Inelastic neutron scattering studies of synthetic calcium phosphates

Infrared and Raman spectra have been used extensively for the characterisation of the mineral component of mineralised tissues, especially bone and teeth. Often the vibrational modes of hydroxy groups and hydrogen phosphate are masked in the presence of substituent anions such as carbonate. The inelastic neutron scattering (INS) spectra are dominated by the vibrations of groups with hydrogen or with hydrogen riding on groups. Two sets of bands have been assigned to the hydroxy librations related to the hexagonal and monoclinic polymorphs of hydroxyapatite. Of the phosphate bands in brushite only the HPO42- bands are seen in the INS spectrum. These INS studies of synthetic hydroxyapatites and brushite present new opportunities for studying aspects of biominerals not accessible by standard vibrational techniques.