Abstract: An aluminum nitride sintered body having an oxygen concentration of not larger than 400 ppm, a metal impurity concentration of not larger than 150 ppm, and a carbon concentration of not larger than 200 ppm, and having an average crystal grain size of 2 ?m to 20 ?m. The sintered body exhibits particularly excellent optical properties such as an inclination of a spectral curve in the wavelength region of 260 to 300 nm of not smaller than 1.0 (%/nm), a light transmission factor of not smaller than 86% in the wavelength region of 400 to 800 nm, and a wavelength of not longer than 400 nm when the light transmission factor reaches 60% in the spectrum.

Abstract: An aluminum nitride sintered body comprising crystal grains of an average grain size (D50) of 0.1 to 2.5 ?m, and having a pore area ratio of not larger than 1×10?7, a pore density of not larger than 0.05 pores/mm2 of pores having diameters of not smaller than 1 ?m, and a Vickers' hardness in a range of 14 to 17 GPa. The aluminum nitride sintered body has a very small pore density despite of its relatively small crystal grain size, features excellent strength and mirror machinability, and is particularly useful as a material for circuit substrates on which fine wiring patterns are formed.

Abstract: An aluminum nitride sintered body having an oxygen concentration of not larger than 400 ppm, a metal impurity concentration of not larger than 150 ppm, and a carbon concentration of not larger than 200 ppm, and having an average crystal grain size of 2 ?m to 20 ?m. The sintered body exhibits particularly excellent optical properties such as an inclination of a spectral curve in the wavelength region of 260 to 300 nm of not smaller than 1.0 (%/nm), a light transmission factor of not smaller than 86% in the wavelength region of 400 to 800 nm, and a wavelength of not longer than 400 nm when the light transmission factor reaches 60% in the spectrum.