Synthesis and characterization of strontium–lanthanum apatites

Two series of strontium–lanthanum apatites, Sr10−xLax(PO4)6−x(SiO4)xF2 and Sr10−xLax(PO4)6−x(SiO4)xO with 0 ≤ x ≤ 6, were synthesized by solid state reaction in the temperature range of 1200–1400 °C. The obtained materials were characterized by powder X-ray diffraction, infrared absorption spectroscopy and solid 31P Nuclear Magnetic Resonance. Pure solid solutions were obtained within a limited range of unsubstituted phosphate and silicate apatites. A variation of the lattice parameters was observed, with an increase of a and a decrease of c parameters, related to the radius of the corresponding substituted ions.