Microstructure and optical properties of transparent aluminum oxynitride ceramics by hot isostatic pressing

Highly transparent aluminum oxynitride ceramic was fabricated by presintering at 1900 °C and further sintering by hot isostatic pressing (HIP) at 1900 °C under a 190 MPa argon atmosphere. For a 4.2 mm thick specimen doped with 0.1 wt.% Y2O3–La2O3, the inline light transmittance reached 78.8% at 600 nm and 84.4% at 1084 nm, respectively. Unlike the inhomogeneous microstructure of pressureless sintered specimen (grain size ∼150 μm), which contained substructure and twinning grains, the HIPed specimen had a homogeneous and refined microstructure with average grain size of ∼45 μm.