Morpho-structural and electrical characterization of Bi-doped apatite-type lanthanum silicates prepared by gel-combustion

Abstract

La10−xBix(SiO4)6O3 ceramics (x = 0; 0.1; 0.15; 0.2; 0.3) were obtained from precursors prepared by gel combustion using l-aspartic acid as fuel. This study presents the effect of Bi3+ doping level and sintering temperature on the morpho-structural and electrical properties of apatites. Processes involved in the apatite formation same as crystallization temperature were examined through TGA. The XRD patterns have showed that all samples adopt the apatite structure and crystallize in the hexagonal space group P-3(147). Samples crystallite size varies between ~ 58 and ~ 118 nm depending on the Bi3+ doping level and the sintering temperature. In order to explain the conduction in apatite, the preferential position of Bi3+ in lattice and the occupancy factors of O5, O6 were calculated by Rietveld refinement. ICP-OES and XPS measurements give the bismuth amount accommodated in apatite lattice and its oxidation states. The morphology, homogeneity and compactness of the ceramics at different Bi doping level were examined through SEM. The relative density of the material is enhanced by the sintering temperature up to 1500 °C, reaching 91.63% for sample doped with 1.5% Bi. Through EIS investigations, the conductivities at 500 °C, for sample doped with 1.5% Bi, are: 9.22 × 10−5 Scm−1 (sintered at 1400 °C) and 1.02 × 10−3 Scm−1 (sintered at 1500 °C), respectively, values which are higher than that of un-doped apatite (6.46 × 10−5 Scm−1).