Vibrational Spectra of Hydrothermally Prepared Hydroxyapatites

Apatites can be used as bioceramic materials for tooth and bone implants. Infrared (4000 to 400 cm^?1) and laser-Raman spectra were obtained for hydrothermally prepared hydroxyapatites with the general formula X₁₀(PO₄)₆(OH)₂ where X= Ca²⁺ Sr²⁺, Ba²⁺, or Pb²⁺ Fundamental vibrational modes were identified and empirical band assignments made. Analysis of the vibrational spectra led to the reassignment of the v₂ mode to a higher wave-number, lower-intensity band (e.g. ～470 cm^?1 for Ca hydroxyapatite). Effects of solid-state interaction were noted in the vibrational spectra and interpreted by factor-group analysis. An "effective" factor group C_6h, which neglects the locations of the OH^? ions, best describes the vibrational spectra of the hydroxyapatites.