Effect of the valence states of titanium on the lattice structure and ionic conductivity of Li0.33La0.55TiO3 solid electrolyte

Li0.33La0.55TiO3 solid electrolytes with a pure phase were synthesized by the citric acid-supported sol-gel method and then sintered under controlled redox atmospheres of air, argon and hydrogen. Although of similar morphology and relative density, Li0.33La0.55TiO3 samples sintered under reduction atmosphere such as argon and hydrogen exhibited a tetragonal structure with lattice distortion. The distortion and volume expansion of the crystal lattice was identified as originating from the transformation of the Ti valence state, and this was more clearly observed under sintering of the hydrogen atmosphere. The qualitative analysis of the Ti valence state using an X-ray Photoelectron Spectroscopy experiment was performed and indicated that the largest amount of Ti3+(18.6%) was formed in the Li0.33La0.55TiO3 samples sintered under hydrogen atmosphere. The relationship between the lattice distortion and the lithium ion conductivity of the Li0.33La0.55TiO3 sintered under different atmospheres is also discussed on the basis of the lattice distortion.