Short-range structure of amorphous metal-metalloid alloys

Abstract

The structure of amorphous alloys is interpreted either by the models of dense random packed spheres or by quasi-crystalline models. Experimental data like density, pair distribution function (PDF), average hyperfine field distribution act as critical test for structure models and give indications of how they may be improved. In the case of amorphous metal-metalloid alloys it could be shown, that disordered models with short-range order of the crystalline Ni 3P-phase provide PDFs in agreement with experimental ones. As an important parameter the fraction of metalloid atoms has to be introduced in binary structure models. Models with crystal-like short-range order requires some plausible assumptions to include different chemical compositions. The model PDFs of amorphous Fe 1− x B x with Ni 3P short-range order were calculated assuming the exceeding metal atoms to be situated at metalloid place. Clusters with Ni 3P short-range order were produced and relaxed using Lennard-Jones potentials. The total PDFs show the following behaviour with decreasing metalloid fraction: 1. 1)nearest neighbour distance decreases; 2. 2)coordination number increases; 3. 3)first component of the second split peak decreases. These model calculations are in agreement with experimental results and confirm the existence of a short-range order in this class of amorphous alloys similar to that in the crystalline unit cell.