Synthesis and electrical conductivity of La10Si5.5B0.5O27 + δ (B = In, Si, Sn, Nb) ceramics

► La10Si5.5B0.5O27 + δ ceramics were prepared by sintering at 1923 K. ► La10Si5.5B0.5O27 + δ ceramics have apatite structure. ► Lanthanum silicates doped with In or Nb cations exhibit higher total conductivity. ► The highest conductivity at 1073 K is 1.75 × 10− 2 S·cm− 1 for La10Si5.5In0.5O26.75.