The apparent metallic valencies of transition metals in solid solution

Abstract

According to previous work, solution of a third metal in the close-packed hexagonal ζ-phases which occur at approximately 1.5 electrons per atom in certain binary copper alloys causes the lattice spacings to vary in such a way that the axial ratio remains constant at a constant valency electron:atom ratio. On the assumption that this remains true when the third metal is a transition metal of the Vlllth Group of the Periodic Table, the lattice spacings of solutions of manganese, iron, cobalt and nickel in the copper-germanium ζ-phase have been examined. From the observed axial ratios, the contributions of the transition metals to the conduction band of the alloy have been assessed and expressed as an effective valency value. This value, at the lower electron:atom ratios (approximately 1.39), is unity for iron, cobalt and nickel, but decreases as the electron:atom ratio rises. For manganese effective valency values at the lower electron:atom ratios vary from 1.64 to 1.42 according to manganese content; again the values decrease with increasing electron:atom ratio. The dependence of the effective valency values on transition metal content is such that, if a lattice contraction is produced by the solution of the transition metal in the binary ζ-phase (cobalt, nickel) the valency decreases as the transition metal content rises. Lattice expansion (manganese) leads to the reverse effect, while the effective valency of iron, which has little effect on the lattice spacings, is virtually independent of iron content. The results are discussed in terms of transfer of electrons between the conduction band of the alloy and the virtual bound 3dstates localized on the transition metal atoms in solution.