X-RAY-ABSORPTION FINE-STRUCTURE OF THE MODEL AMORPHOUS AND CRYSTALLINE NI2B ALLOY

Studies of the effect of amorphisation on the local order and X-ray ab sorption fine structure as a probe for higher correlations are present ed for the crystalline and amorphous alloys Ni2B. The Ni2B alloy has a trigonal prismatic order in the crystalline state without direct B-B contact. The amorphous alloy has a B-B coordination number Z(BB) = 0.9 +/-0.1. Full multiple-scattering calculations of the XAFS spectra have been performed to reveal the effect of amorphisation and the possible sensitivity of the near edge structure to higher-order correlations. To account for the important changes in the electronic structure, LMTO calculations of the electronic structure have been performed for crys tals and recursion-TB-LMTO calculations have been performed for the am orphous phase. The present calculations have shown that the high low-e nergy B K-edge peak seen in c-Ni2B is the result of scattering from th e first Ni shell. and it is almost washed out in the amorphous phase. The resulting form of the XAFS spectrum at energies < 40 eV is determi ned by complex scattering events. The deformation of the Ni K-edge is less pronounced.