Doped silicated rare earth apatites with formula La9.33−xCax(SiO4)6O2−x/2 (0 ≤ x ≤ 1) were prepared by solid state reaction at high temperature in order to determine the influence of anionic vacancies on the electrical properties of the material. The incorporation of calcium in the structure was checked by characterizations of the powders (X-ray diffraction, helium pycnometry). The cell parameters of the hexagonal apatite were refined. Samples were sintered at 1550C. Electrical properties of each composition were studied between 280 and 620C by the complex impedance method. The evolution of the bulk conductivity and of the activation energy with the substituting ratio gives information on the conductivity mechanism in these materials. An improvement of ionic conductivity about one order of magnitude was observed for low calcium substitution ratios.

Influence of Anionic Vacancies on the Ionic Conductivity of Silicated Rare Earth Apatites. P.J.Panteix, E.Béchade, I.Julien, P.Abélard, D.Bernache-Assollant: Materials Research Bulletin, 2008, 43[5], 1223-31