Densification of Yttria Transparent Ceramics: The Utilization of Activated Sintering

Highly transparent 0.5 at.% Tm:Y2O3 ceramics were prepared by using solid-state reaction combined with vacuum sintering method, with ZrO2 and Al2O3 as sintering aids. Doping amount of ZrO2 was fixed at 1 at.%, while the effect of Al2O3 on densification, microstructure evolution, and transmittance of the Y2O3 ceramics was carefully studied. It was found that the addition of Al2O3 was very effective in improving densification of Y2O3, due to the formation of an Al-rich eutectic phase Y4Al2O9 (YAM) during the sintering process. As the content of Al2O3 was increased from 0 to 81.8 wt ppm, porosity of the ceramics was decreased and transmittance was increased. However, when the content of Al2O3 was increased to 137 wt ppm, a secondary phase began to segregate at grain junctions. Further increase in the amount of Al2O3 led to an increase in both amount and size of the secondary phase. At the optimized content of Al2O3 with 81.8 wt ppm, the Tm:Y2O3 ceramics sintered at 1860 degrees C for 13 h exhibited an in-line transmittance of 83.0% at 2000 nm and 76.5% at 600 nm. It is expected that this finding can be readily applied to other transparent ceramics.