Oxidation and thermodynamic properties of Ag-Sn alloy

Diffused and reactive O atom in process of internal oxidation in Ag-Sn-O system was calculated by density functional perturbation approximation theory (DFPT). The results showed binding energy, enthalpy, heat capacity and Gibbs free energy of the phases in Ag-Sn-O system. O atom was on tetrahedron positions in Ag lattice. The system energy of O atom on the octahedron positions was 288.23 kJ·mol^-1 higher than that of O atom on the tetrahedron positions. However, Sn atom was on the replacement positions in Ag lattice. The order of cohesive energies (E_c) in Ag-Sn-O system was Ag ₆O₂>SnO₂>Ag₂SnO ₃>SnO>Ag₂O. The enthalpy of SnO₂ was -591.1 kJ·mol^-1, which was in agreement with experiment. SnO, Ag₆O₂, and Ag₂SnO₃ were the metastable phases in the normal temperature. Because the bonding ability of Sn-O was higher than that of Ag-O, there was no silver-oxide in Ag-Sn-O system. The heat capacity of Ag₂SnO₃ was much bigger than those of other compounds, and its Debye temperature was about 500 K. SnO₂ was the most stable phase in Ag-Sn-O system, which was showed by population analysis and Gibbs free energy.