Extraordinary fast oxide ion conductivity in La1.61GeO5−δ thin film consisting of nano-size grain

Thin films of La1.61GeO5−δ, a new oxide ionic conductor, were fabricated on dense polycrystalline Al2O3 substrates by a pulsed laser deposition (PLD) method and the effect of the film thickness on the oxide ionic conductivity was investigated on the nanoscale. The deposition parameters were optimized to obtain La1.61GeO5−δ thin films with stoichiometric composition. Annealing was found necessary to get crystalline La1.61GeO5−δ thin films. It was also found that the annealed La1.61GeO5−δ film exhibited extraordinarily high oxide ionic conductivity. Due to the nano-size effects, the oxide ion conductivity of La1.61GeO5−δ thin films increased with the decreasing thickness as compared to that in bulk La1.61GeO5−δ. In particular, the improvement in conductivity of the film at low temperature was significant .The electrical conductivity of the La1.61GeO5−δ film with a thickness of 373 nm is as high as 0.05 S cm− 1 (log(σ/S cm− 1) = − 1.3) at 573 K.