Densification of Yttria Transparent Ceramics: The Utilization of Activated Sintering

Highly transparent 0.5 at.% Tm:Y 2 O 3 ceramics were prepared by using solid‐state reaction combined with vacuum sintering method, with ZrO 2 and Al 2 O 3 as sintering aids. Doping amount of ZrO 2 was fixed at 1 at.%, while the effect of Al 2 O 3 on densification, microstructure evolution, and transmittance of the Y 2 O 3 ceramics was carefully studied. It was found that the addition of Al 2 O 3 was very effective in improving densification of Y 2 O 3 , due to the formation of an Al‐rich eutectic phase Y 4 Al 2 O 9 ( YAM ) during the sintering process. As the content of Al 2 O 3 was increased from 0 to 81.8 wt ppm, porosity of the ceramics was decreased and transmittance was increased. However, when the content of Al 2 O 3 was increased to 137 wt ppm, a secondary phase began to segregate at grain junctions. Further increase in the amount of Al 2 O 3 led to an increase in both amount and size of the secondary phase. At the optimized content of Al 2 O 3 with 81.8 wt ppm, the Tm:Y 2 O 3 ceramics sintered at 1860°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.