A series of apatite-type lanthanum silicates La9.33+xSi6O26+1.5x (LSO) are synthesized via a sol-gel process. Differential thermal analysis, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and Raman measurements are performed to examine the phase present and morphology of LSO. It revealed that LSOs with 9.33 + x <= 10 calcined at 900 degrees C are identified as pure oxyapatite phase with an average grain size of 30 nm. LSOs with 9.33 + x <= 9.5 sintered at 1600 degrees C are also identified as single apatite phase. Based on 2 and 4-probe AC impedance spectroscopy measurements, the dependence of calcination temperature and composition on the electrical conductivity of LSOs are evaluated. Samples with composition of La9.5Si6O26.25 and La9.33Si6O26 function as purely ionic conductors, exhibiting high conductivities of 1.6 x 10(-2)S cm(-1) and 1.3 x 10(-2) Scm(-1) at 800 degrees C. (c) 2013 Elsevier B.V. All rights reserved.