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.