Theoretical computation of coherent scattering intensities, partial structure factors, and diffusion coefficients of magnesium-bismuth melt

The magnesium-bismuth alloy consisting of the peculiar metal bismuth, which shows a conspicuous right-hand shoulder in the structure factor, has been studied with a square-well potential as a perturbation over a hard-sphere mixture. The partial structure factors $S_{11}$(K), $S_{12}$(K), and $S_{22}$(K) and also $S_{\mathrm{NN}(\mathrm{K}}$), $S_{\mathrm{CC}(\mathrm{K}}$), and $S_{\mathrm{NC}(\mathrm{K}}$) (the number-number, concentration-concentration, and cross-correlation functions, respectively) have been computed at various concentrations and temperatures. The total structure factors have been computed. The alloy containing 30% of bismuth for which experimental data is available has been compared and the agreement is excellent. The alloy is found to show segregation tendency of its constituents and this is exhibited in the subsidiary peak that comes with increased concentration of bismuth in $S_{\mathrm{NC}(\mathrm{K}}$). The compressibilities at various concentrations of bismuth have been computed from the Kirkwood-Buff formula while the diffusion coefficients have been computed from the linear-trajectory principle for mixtures.