Apatite Formation: Why It May Not Work as Planned, and How to Conclusively Identify Apatite Compounds

Table 3

FTIR characteristic bands (PO₄³⁻ and OH⁻) for stoichiometric HA.

Hydroxyapatite (HA) Ca10(PO4)6(OH)2
Band position (cm^−1) (±2 cm^−1)	Relative intensity	Attributions
PO4^3− groups (apatitic)
474 (isolated)	very weak	ν 2(PO4): OPO bending
562 and 575 (merged together)	moderate	ν 4(PO4): OPO bending
603 (isolated)	moderate	ν 4(PO4): OPO bending
962 (isolated)	weak	𝜈1(PO4): PO stretching
1048, 1090 (both isolated)	intense	ν 3(PO4): PO stretching
OH^− groups (apatitic)
632 (shouldered to ν 4(PO4))	moderate/weak	𝜈𝐿(OH): OH libration
3572 (shouldered to water O–H)	moderate/weak	𝜈𝑠(OH): OH stretching