Thermal stability of cadmium–calcium hydroxyapatite solid solutions

Abstract

A continuous series of solid solutions of cadmium and calcium hydroxyapatite has been prepared from aqueous solution and characterized by X-ray diffraction and i.r. spectroscopic analyses. The lattice dimensions and the i.r. frequencies of the solid solutions vary linearly with the atom % of the cadmium. Upon heat treatment these solid solutions are converted into the β and α forms of cadmium-substituted tricalcium phosphate. Cadmium promotes these thermal conversions, having a destabilizing effect on the apatite structure. This effect cannot be explained by the small differences in the ionic radius of cadmium and calcium ions, but instead to differences in the nature of the cation–oxygen interactions.