Sol-gel synthesis and ionic conductivity of oxyapatite-type La9.33+xSi6O26+1.5x

► Apatite-type La9.33+xSi6O26+1.5x are synthesized via a sol-gel process. ► Powders with 9.33 + x ≤ 10 calcined at 900 °C are pure oxyapatite phase with grain size of 30 nm ► Samples sintered at temperature of 1600 °C have high relative density of more than 95%. ► Sintered samples with 9.33 + x ≤ 9.5 are apatite phase. ► TheLa9.5Si6O26.25 exhibits superior ionic conductivity of 1.6 × 10−2 Scm−1 at 800 °C.