Effect of calcium doping on La4(Ti2O8)O2 structure and conductivity

La4-xCaxTi2O10-δ (x = 0; 0.1; 0.2) powders were synthesized by a modified Pechini method. Thermal treatement of the powders under reducing atmosphere (2% H2 in Ar) and their sintering in air led to changes in unit cell parameters and unit cell volume. A decrease in long range ordering and symmetry with the increase in dopant content after sintering was evidenced by Raman spectroscopy, in agreement with the results of conductivity measurement performed under air. The ionic conductivity increases with two orders of magnitude after doping with calcium. The activation energy of conduction for doped samples decreases compared to the undoped sample, indicating a change in the conduction mechanism. Doped samples exhibit an increase in conductivity and activation energy of conduction after exposure to highly reducing atmosphere.