Oxygen Content in ß‐Si3N4 Crystal Lattice

β-Si 3 N 4 crystals were obtained through the heat treatment of α-Si 3 N 4 powder with additives, Y 2 O 3 :SiO 2 = 1:2 and 2:1, and subsequent acid treatments that removed the secondary phases. The lattice oxygen contents of these crystals were determined by the hot-gas extraction method to be 0.258 ± 0.006 and 0.158 ± 0.003 wt% for the additive compositions of Y 2 O 3 :SiO 2 = 1:2 and 2:1, respectively. The oxygen dissolved in the β-Si 3 N 4 crystal lattice as much as in the α-Si 3 N 4 crystral lattice prepared by the chemical vapor deposition process and in the AIN crystal lattice that exhibited high thermal conductivity.