Transmission electron microscopy (TEM) with EDS confirms the existence of Fe-Ni-Ru alloy@FeOx core-shell nanoparticles on the reduced SFMNR perovskite oxide. Nanoparticles are approximately 100 nm in diameter, dispersed and well-connected on the surface of the host oxide (Figures ). The EDS analyzes show that the nanoparticles are composed of Fe-Ni-Ru alloy core in a ratio of approximately 8:1:1 (area 1 in Figure ) along with an FeO shell in a Fe to O ratio of about 1:1 (area 2 in Figure and). The highresolution TEM image in Figure shows that the nanoparticles grow on the host perovskite oxide, where a plane distance of 0.28 nm is indexed to (110). The thickness of the FeOx shell is about 3 nm, where the observed plane distance of 0.22 nm agrees with that of the (200) plane. All the TEM and in-situ XRD results consistently support the formation of Fe-Ni-Ru alloy@FeOx core-shell nanoparticles on the surface of Sr2Fe1.5Mo0.4Ni0.05Ru0.05O6-δ oxide after the reduction treatment.