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Dense ␤-Si 3 N 4 with various Y 2 O 3 /SiO 2 additive ratios were fabricated by hot pressing and subsequent annealing. The thermal conductivity of the sintered bodies increased as the Y 2 O 3 /SiO 2 ratio increased. The oxygen contents in the ␤-Si 3 N 4 crystal lattice of these samples were determined using hot-gas extraction and electron spin resonance techniques. A good correlation between the lattice oxygen content and the thermal resistivity was observed. The relationship between the microstructure, grain-boundary phase, lattice oxygen content, and thermal conductivity of ␤-Si 3 N 4 that was sintered at various Y 2 O 3 /SiO 2 additive ratios has been clarified.

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Since the confirmation that nonmetallic single crystals with a diamond-like structure, such as SiC, BP, and AlN, have high intrinsic thermal conductivities of over 300 W m−1 K−1,1,2 a great deal of effort has been focused on the development of nonoxide polycrystalline ceramics with high thermal conductivity.