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].