Shock-induced transformation of beta-Si3N4 to a high-pressure cubic-spinelphase

beta-Si3N4 powders were shock compressed and quenched from 12 to 115 GPa. b eta-Si3N4 transforms to the spinel-type Si3N4 (c-Si3N4) by a fast reconstru ctive process at pressures above about 20 GPa. The yield of c-Si3N4 recover ed from 50 GPa and about 2400 K reaches about 80% and the grain sizes are a bout 10-50 nm. It is proposed that the fast transformation to c-Si3N4 occur s by rearrangement of nitrogen stacking layers, which initiates partial bre akup of the SiN4 tetrahedra and formation of SiN6 octahedra at high density . Because of the advantages of massive production and the nanometer charact eristics of shock-synthesized c-Si3N4, it is possible to investigate the me chanical properties experimentally and to develop new industrial applicatio ns. (C) 2000 American Institute of Physics. [S0003-6951(00)02025-8].