Thermochemistry of the ZrO₂–SrO System: From enthalpies of formation and heat capacities of the compounds to the phase diagram

The thermodynamics of the ZrO₂–SrO system is of interest for the optimization of synthesis and applications of functional materials and high-temperature structural ceramics. Earlier data on phase relationships and thermodynamic properties of the system are unfortunately scattered and inconsistent. In this study, the compounds Sr_n+1Zr_nO_3n+1 (n = 3, 2, and 1) were prepared by solid-state reaction. Their heat capacities from 573 to 1273 K were measured by differential scanning calorimetry and their enthalpies of formation from component oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. The CALPHAD method was used to assess the ZrO₂–SrO system, using both available literature data and our new measurements. A self-consistent thermodynamic database and the calculated phase diagram of the ZrO₂–SrO system are provided. This work is a prerequisite for accurate predictions of the relationships among the composition, temperature, and microstructure of complex functional and structural materials containing ZrO₂ and SrO.