Effect of yttrium-doped grain boundary on sintering behavior and properties of transparent ZnAl2O4 ceramics

Pore-closed ZnAl2O4 ceramic can hardly be pressureless sintered from conventional (>100 nm) powder, which restricts the fabrication of the transparent ceramic by capsule-free hot isostatic pressing technique. This work focused on the effect of yttrium-doping on the microstructural evolution in the sintering of a ~180-nm ZnAl2O4 powder. At a concentration of 300 or 600 ppm, the yttrium ions segregated along the grain boundaries and contributed to ordered nanostructures, which could suppress abnormal grain growth in both air sintering and hot isostatic pressing. The optimized Y-doped ZnAl2O4 transparent ceramic owned good visible light transmittance (>65%) and a wide transmission range (6.0 μm at the 60% transmittance) at a thickness of 1.5 mm, as well as high thermal conductivity (24.9 W·m-1·K-1) and reasonable mechanical properties (Vickers hardness of 12.9 GPa and Young's modulus of 281.3 GPa), meeting the application requirements for infrared windows.