**4. Conclusion**

Strontium fluorbritholites Sr8La2�xNdx(PO4)4(SiO4)2F2 with (0 ≤ x ≤ 2) were successfully prepared by reaction in the solid state. Characterization by several techniques revealed that all the powders were composed of a single apatite phase. The lattice parameters *a* and *c* were inversely proportional to Nd content. The La-Nd substitution was totally coherent with the ionic size of lanthanum and neodymium ions. The chemical analysis showed that for all the compositions the ratio SrþLaþNd <sup>P</sup>þSi was close to the stoichiometric value (1.667) indicating the stoichiometry of the powders. The Infrared absorption apectroscopy study confirmed the presence of the absorption bands relative to PO4 and SiO4 groups. The 31P NMR (MAS) showed the presence of a unique isotropic signal confirming the existence of a single crystallographic site for the phosphorus nucleus. The materials' ionic conductivity measured via impedance spectroscopy was found to be heating-dependent. The maximum of 1.73 � <sup>10</sup>�<sup>6</sup> S cm�<sup>1</sup> is obtained with higher Nd level and at a temperature of around 1052 K.
