The phenomenon of compound formation in Sn-based liquid alloys (MgSn and CuSn) has been discussed through the study of concentration-dependent thermodynamic and microscopic functions such as activity, excess free energy of mixing GMXS, concentration fluctuations in the long-wavelength limit Scc(0) and chemical short-range order (CSRO) parameters. The expressions for these functions have been obtained by using statistical mechanical theory based on compound formation. All the above-mentioned properties of mixing of MgSn and CuSn liquid alloys have been found to be asymmetric around equiatomic compositions. The larger negative values of GMXS and maximum deviation of Scc(0) from ideal values (Scc(0,id) at CMg = 0.66 in MgSn and at CCu = 0.75 in CuSn suggest that Mg2Sn and Cu3Sn compounds are formed in MgSn and CuSn systems, respectively. Our study of CSRO reveals that maximum order exists at compound-forming concentrations, i.e. CMg = 0.66 in MgSn and CCu = 0.75 in CuSn. It is also observed that the tendency for compound formation in MgSn is greater than that of the CuSn system, although the interactions in both systems are not very strong.
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