Infrared and Raman microspectrometry study of fluor-fluor-hydroxy and hydroxy-apatite powders

Visible Raman and infrared microspectrometry studies performed on fluorapatite and hydroxyapatite powders have shown similar results. Small modifications of the nu2 and nu4 PO(3-)4 tetrahedra bending modes are observed. A small frequency shift of the nu1 mode and modifications on the nu3 mode region accompanied with a simplification of the hydroxyapatite and fluorapatite respective spectra from seven to four bands were observed. A broad and weak band which could be attributed to the Ca-F bond is detected at 311 cm(-1) on the Raman fluorapatite spectra. The phosphate vibration modes are little disturbed by fluoride substitution. This could indicate that phosphate groups interact strongly between themselves and weakly with substituted atoms (i.e. hydroxyle and fluoride atoms). Whatever crystallographic model is considered, the number of bands observed is always lower than the number of calculated ones, even for hydroxyapatite, whose symmetry is lower than that of fluorapatite.