Microstructure and electrical conductivity of alkaline elements doped apatite-type La10Si6O27 electrolytes

•Lanthanum silicates are doped on La3+ site with alkali elements (Li+, Na+ or K+).•Property of the doped samples sintered at different temperatures is investigated.•The sinterability of apatite electrolytes is improved by the alkali elements doping.•La9.95K0.05Si6O26.95 exhibits the highest conductivity of 1.12×10−2 S cm−1 at 800 °C.

Alkali elements doped lanthanum oxyapatites La9.95A0.05Si6O26.95 (A=Li+, Na+, K+) are synthesized successfully by the solid state reaction. The structure, morphology and composition of La9.95A0.05Si6O26.95 electrolytes are characterized by XRD, SEM and EDS, respectively. The electrical properties of La9.95A0.05Si6O26.95 ceramics are investigated by electrochemical impedance spectroscopy (EIS). The results show that all the La9.95A0.05Si6O27−δ electrolytes consist of a single hexagonal apatite structure without impurity. The sinterability of apatite electrolytes is improved by the alkali elements doping and the densification sintering of the electrolytes can be achieved at 1550 °C. Among the alkali element doped samples, La9.95K0.05Si6O26.95 exhibits the lowest activation energy for the electrical conduction and the highest conductivity of 1.12×10−2 S cm−1 at 800 °C.