Influence of Substrate on Conductivity of Sr and Mg Doped Lanthanum Gallate Thin Film Electrolyte for Solid Oxide Fuel Cell

In order to reveal the influence of substrate on the conductivity change of La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-δ (LSGM) thin film from the bulk, we prepared LSGM thin films on the sapphire and the quartz substrates by radio frequency magnetron sputtering, and evaluated the crystallinity, the microstructure, and the conductivity. The lattice constant of 0.6 μm thick film was different between the substrates. Compared with the bulk, the lattice constant of the thin film on the sapphire substrate was decreased 1.3%, and that on the quartz substrate was increased 0.7%. The grains in the thin film on the quartz substrate were approximately 0.2 μm in size, and those on the sapphire substrate were approximately 0.1 μm in size. The conductivity was measured at 710 °C by electrochemical impedance spectroscopy. The conductivity of the thin film on the quartz substrate was σ = 2.2 × 10 -3 Scm -1 and that on the sapphire substrate was 9.0 × 10 -4 Scm -1 . The reason why the thin film on the quartz substrate had higher ion conductivity than that on the sapphire substrate can be attributed to the higher density of the grain boundaries which govern the total resistivity of the film on the quartz substrate than that on the sapphire substrate.