Abstract: The lattice parameters a and the molar volumes V_m of Pb-based a-phase solid solution in the Pb-Sn-Cd ternary system were determined by means of X-ray diffraction. The lattice parameters a vary linearly with the molar fractions, the lattice distortion is mainly affected by the size effect of components. The molar volumes show a positive deviation from the behavior of the ideal solution, and the contribution of the solute Cd to excess molar volumes V^E is much larger than that of the solute Sn. According to Vegard's law-or sub-regular solution model, the relationship between a or V_m and the compositions of alloy is obtained by the mathematic regressive method, the prediction precisions of both the formulae are within the limits of experiment error.

Key words: Alloy solid solution, Lattice parameter, Molar volume, Excess molar volume