Synthesis, Rietveld refinements and electrical conductivity of news fluorobritholite based on lead Ca7-xPbxLa3(PO4)3(SiO4)3F2 (0 ≤ x ≤ 2)

Abstract

Fluorobritholites of general formula Ca7–xPbxLa3(PO4)3(SiO4)3F2, (0 ≤ x ≤ 2) were prepared by thermal method. The obtained solid solutions were characterized by X-Ray diffraction, infrared spectroscopy and chemical analysis. The structural refinement carried out via the Rietveld method provides evidence that La3+ and Pb2+ substituting Ca2+ ions are located into the two cationic sites with a strong preference for metal M(2) sites. A progressive shift of the F− ion toward the center of the triangles formed by the site M(2) metals has been observed when the lead content increased. The electrical conductivity of the fluorobritholite materials depends on the applied frequency (100 Hz–10 MHz) by means of the complex impedance spectroscopy. The effect of Pb and La-substitution on the conductivity properties of the studied fluorobritholites is correlated with Pb content. The carriers that govern the conductivity are: the nature of the welcome sites and the dimension of the tunnels.