Anisotropic alumina ceramics with isotropic optical properties

Excellent mechanical and isotropic optical properties are achieved simultaneously from fully dense polycrystalline advanced alumina ceramics with a hexagonal crystal structure, which optically anisotropic. A small amount (240 ppm) of ZrO2 additive is used to synthesize the transparent an average grain size 0.7 µm, locally detected distortion (birefringence) extremely minimized, less than 20 nm/pass. Total transmittance (86%) (thickness = 0.3 mm) in ultraviolet (UV) infrared (IR) regions similar that commercial c-axis sapphire single crystals produced by Czochralski (CZ) method, while extinction ratio visible wavelength area over 25 dB. Like glass crystals, can clearly display texts images on liquid (LCD) screens. boundary phase nano-sized Al2O3–ZrO2 composition (amorphous) formed at ceramics, enhances four-point bending strength fracture toughness (KIC) 921 MPa 6.8 MPa·m0.5, respectively, hence superior those crystals.