Lattice spacing relationships in hexagonal close-packed silver-zinc-manganese alloys

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Abstract
The lattice spacings of close-packed hexagonal ε-phase alloys in the ternary system silver-zinc-manganese have been determined as a function of alloy composition, using x-ray powder methods. The observed trends in the lattice spacing/composition curves are interpreted according to the established models for the interactions between the Fermi surface and the Brillouin zone faces. In particular the observation that the axial ratio of manganese-zinc alloys is less than 1·633 for all compositions is thought to be due to the (1010) zone faces being overlapped, while the reversal in slope of the c-spacing/composition curve at about 84 at. % zinc for silver-zinc-1% manganese alloys, is attributed to the onset of overlap of Fermi electrons across the (0002) zone boundaries. Effective valencies of metallic manganese in solid solution in these alloys have been deduced for alloys within the ternary phase field by the method discussed by Cockayne and Raynor (1961) and Henderson and Raynor (1962a). It is suggested that in alloys having electron concentrations greater than 1·75, manganese has a negative valency, i.e. manganese absorbs electrons from the valence band. The variations in valency are discussed in terms of the existence of virtual bound 3d states associated with the manganese atoms, and the transference of electrons to or from these states as a result of changes in the electron concentration or lattice spacings of the alloys.