A diffraction investigation of some NiTa metallic alloy glasses

Abstract

X-ray and neutron diffraction measurements have been made on three NiTa metallic glasses, Ni55Ta45, Ni62Ta38 and Ni67Ta33. The total structure factors have been derived and the curves obtained with neutrons found to be particularly well defined. The total radial distribution functions (RDF) obtained are discussed in relation to models of close packing and to the stable crystalline phases in the NiTa alloy system. A derivation of the partial structure factors has been made for the Ni55Ta45 glass by an approximate method. The results of this suggest there is a progressively broadened distribution through the Ni-Ni, Ni-Ta and Ta-Ta first-neighbour distances which allows the form of the first peak in the total RDF to be understood. The broadening and expansion of particularly the Ta-Ta first-neighbour distances in the glassy state is consistent with the kind of local order which exists in the Ni2Ta and mu -NiTa crystalline phases. The possible identification of glassy NiTa alloys as disordered Frank-Kaspar phases, or alternatively as structurally relaxed 'soft sphere' assemblies, is discussed.