Hugoniot of beta-SiAlON and high-pressure phase transitions

Hugoniot equation-of-state data of shock compressed beta-Si4Al2O2N6 have been determined to a pressure of 120 GPa. The relationship between shock velocity (U-s) and particle velocity (U-p) is expressed by a linear equation U-s (km/s) = 5.62+ 0.96U(p) (km/s) above a pressure of similar to 40 GPa 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, beta-Si4Al2O2N6 may also be transformed into a CaTi2O4-type phase with further increasing pressure. The previous recovery experiments on beta-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. (c) 2006 American Institute of Physics.