'Shock Wave' Synthesis of Oxygen-Bearing Spinel-Type Silicon Nitride γ-Si_3(O,N)_4 in the Pressure Range from 30 to 72 GPa with High Purity

摘要

Silicon nitride, Si_3N_4 is a hard, refractory ceramic substance first synthesized more than 100 years ago. In the 1990s, its so-called α-modification was discovered to occur also as an exotic extraterrestrial mineral in certain chondrites and termed Nierite (Lee et al. 1995). The ambient-pressure modifications α-Si_3N_4 and β-Si_3N_4 have hexagonal (trigonal) lattice symmetry. β-Si_3N_4 crystallizes in the space group P6_3/m (Goodmann and O'Keefe 1980), α-Si_3N_4 in the space group P31c (Zhou et al. 1995). Both types consist of SiN_4 tetrahedra and N_3Si groups in a close-to-planar arrangement. In 1999 a high pressure modification of Si_3N_4 with spinel-type structure (space group Fd-3 m) and sixfold coodination of Si to nitrogen was discovered (ZERR et al. 1999). The γ-modification can be quenched to ambient conditions and shows a remarkable metastability and a high bulk modulus (Kuwabara et al. 2008; Jiang et al. 2001; Sekine et al. 2001; Sekine 2002). The excellent thermal and mechanical properties qualify γ-Si_3N_4 as an interesting candidate for high performance ceramics.