Enthalpy and Heat Capacity of Liquid Cs–Bi Alloys

This work presents a summary and analysis of previously published data on the enthalpy and heat capacity of liquid Cs–Bi alloys containing 20.0, 27.1, 40.0, 50.0, 57.0, and 66.65 at % of bismuth. The enthalpy increment data were obtained using a high-precision isothermal drop calorimeter, with an error not exceeding 0.3%. It is shown that the heat capacity of liquid Cs–Bi alloys significantly exceeds the heat capacity of the individual components. As the temperature increases, the heat capacity of the melts gradually approaches that of an ideal solution. The concentration dependence of the heat capacity of the liquid Cs–Bi system exhibits a pronounced maximum in the range of 20 to 50 at % of Bi. The enthalpy of mixing, on the other hand, is negative, and its concentration dependence shows a minimum in the same composition range. The observed features in the behavior of the caloric properties support the hypothesis proposed by several authors that the structure of Cs–Bi melts exhibits a tendency to form ionic complexes in the form of chains of varying lengths composed of bismuth anions surrounded by cesium cations, with the concentration of these complexes reaching a maximum at certain stoichiometric compositions.