Extraordinary fast oxide ion conductivity in La_1.61GeO_5-δ thin film consisting of nano-size grain

Thin films of La_1.61GeO_5-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 La_1.61GeO_5-δ thin films with stoichiometric composition. Annealing was found necessary to get crystalline La_1.61GeO_5-δ thin films. It was also found that the annealed La_1.61GeO_5-δ film exhibited extraordinarily high oxide ionic conductivity. Due to the nano-size effects, the oxide ion conductivity of La_1.61GeO_5-δ thin films increased with the decreasing thickness as compared to that in bulk La_1.61GeO_5-δ. In particular, the improvement in conductivity of the film at low temperature was significant .The electrical conductivity of the La_1.61GeO_5-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.