Thermodynamic and structural properties of Bi-based liquid alloys

Thermodynamic and microscopic structural properties of two Bi-based liquid alloys, such as In–Bi at 900 K and Tl–Bi at 750 K have been studied employing the regular associated solution model. We have estimated the mole fractions of the complexes and the free monomers assuming the existence of complexes In2BiIn2Bi in In–Bi melt and TlBiTlBi in Tl–Bi melt. The thermodynamic properties have been studied by computing the Gibbs free energy of mixing, enthalpy of mixing, entropy of mixing and activities of the monomers. The compositional contributions of the heat associated with the formation of complexes and the heat of mixing of the monomers to the net enthalpy change has also been studied. The structural properties of the liquid alloys have been studied by computing concentration fluctuation in the long-wavelength limit, chemical short-range order parameter and the ratio of mutual to intrinsic diffusion coefficients. For both of the alloy systems, the theoretical as well as the experimental values of SCC(0)SCC(0) are found to be lower than the corresponding ideal values over the whole composition range, indicating the hetero-coordinating nature of Bi–In and Bi–Tl alloy melts. All the interaction energy parameters are found to be negative and temperature dependent, and both the alloy systems are found to be weakly interacting.