z(BB) = 0.75 (the experimental value is Z(BB) = 0.9 +/- 0.1). The local order in glasses with ratio of components transition metal-metal (TM: M) equal to 80:20 and 66:34 changes noticeably under amorphisation and results in changes in x-ray absorption fine structure (XAFS) spectra. XAFS spectra appear to be sensitive to the local symmetry at the absorbing site and to higher-order coordination shells, especially around the metalloid atom. The calculated XAFS spectra may be used together with precise measurements to verify the structural models and provide information about the higher-order correlations.