Patent ID: 8097550

Claim:
A spinel sintered body having a contrast ratio of 300 or more in the case of white light, where the contrast ratio is defined as the quotient obtained by dividing an amount of transmitting light in the case of being arranged between two polarizing plates, the polarizing directions of the two polarizing plates being parallel to each other, by an amount of transmitting light in the case of being arranged between two polarizing plates, the polarizing directions of the two polarizing plates being orthogonal to each other, wherein the spinel sintered body has a composition of MgO.nAl 2 O 3 , where n is 1.05 to 1.125, wherein the sintered body exhibits an in-line transmittance of 83% or more with respect to a light ray having a wavelength of 500 nm, and wherein the spinel sintered body has a thickness of 1 mm.