Shock Synthesis of Cubic Silicon Nitride

The phase transitions of α-Si₃N₄ and β-Si₃N₄ have been investigated by shock compression through the recovery technique and Hugoniot measurements. α- and β-Si₃N₄ are transformed into a cubic spinel structure ( c -Si₃N₄). The yield of c -Si₃N₄ increases with increasing shock pressure and reaches 100% at 63 GPa. The shock-synthesized c -Si₃N₄ powders are nanocrystals and display a high-temperature metastability up to about 1620 K. c -Si₃N₄ is one of the hard materials based on the measured equation of state. c -Si₃N₄ powders have been characterized by electron microscopy and ²⁹Si magic angle spinning NMR spectroscopy. The purification and separation method has been developed to obtain pure c -Si₃N₄ powders.