Microstructural Characterization of La-Cr-O Thin Film Deposited by RF Magnetron Sputtering on the Stainless Steel Interconnect Materials for SOFC Application

Abstract

LaCrO3 based perovskites thin films are a prospective material as a protective coating against oxidation and corrosion of metallic interconnect for SOFCs. However, for RF magnetron sputtered LaCrO3 films, the microstructural development of amorphous films during annealing has not been reported, despite the importance of the crystallization processes as one of the factors determining the final properties of the film. SEM and TEM were employed to study the microstructure of the La-Cr-O thin films deposited by RF magnetron sputtering on the stainless steel substrate. The “as-deposited” La-Cr-O thin film was found to be X-ray amorphous with no visible spots in electron diffraction pattern, but after annealing in air, the film transforms first to LaCrO4 monazite type monoclinic phase at 495–530°C and further to the orthorhombic LaCrO3 perovskite at 800°C. In certain cases the second transition to the LaCrO3 perovskite occurred at 700°C. Formation of the porous self-organized LaCrO3 structure was studied by SEM and in-situ high temperature TEM. The effect of environment (air, vacuum, hydrogen) on the microstructural evolution of La-Cr-O thin films during annealing is reported.