Lithium ion conductivity of oriented Li0.33La0.56TiO3 solid electrolyte films prepared by a sol–gel process

• Sol–gel derived Li3xLa2/3 − xTiO3 thin films with a-axis orientation were synthesized.
• The bulk conductivity was 4.42 × 10− 5 S/cm for a 411-nm-thick film.
• The conductivity was almost 10-times-higher than that previously reported for sol–gel-derived films.

Lithium lanthanum titanates (Li3xLa2/3 − xTiO3, LLTOs) having a-axis orientations were synthesized via a simple sol–gel route on SrTiO3 and Nb-doped SrTiO3 substrates. The lithium ion conduction behaviors of the LLTO films were determined. Annealing the films above 1200 °C yielded strong a-axis growth orientation, while heating samples above 1300 °C led to the reduction of the Li transference number, TLi, which was attributed to Li evaporation. The optimized annealing temperature was 1200 °C, where both the bulk conductivity, σdc, and the TLi exhibited their maxima. The bulk conductivity was 4.42 × 10− 5 S/cm for a 411-nm-thick film, which was almost 10-times-higher than that previously reported for sol–gel-derived films. A key reason for the enhancement in conductivity is the expanded bottleneck of the LLTO lattice because of a tensile stress induced by the substrate. Optimization of the annealing temperature and the film thickness further improved the conductivity.