Compositions in the ZrO2-Y2O3-Ta2O5 system are of interest for new high performance thermal barrier coating applications due to their promising high-temperature properties. Alongside an extended tetragonal phase field stable to temperatures at least up to 1500 °C obtained by equimolar co-doping of Y3+ and Ta5+, the YTaO4 phase field recently attracted attention. Both phase fields of interest lie on the ZrO2-YTaO4 quasibinary investigated in this work.
For high temperature applications, it is essential to understand phase stabilities and relations as well as energies and driving forces of the stable and metastable phases. Experimental and computational thermodynamics using the CALPHAD method gives a self-consistent description of the materials system, facilitating materials development. In this work, the energetics and phase stabilities of the ZrO2-YTaO4 quasibinary were investigated experimentally. The enthalpies of formation of different phases as a function of composition were determined using high-temperature oxide melt solution calorimetry. Transition temperatures, enthalpies of transition and phase stabilities were explored by several thermal analysis techniques, e.g. differential thermal analysis (DTA), measurement of cooling traces using laser melting and high-temperature in-situ X-ray diffraction. The results will be used for CALPHAD modeling to obtain a comprehensive understanding of the thermochemistry of the quasibinary.