Thermochemical properties and phase transitions of Ba–Sn alloys from thermal characterization and emf measurements

Thermodynamic properties of Ba–Sn alloys were determined for Ba mole fractions (x_Ba = 0.03–0.69) by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and electromotive force (emf) measurements. Six intermetallic compounds (BaSn₅, BaSn₃, Ba₃Sn₅, BaSn, Ba₅Sn₃, and Ba₂Sn) were identified by XRD and the phase transition temperatures were determined by DSC up to x_Ba = 0.50, which were used to delineate phase boundaries for constructing an experimentally-determined phase diagram. In addition, thermochemical solution properties were calculated by measuring emf values of Ba–Sn alloys using the following electrochemical cell: Ba(s) | CaF₂–BaF₂ | Ba(in Sn) over 713–1063 K, including activity and partial molar quantities of Gibbs energy, entropy, and enthalpy. The activity of Ba in Sn was as low as 1.5 × 10⁻¹¹ at x_Ba = 0.03 and 923 K, indicating highly non-ideal solution behavior with a large excess partial molar Gibbs energy (−164 kJ mol⁻¹). By integrating solution properties from emf measurements with the phase behavior by DSC and XRD, a reliable description of the Ba–Sn system was established.