Shock-induced phase transition of β-Si3N4 to c-Si3N4

Hugoniot curve (shock velocity vs particle velocity and pressure vs density) of beta -Si3N4 has been measured up to 150 GPa by a two-stage light gas gun and an inclined-mirror method. The Hugoniot elastic limit is detected to be about 16 GPa. Above similar to 36 GPa, a phase transition from beta -Si3N4 to c-Si3N4 is discovered. The kinetics is very sluggish. This phase transition does not seem to complete at the highest pressure achieved in this work, but an extrapolation gives a pressure of similar to 180 GPa for the completion. Isentrope of c-Si3N4 has been determined from the Hugoniot data by fitting the Birch-Murnaghan equation of state. The zero-pressure bulk modulus and its first pressure derivative are found to be 300 +/- 10 GPa and 3.0 +/- 0.1, respectively. These values are in agreement with the first-principles calculations, and therefore strongly support that c-Si3N4 is a low compressibility phase.