Shock Synthesis of Cubic Silicon Nitride

The phase transitions of α-Si 3 N 4 and β-Si 3 N 4 have been investigated by shock compression through the recovery technique and Hugoniot measurements. α- and β-Si 3 N 4 are transformed into a cubic spinel structure (c-Si 3 N 4 ). The yield of c-Si 3 N 4 increases with increasing shock pressure and reaches 100% at 63 GPa. The shock-synthesized c-Si 3 N 4 powders are nanocrystals and display a high-temperature metastability up to about 1620 K. c-Si 3 N 4 is one of the hard materials based on the measured equation of state, c-Si 3 N 4 powders have been characterized by electron microscopy and 29 Si magic angle spinning NMR spectroscopy. The purification and separation method has been developed to obtain pure c-Si 3 N 4 powders.