Experimental phase equilibria in the ZrO2-YbO1.5-TaO2.5 system at 1500 °C and the melting temperatures in the quasi-binary ZrO2-YbTaO4 system

Phase equilibria of oxide ceramics play an important role in the design of innovative thermal barrier coatings. In this work, the isothermal section at 1500 °C of the ZrO 2 -YbO 1.5 -TaO 2.5 (ZYbTO) system was investigated by means of X-ray diffractometer, scanning electron microscopy and Raman spectroscopy, using thirteen samples. Two three-phase equilibria were accurately determined. Ternary fluorite in the ZYbTO system was found to form a continuous solid solution from binary ZrO 2 -YbO 1.5 to binary YbO 1.5 -TaO 2.5 . Both ternary and t-ZrO 2 phases roughly extend along the Yb:Ta=1 ratio line. The maximum solubility of YbO 1.5 and TaO 2.5 co-dopants in t-ZrO 2 was determined to be about 58.0 mol%, and the compositional boundary between transformable and non-transformable tetragonal zirconia was deduced to be approximately 70 mol% ZrO 2 . The maximum ZrO 2 solubility in ternary was found to be roughly 26.4 mol%. Moreover, the phase diagram of the ZrO 2 -YbTaO 4 quasi-binary system was established from the cooling curve analysis, identifying a eutectic reaction of Liquid→ZrO 2 +YbTaO 4 at about 1885 °C and a composition of around 32ZrO 2 -33YbO 1.5 -35TaO 2.5 . This study provides a foundation for thermodynamic assessment of the ZrO 2 -YbO 1.5 -TaO 2.5 system, supporting the design and development of related ceramic materials.