Effects of ZrO 2 -La 2 O 3 co-addition on the microstructural and optical properties of transparent Y 2 O 3 ceramics

Commercial Y2O3 powder was used to fabricate Y2O3 ceramics sintered at 1600 °C and 1800 °C with concurrent addition of ZrO2 and La2O3 as sintering aids. One group with different contents of La2O3 (0–10 mol%) with a fixed amount of 1 mol% ZrO2 and another group with various contents of ZrO2 (0–7 mol%) with a fixed amount of 10 mol% La2O3 were compared to investigate the effects of co-doping on the microstructural and optical properties of Y2O3 ceramics. At low sintering temperature of 1600 °C, the sample single doped with 10 mol% La2O3 exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO2 and La2O3 co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800 °C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO2 and La2O3 single-doped samples. It was proved that the grain growth suppression caused by ZrO2 overwhelms the acceleration by La2O3. Meanwhile, 1 mol% ZrO2 acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y2O3 ceramic (1.2 mm in thickness) with 3 mol% of ZrO2 and 10 mol% of La2O3 sintered at 1800 °C for 16 h is 81.9% at a wavelength of 1100 nm, with an average grain size of 11.2 µm.