Thermodynamic study of some solid solutions in the CaOZrO2 system by emf method

The thermodynamic properties of some solid solutions in the CaOZrO₂ system have been investigated by using solid electrolyte galvanic cells of the type: O₂, Pt|CaO, CaF₂|CaF₂ (t_F = 1)| δCaO(1 ? δ)ZrO₂, CaF₂|Pt, O₂. The influence of CaF₂ added in electrodes on the thermodynamic equilibrium was investigated. It was shown that the heterogeneous field with cubic solid solution reaches the composition x = 0.17 mole of CaO. The results indicate that addition of ZrO₂ to the saturated solid solution produces a significant decrease in the activity of CaO. Measured data were used to calculate thermodynamic parameters of reactions with saturated solid solutions Ca_0.17 Zr_0.83 O_1.83, ZrO₂, and CaZrO₃. At temperatures below 820°C, saturated solid solutions have a tendency to decompose into CaZrO₃ and ZrO₂. A comparison of the thermodynamic results with available data on phase relationships in the CaOZrO₂ system is presented. High thermodynamic stability of SrZrO₃ and BaZrO₃ is one of the reasons for the absence of cubic solid solutions in the system MeOZrO₂ (MeSr, Ba).