Partial Atomic Volume of Early Transition Metals in A10 Metal-Based Solid Solutions

Unit-cell parameters were measured for the A 10 metal-based (= Ni, Pd, Pt) solid solutions (Pearson symbol cF4, space group Fm3m, Cu type) with the A 5 transition metals (V, Nb, Ta) in the whole range of homogeneity. Composition dependence both of the average atomic volume and the enthalpy of formation were investigated for the A 10 metal-based solid solutions with the A 5 and A 6 transition metals; the partial atomic volume and the partial molar enthalpy of formation of the A 5 and A 6 transition were determined for the A 10 -rich terminal phases. Among the systems investigated, only the solid solutions Pd(Cr) and Pt(Cr) show partial atomic volume of chromium larger than the chromium atomic volume. In the nickel-based solid solution, the partial atomic volume of chromium is equal to the chromium atomic volume. The partial molar enthalpy of formation for the A 5 transition metals - in the nickel, palladium and platinum-rich alloys - shows larger negative values than values evaluated for the A 6 transition metals. An enlarged investigation of the data available in literature shows that both the relative volume change, resulting from the dissolving process of the early transition metals in the A 10 metal-based alloys, and the negative values of the partial molar enthalpy of formation increase with decreasing number of the 3d and 4d electrons of the early transition elements. For the 5d quasihomologous transition metals, this observation is valid for the A 4 ... A 6 elements as well.