Fabrication and characterization of rare-earth doped sesquioxide laser ceramics

• Main Author: Wang, Jun
• Other Authors: Tang Dingyuan
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/73320
• Institution: Nanyang Technological University

Sesquioxide transparent ceramics such as Y 203, Lu203, and Sc203, have received a great attention as potential high powder solid-state laser hosts. To meet the laser applications requirements, porosity of the ceramics must be lower than 0.01 %. Densification of ceramics is closely related to quality of powders, sintering additives and sintering techniques. In the present research, comprehensive studies concerning the above factors are conducted in the view of ceramics science. Rare-earth ions doped Y203 po~ders have been synthesized by using solid-state reaction and chemical co-precipitation process, respectively. It was found that slurry concentration during ball milling affects the morphology and agglomeration degree of the powders, and thus influences the densification and grain growth of Y20 3 ceramics. However, it was difficult to completely eliminate the hard agglomeration by ball milling. In comparison, the powders synthesized by chemical co-precipitation process had more uniform particle size. Densification was strongly affected by both the agglomeration degree and the purity of powders. A~ the optimized calcination temperature of precursor (1300 °C), Y20 3 nanopowders with high purity and low degree of aggregation were obtained. Zr02, as the sintering additive, was effective in inhibiting the agglomeration of powders during the calcination. Meanwhile, it prevented the pore-boundary separation by solute drag mechanism during the sintering process. Reduction of the amount of sintering additives enhanced the thermal conductivity ofY20 3 ceramics. Grain boundary diffusion rate of Y 203 could be well controlled by co-doping with Zr02 and Ah03. Addition of a very small amount of Ah03 (81.8 wt ppm) enhanced densification and grain growth rate due to the activated sintering mechanism. Sintering method was equally important in terms of achieving full densification. Differentiate densification was prevented by using low heating rate or a three-step sintering process. Through optimizing the sintering maps (densification and grain growth) of Y 20 3 and Lu20 3 ceramics respectively, nearly full densification of the ceramics without sintering additives was achieved. Hot isostatic press (HIP) sintering provided a strong driving force for the densification of ceramics, thus sintering temperature could be greatly reduced and pore-boundary separation was prevented. Room temperature CW laser oscillations were demonstrated both on the 5 at.% Yb:Y20 3 and the 8 at.% Yb:Lu20 3 transparent ceramics fabricated in the project