Thermodynamic properties of liquid Na-Sn alloys

The EMF of Na in liquid Na-Sn has been measured as a function of temperature using a concentration cell. The associated thermodynamic quantities of mixing such as free energy Delta G, entropy Delta S and enthalpy Delta H are obtained. A breakdown of Kopp's law, which expresses the additivity of specific heats, has been found. From the thermodynamic quantities obtained, the authors find that liquid Na-Sn alloys have two kinds of compound formation, NaSn and Na₃Sn. The curve for the concentration-concentration fluctuation S_cc(0) in the long-wavelength limit obtained from Delta G also supports the coexistence of these two compounds.