Structural origins of the excellent glass forming ability of Pd ₄₀Ni ₄₀P ₂₀

We report a hybrid atomic packing scheme comprised of a covalent-bond-mediated "stereochemical" structure and a densely packed icosahedron in a bulk metallic glass Pd ₄₀Ni ₄₀P ₂₀. The coexistence of two atomic packing models can simultaneously satisfy the criteria for both the charge saturation of the metalloid element and the densest atomic packing of the metallic elements. The hybrid packing scheme uncovers the structural origins of the excellent glass forming ability of Pd ₄₀Ni ₄₀P ₂₀ and has important implications in understanding the bulk metallic glass formation of metal-metalloid alloys.