Shock wave induced phase transitions from the trigonal phase to the coexisting amorphous and orthorhombic phases in α-FePO[sub 4

Abstract

The shock induced response of berlinite form of α-FePO4, which has been studied recently under static pressure, has been investigated in order to examine the effect of shear and high temperature on the process of amorphization in this material. The samples were shock loaded up to 8.5 GPa in a gas gun and after recovery were analyzed using x-ray diffraction (XRD) technique. The sample retrieved from 5.2 GPa revealed an irreversible phase transformation of some of the material to an amorphous and a crystalline orthorhombic structure (space group Cmcm), which are co-existing. The XRD pattern of the 8.5 GPa sample on the other hand displayed the presence of only the orthorhombic phase along with the ambient structure. The absence of the the amorphous phase is attributed to the reverse transformation due to the high residual temperature in the 8.5 GPa sample. Since the Cmcm phase is equilibrium high pressure phase of such materials, the results could be interpreted on the three level free energy diagram. The comparison of these results with those reported under static pressure is presented.