Grain Size Effect on Conductivity of LSGM Thin Film Electrolyte for Solid Oxide Fuel Cell

The grain size effect of La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ (LSGM) electrolyte thin film was investigated in order to clarify the mechanism of the change of ion conductivity of thin film. The film was deposited on a LaSrGaO 4 (LSGO) substrate by radio frequency magnetron sputtering and then annealed at 900 o C or 1100 o C to change the grain size in the film. The mean grain size in the films annealed at 900 o C and 1100 o C was 80 nm and 281 nm, respectively. The ion conductivity was measured by electrochemical impedance spectroscopy (EIS). The ion conductivity values of the film of the mean grain size of 80 and 281 nm at 800 o C were σ=1.34×10 -2 and 1.81×10 -2 S/cm, respectively. The activation energy value of both films was 1.08 eV. The grain boundary conductivity obtained by applying the Brick-layer model was nearly two orders of magnitude lower than the bulk conductivity. The activation energy value of the grain boundary conductivity was 1.33 eV. The resistance to transport the ions across the grain boundary should be high. The higher conductivity of the 1100 o C annealed film derives from the decrease of the high resistive grain boundary density.