Change in Surface Composition of La0.9Sr0.1Ga1-XMgxO3- d Investigated with Low Energy Ion Scattering Analysis

Abstract

In oxide based energy conversion devices, e.g. fuel and electrolyser (SOFCS and SOECS), predominantly materials crystallizing in the perovskites structure are employed as both, electrodes and electrolyte. Being exposed to realistic operation conditions, however, both components suffer from various degradation phenomena. Here surface segregation and interface diffusion are of pivotal practical importance, as both phenomena are known to deteriorate device performance. Up to now, surface segregation was mainly studied on perovskite oxide cathode and it was found that A site is always segregated surface, in particular, alkaline earth cation is easily segregated on the surface. In this study, change in surface composition by alkaline earth element in one of the most promising electrolyte material - La0.9Sr0.1Ga1-xMgxO3- δ (LSGM)- were investigated. Samples of different Mg content x were subjected to anneals at high-(> 1000 K), intermediate ( 1000< T/K < 650) and low temperatures (>650 K). The composition of the very outermost surface layer was subsequently analyzed by means of low energy ion scattering (LEIS). In analyzing the results, the focus was set on differences in A and B side surface coverage and changes with temperature, time and composition. Moreover, links between Ni diffusion at interfaces observed in devices employing LSGM and the here described surface segregation phenomena in the same material were established. It was found that Mg2+ in B site was first segregated but after annealed for longer period, Sr2+ in A site was segregated and so the surface segregated cation was changed depending on the annealing period. Decreasing Mg content, Mg segregation is not observed and this is related with the Ni diffusion in LSGM film prepared by dip coating method.