Thermodynamic study of some solid solutions in the CaOZrO 2 system by emf method

The thermodynamic properties of some solid solutions in the CaOZrO ₂ system have been investigated by using solid electrolyte galvanic cells of the type: O ₂, Pt|CaO, CaF ₂|CaF ₂ ( t_F = 1)| δCaO(1 - δ)ZrO ₂, CaF ₂|Pt, O ₂. The influence of CaF ₂ 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 ZrO ₂ 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, ZrO ₂, and CaZrO ₃. At temperatures below 820°C, saturated solid solutions have a tendency to decompose into CaZrO ₃ and ZrO ₂. A comparison of the thermodynamic results with available data on phase relationships in the CaOZrO ₂ system is presented. High thermodynamic stability of SrZrO ₃ and BaZrO ₃ is one of the reasons for the absence of cubic solid solutions in the system MeOZrO ₂ ( MeSr, Ba).