Structural and electronic properties of crystalline and glassy calcium-zinc compounds. I. Trigonal prismatic ordering or tetrahedral close packing

Abstract

The authors present a detailed molecular dynamics study of the atomic structure of liquid and amorphous Ca-Zn alloys, based on inter-atomic forces derived from optimised first-principles pseudopotentials. In the Zn-rich limit, their results fit into the pattern characteristic for other sample-metal alloys; the liquid and the quench-condensed amorphous phase can be described as disordered tetrahedrally close packed. For the Ca-rich phases they find some distinctly different features; the most prominent is a pre-peak in the partial structure factor SZn-Zn(q) and in the number-density structure factor SNN(q), indicating topological short-range order. The analysis of the bond distances, coordination numbers and bond angles shows that the local order might be described as trigonal prismatic (distorted trigonal prisms of Ca, centred by Zn) in analogy to the trigonal prismatic structures of the crystalline intermetallic compounds Ca3Zn (Re3B-type), Ca5Zn3 (Cr5B3 type) and CaZn (CrB type).