| Abstract Scope |
Excellent mechanical and isotropic optical properties are achieved simultaneously from fully dense polycrystalline advanced alumina ceramics with a hexagonal crystal structure, which are optically anisotropic. A small amount additive is used to synthesize the transparent alumina ceramics with sub-micron grain size, and locally detected optical distortion (birefringence) is extremely minimized, less than 20 nm/pass. Total transmittance (86%) of alumina ceramics (thickness = 0.3 mm) in ultraviolet to infrared regions is similar to that of commercial c-axis sapphire single crystals produced by Czochralski method, while the extinction ratio in the visible wavelength area is over 25 dB. Like glass and the c-axis sapphire single crystals, the alumina ceramics can clearly display texts and images on liquid crystal display (LCD) screens. |