Pressure induced amorphization in calcium phosphates

Polycrystalline hydroxylapatite (HA), hydrated tricalcium phosphate (HTCP), tricalcium phosphate ( TCP), dicalcium phosphate dihydrate (DCPD) and dicalcium phosphate anhydrous (DCPA) were subjected to various pressures upto 10 GPa and the retrieved materials were examined by XRD and FTIR. These compounds showed amorphization at pressures upto 10 GPa, the pressure being lowest for HTCP and DCPA. At intermediate pressures, the amorphous phase obtained was anisotropic. Significant changes in the infrared spectra were observed in all materials except DCPA. These changes are due to the lowering of site symmetry on amorphization.