Solid-state NMR and Raman spectroscopic investigation of fluoride-substituted apatites obtained in various thermal conditions

Abstract

Fluoride-substituted apatites were synthesized by the standard sol-gel method and then calcined at three different temperatures: 800 °C, 1000 °C, and 1200 °C. Using a similar method, hy-droxyapatite was synthesized and used as a reference material. The obtained powders were charac-terized by physicochemical methods: powder X-ray diffractometry, Raman spectroscopy, transmission electron microscopy, and solid-state nuclear magnetic resonance. All these methods allowed to identify additional α-TCP phase (tricalcium phosphate) in the HAP samples heated at 1000 °C and 1200 °C while fluoridated apatites turned out to be thermally stable. Moreover, Raman spectroscopy and NMR allowed to establish that the powders substituted with fluoride ions are not pure fluorap-atite and contain OH-groups in the crystal structure. All the obtained materials had crystals with a shape similar to that of biological apatite.