To obtain a sintered compact having excellent heat radiation characteristics and reliability, comprising silicon nitride in a specific ratio, one or more kinds of yttrium and a lanthanoid group element and one or more kinds of Hf, Ti and Zr, making SiO2 content and aluminum content of sintered compact having plural grain boundary crystal phases have specific values or smaller than them and heat conductivity have a specific value or larger it.
This silicon nitride sintered compact comprises 90-99 mol.%; of silicon nitride, 1-10 mol% calculated as oxide (Re203) of one or more kinds of Y and Lu group elements and 0-4 mol% calculated as MO2 of one or more kinds of Hf, Ti and Zr, has the molar ratio of SiO2/(Re2O3+SiO2) of ≤0.5 and ≤1,000 ppm aluminum content, the ratio of the total of the main peak intensity of phase H, Re2SiO5 and Re2Si207 to the total of the main peak intensity of phase K, phase J, Re2Si3O3N4 and Re2O3 of ≤1.0 and ≥90 W/(m.K) heat conductivity.
YOKOTA HIROSHI
IBUKIYAMA MASAHIRO
TOKURA KAZUYUKI
