Phase Diagram Calculations for ZrO2 Based Ceramics: Thermodynamic Regularities in Zirconate Formation and Solubilities of Transition Metal Oxides

Phase diagram calculations have been made using evaluated or estimated thermodynamic properties of stoichiometric compounds and solid solutions in the ZrO₂ – MO (M = Mg, Ca, Sr), the ZrO₂ – M’O_1.5 (M’ = Sc, Y, La, Rare earth) and the ZrO₂ – M”O₂ (M” = Ti, Hf, Ce) systems. An emphasis has been placed on finding thermodynamic regularities in the stability of perovskites, pyrochlore–type compounds, and fluorite–type solid solutions. Interaction parameters for the fluorite solid solutions have been found to be well correlated with ionic radii. This has been utilized to calculate the solubilities of the transition metal oxides into Y₂O₃–stabilized ZrO₂ (YSZ). An associated solution model has been adopted to derive the respective contributions from the various valence states of the transition metal ions as functions of temperature and oxygen potential.