Abstract: La₂O₃-Y₂O₃-ZrO₂ (LaYSZ) green composite ceramic powder was prepared by converse chemical coprecipitation method. The powder was conglomerated and heattreated to be suitable for plasma spraying. The chemical compositions, microstructures, flowability and apparent density, phase stability at high temperatures were analyzed by means of inductively coupled plasma-atomic emission spectrometre (ICP-AES), scanning electron microscope (SEM), hall flowmeter, X-ray diffraction, respectively. The results show that the green composite powder presents tetragonal ZrO₂ phase structure at room temperature. After heat-treated at 1150℃ for 2h, the conglomerated powder with spherical shape and dense surface exhibits good flowability, which can be used for plasma spraying. After heat-treated at 1300℃ for 100h, LaYSZ still keeps single tetragonal ZrO₂ structure, while 12mol% tetragonal phase of 8YSZ transforms to monoclinic phase. After heat-treatment at 1400℃ for 100h, the amount of monoclinic phase in LaYSZ is of 2mol%, and that in the 8YSZ is of 47mol%. It shows that La₂O₃, Y₂O₃ co-doped ZrO₂ exhibits better phase stability than single Y₂O₃-doped ZrO₂.

Key words: thermal barrier coating, La₂O₃-Y₂O₃-ZrO₂, chemical coprecipitation, phase stability