Local atomic structure around Ni, Nb, and Zr atoms in Ni-Nb-Zr-H glassy alloys studied by x-ray absorption fine structure method

To elucidate hydrogen effects on the atomic configuration of Ni-Nb-Zr-H glassy alloys exhibiting proton-tunneling-induced Coulomb oscillation, we investigated the local atomic configuration around the Ni, Nb, and Zr atoms by x-ray absorption fine structure (XAFS) method. The analysis of the XAFS spectra indicates that there is the significant difference in structural response between the Zr 30 and the Zr 40 at. % alloys when hydrogen atoms are charged; charging the hydrogen atoms basically does not alter the local structures around the three atoms for the Zr 30 at. % alloy but induces the elongation of the Zr-Zr, Zr-Nb, and Nb-Ni distances for the Zr 40 at. % alloy. The distorted icosahedral Zr5 Ni5 Nb3 clusters assembled in randomly packed manners for the possible models in the Ni-Nb-Zr glassy alloy are proposed. The sites where hydrogen atoms occupy are also inferred.