Stabilization of Calcium Oxyapatites with Lanthanum(III)-Created Anionic Vacancies

Two series of samples of the system Ca 10 - x La x (PO 4 ) 6 (OH) y (0 ≤ x ≤ 2), have been synthesized by solid-state reaction at high temperature. In this composition range the apatite structure is maintained. Cationic distribution was analyzed by Rietveld refinement of the XRD data, showing a preferential substitution of La(III) ions in the Ca(2) position. The introduction of the trivalent ion provokes the transformation of OH - to O 2 - ions. Stable oxy- or oxyhydroxyapatites with numerous anionic vacancies have been synthesized as a function of the lanthanum content or the synthesis conditions.