Abstract
In the pseudo binary system ZrO2-YOF included in the ZrO2-YF3-YO1.5 ternary system, samples of 3.0-7.7 mol% YOF within the region of tetragonal single phase at 1300°C were isostatically hot-pressed at 1200°, 1300°and 1450°C under 200 MPa for 3 h after encapsulating into Pt capsule to avoid compositional changes. Only for ZrO2-7.7 mol%YOF, metastable tetragonal zirconia single phase was obtained as a sintered body. For the other samples (<7.7 mol% YOF) whole or most of the tetragonal phase transformed diffusionlessly to monoclinic phase during cooling.X-ray study showed that the unit cell of the tetragonal phase has larger axial ratio (c/a), and that of the monoclinic phase was more distorted (larger P) than that in the ZrO2-YO1.5 system. According to the measurement by DTA on encapsulated specimens, the tetragonal phase in the ZrO2-YOF system transformed at higher temperatures than that in the ZrO2-YO1.5 system. This seems to be caused by more distorted cells of the tetragonal and the monoclinic phases as the result of F- doping. Stress induced transformation was confirmed for the metastable tetragonal phase of this YOF doped zirconia.
