Preparation and High Temperature Phase Stability of La2O3–Y2O3–ZrO2 Composite Ceramic Nanopowder

4.5%Y2O3–ZrO2, 0.6%La2O3–YSZ, 0.8%La2O3–YSZ, 1.2%La2O3–YSZ (YSZ, 0.6La, 0.8La, 1.2La) (molar fraction) composite ceramic nanopowders were prepared by co–precipitation method using ZrOCl2·8H2O, Y(NO3)3·6H2O, La2O3 as raw materials. The synthesized powders were characterized and the phase stability was investigated. The results show that the size of 0.6La particles prepared by reverse titration method is ～20 nm, and the size of particles prepared by the straight titration method is ～50 nm. The agglomeration of the powder prepared by reverse titration method is also smaller than that of the powder prepared by straight titration method. After calcined at 600oC for 2 h, all of the synthesized powders showed the pure tetragonal structure; after sintered at 1200oC for 100 h, 0.6La, 0.8La showed the pure tetragonal structure, the cubic phase composed of both of YSZ and 1.2La and pyrochlore structure compose of 1.2La; after sintered at 1300  for 100 h, 0.6La, 0.8La, 1.2La showed the tetragonal structure, the cubic phase compose of all synthesized powders and pyrochlore structure compose of 1.2La and small fraction of monoclinic phase (～1.5%) was formed of YSZ; after sintered at 1400oC for 100h, the tetragonal phase cannot keep stable, monoclinic phase compose of all the synthesized powders, the monoclinic phase content of 0.6La, 0.8La, 1.2La, YSZ is 30.5%, 32%, 35%, 46.0% respectively. The phase stability of YSZ can be modified by addition small fraction of La2O3 at 1300oC.