Effect of doping oxides on the structure stability and sintering properties of ZrO₂ phase

ZrO₂ powders and ceramics doped with Y₂O₃ and Al₂O₃ respectively were prepared by a copreeipitation-gel method using low temperature calcining and medium temperature sintering. The structure stability and sintering properties of ZrO₂ phase doped with the different oxides were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that calcined at 870℃ for 15 min, ZrO₂ powders doped with Y₂O₃ of 5% in molar fraction have a cubic phase, but those doped with Al₂O₃ of 5% in molar fraction have a tetragonal phase. After sintering the formed powders at 1 400℃ for 4 h, the former remains the cubic phase at room temperature, but the latter has a monoclinic phase. In the calcining powders, Al³⁺ dissolves into the lattice of ZrO₂ and stabilizes the ZrO₂ tetragonal lattice; whereas in their ceramic, Al³⁺ diffuses from the ZrO₂ lattice to the grain boundaries, so it can not afford a stabilizing effect on the ZrO₂, only plays a role in promoting the sintering and thinning grain.