Structure and ionic conductivity of cerium doped La9.33-xCexSi6O26 apatite-type lanthanum silicates

Abstract

In this work, the effect of cerium doping on the structure and ionic conductivity of the apatite-type lanthanum silicates is presented. Ceramic samples with nominal composition of La9.33-xCexSi6O26 (x = 0, 0.1, and 0.2) are synthesized via a solid-state reaction process. They are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and complex impedance measurements. The study shows that the samples, having small amount of secondary phases of La2SiO5 and La2Si2O7, crystallize in the hexagonal apatite type structure with P63/m space group. The doping increases first the cell parameters for x = 0.1 before decreasing for x = 0.2. It also increases the grain size of the samples and reduces their porosity. The complex impedance measurements have been carried out in the temperature range 625–769 °C. The results are treated by separating the grain from the grain boundaries components and show that the ionic conductivity is remarkably improved by this kind of doping.