FT-Raman and high-pressure infrared spectroscopic studies of dicalcium phosphate dihydrate (CaHPO_4 centre dot 2H_2O) and anhydrous dicalcium phosphate (CaHPO_4)

摘要

The FT-Raman spectra and the pressure dependence of the infrared spectra of the hydrated and anhydrous forms of dicalcium phosphate, CaHPO_4 centre dot 2H_2O and CaHPO_4, have been studied. The hydrated salt exhibits a phase transition at 21 kbar (1.0 kbar=0.1 Gpa) but no high pressure transition was observed for anhydrous dicalcium phosphate. The O-H stretching frequencies of the water molecules in CaHPO_4 centre dot 2H_2O all showed negative pressure dependences and correlate with the O...O distances. The PO-H stretch increased with increasing pressure, indicating a strong hydrogen bond. The frequencies associated with the phosphate ion showed a normal pressure dependence.