Control of the nanostructure of MgO–Y2O3 composite ceramics using two-step sintering for high temperature mid infrared window applications

Transparent Y2O3–MgO nanocomposite ceramic has been processed for mid-IR window applications. The powder was synthesized by a sol-gel route. The final temperature of this process has an impact on the crystallite size and crystallization ratio. A homogeneous powder with around 10 nm crystallite size was made with a final temperature of 600 °C. The powder was then sintered by the SPS technique performing a two-step sintering process at 1200 °C/50 MPa instead of a conventional bearing. A fully dense ceramic (>99%) with an average grain diameter of 150 nm (compared to 350 nm with one-stage sintering) was obtained. After HIP at 400 MPa and annealing in air for 100 h post-treatments, the IR transmittance in the 3–5 μm wavelength range exceeds 80% for a thickness of 1 mm. Transparency loss at 5 μm is less than 10% at 1000 °C, which is more suitable for the IR's band II than materials such as sapphire, spinel or AlON.