Silicon nitride sintered material and production prodess thereof

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The silicon nitride sintered material of the present invention contains silicon nitride, a Group 4a through 6a element, a rare earth element, and silicon carbide, and is characterized in that the amount of the rare earth element as reduced to a certain oxide thereof is 5.7-10.3 mol%; the ratio by mol of subtraction remainder oxygen amount as calculated in relation to the oxygen contained in the sintered material, the remainder oxygen amount being expressed in terms of silicon dioxide, to the amount of oxygen contained in the sintered material is at least 0.50 and less than 0.70; a four-component crystalline phase of rare earth element - silicon - oxygen - nitrogen is not present; and the thermal expansion coefficient is at least 3.7 ppm/ DEG C between room temperature and 1, 000 DEG C.