Effect of 7YSZ on the long-term stability of YTaO4 doped ZrO2 system

The long-term stability of Ta0.16Y0.16Zr0.68O2 (TaYSZ) has been studied for possible application in thermal barrier coatings. X-ray diffraction was used for the characterization of the phase stability from 1100 to 1500 °C. Long-term stability of TaYSZ in presence of 7YSZ at 1250 °C has also been checked. At 1500 °C, TaYSZ remains as a single tetragonal phase. TaYSZ, however, when treated at 1250 °C for 600 h decomposes to m-ZrO2 and contains a minor YTaO4 phase and t-TaYSZ. In the presence of 7YSZ, decomposition of TaYSZ was suppressed. Decomposition of TaYSZ follows a different mechanism when treated in air and under vacuum. TaYSZ once pretreated at 1500 °C does not show any decomposition when treated at 1250 °C for 600 h, though weak reflections of Y3TaO7 are seen in the X-ray diffraction pattern. The onset of sintering and the coefficient of thermal expansion (CTE) of TaYSZ have been found to be ∼1200 °C and 11.24 × 10−6 K−1, respectively.