Transparent polycrystalline nanoceramics consisting of triclinic Al 2 SiO 5 kyanite and Al 2 O 3 corundum

Transparent polycrystalline nanoceramics consisting of triclinic Al 2 SiO 5 kyanite (91.4 vol%) and Al 2 O 3 corundum (8.6 vol%) were fabricated at 10 GPa and 1200‐1400°C. These materials were obtained by direct conversion from Al 2 O 3 ‐SiO 2 glasses fabricated using the aerodynamic levitation technique. The material obtained at 10 GPa and 1200°C shows the highest optical transparency with a real in‐line transmission value of 78% at a wavelength of 645 nm and a sample‐thickness of 0.8 mm. This sample shows equigranular texture with an average grain size of 34 ± 13 nm. The optical transparency increases with decreasing mean grain size of the constituent phases. The relationship between real in‐line transmission and grain size is well explained by a grain‐boundary scattering model based on a classical theory.