Patent ID: 8586493

Claim:
A silicon nitride sintered body, consisting of crystal grains of β-type silicon nitride and a grain boundary phase containing at least one type of rare earth element (RE), magnesium (Mg) and silicon (Si), wherein: the grain boundary phase comprises an amorphous phase and a MgSiN 2 crystal phase; the X-ray diffraction line peak intensity of any crystal plane of a crystal phase containing the rare earth element (RE) is less than 0.0005 times the sum of the diffraction peak intensities of (110), (200), (101), (210), (201), (310), (320) and (002) of the crystal grains of the β-type silicon nitride; the X-ray diffraction peak intensity of (121) of the MgSiN 2 crystal phase is 0.0005 to 0.0019 times the sum of the X-ray diffraction peak intensities of (110), (200), (101), (210), (201), (310), (320) and (002) of the crystal grains of the β-type silicon nitride, and the silicon nitride sintered body contains magnesium (Mg) with 6.7 to 9.9 mol % of magnesium oxide (MgO), and at least one type of rare earth element (RE) with 1.2 to 2.3 mol % of rare-earth element oxide (RE 2 O 3 ), the total amount of MgO and RE 2 O 3 contained is 7.9 to 12.2 mol %, and a molar ratio of (RE 2 O 3 )/(MgO) is 0.1 to 0.3.