Hugoniot of beta-SiAlON and high-pressure phase transitions

Hugoniot equation-of-state data of shock compressed β‐Si4Al2O2N6 have been determined to a pressure of 120 GPa. The relationship between shock velocity (Us) and particle velocity (Up) is expressed by a linear equation Us(km∕s)=5.62+0.96Up(km∕s) above a pressure of ∼40GPa beyond the Hugoniot elastic limit (15–16 GPa). A phase transition to spinel is observed at the onset pressure of 32 GPa. According to the systematics of high-pressure phase transitions of spinels that indicate a phase transition to CaTi2O4-type phases at high pressures, β‐Si4Al2O2N6 may also be transformed into a CaTi2O4-type phase with further increasing pressure. The previous recovery experiments on β-SiAlON indicated the formation of spinel and amorphous phases at shock pressures of 41–63 GPa. A comparison of the Hugoniot data and recovered samples suggests that the high-pressure CaTi2O4-type phase is not quenchable and quenched as an amorphous phase although a large hysteresis is detected in the release path.