On the origin of second-peak splitting in the static structure factor of metallic glasses

It is proposed that the splitting of the second peak of the total static structure factor, S(k), of many metallic glasses is essentially the same feature as the indentation at kσ = (9/2)π in the function (sin k σ + α−1 sin kασ), caused by the coincidence of the fourth minimum of the second term with the third maximum of the first term when α ≈ 5/3. Together with the strong-weak relation of the split peak components of S(k), this feature indicates the splitting to be direct evidence for face-sharing of regular tetrahedra (α = 2√2/3) dominating the topological short range order; increasing the number of face-sharing tetrahedra in local structural units indeed increases the amount of peak splitting in S(k); a dense random packing of well defined identical structural units (DRPSU), with neighbouring units linked together by a shared icosahedron, is described in detail. The packing fraction in a homogeneous, isotropic 1078-atom model is 0.67, after static relaxation under a two-body Lennard-Jones potential.