Calculation of the Raman line broadening on carbonation in synthetic hydroxyapatite

The position and broadening of the Raman band associated with the phosphate symmetric stretching vibration in hydroxyapatite are simulated using a simple inter- and intra-ionic potential. The results are compared with experimental values. This comparison was made as a function of the incorporation of carbonate ions in the lattice for a number of substitution models. The line width of the phosphate symmetric stretching vibration is shown both theoretically and experimentally to be dependent on the carbonate content. Good agreement between calculations and experiment is obtained. The results of the calculations offer some support to the suggestions in the literature that the dielectric constant has to be considered as a function of the distance in the lattice, increasing beyond the first environmental layer.