Effect of doping oxides on the structure stability and sintering properties of ZrO ₂ phase

ZrO ₂ powders and ceramics doped with Y ₂O ₃ and Al ₂O ₃ respectively were prepared by a coprecipitation-gel method using low temperature calcining and medium temperature sintering. The structure stability and sintering properties of ZrO ₂ 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°C for 15 min, ZrO ₂ powders doped with Y ₂O ₃ of 5% in molar fraction have a cubic phase, but those doped with Al ₂O ₃ of 5% in molar fraction have a tetragonal phase. After sintering the formed powders at 1400°C for 4 h, the former remains the cubic phase at room temperature, but the latter has a monoclinic phase. In the calcining powders, Al ³⁺ dissolves into the lattice of ZrO ₂ and stabilizes the ZrO ₂ tetragonal lattice; whereas in their ceramic, Al ³⁺ diffuses from the ZrO ₂ lattice to the grain boundaries, so it can not afford a stabilizing effect on the ZrO ₂, only plays a role in promoting the sintering and thinning grain.