The Variation of Lattice Parameters with Composition in Solid Solutions of Hydroxylapatite and Fluorapatite

Solid solutions of hydroxylapatite (OHA) and fluorapatite (FA) were prepared from CaCO3, CaHPO4.2H2O and CaF2 by solid‐state reaction at 1000°C in a stream of nitrogen which was saturated with water vapor at 0°C. Determinations of the lattice parameters were carried out by step scanning of certain X‐ray reflections. It was found that the value of the lattice parameter a varied linearly with the fluoride content. No segregation into two apatite phases was observed, when solid solutions were heated at 250°C for 300 hours. The consequences of this study for the behaviour of these solid solutions in contact with aqueous solutions are discussed. Thereby, attention is focussed on the caries‐preventive action of fluoride ions.