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edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 2 24 two such particles contrasted against the surrounding LSM and YSZ grains. To characterize the nanoparticles and to obtain infor- mation associated with the formation of these particles, chemical and electronic structure analyses are performed. An LSM grain, which is in contact with two YSZ grains adjacent to the electrolyte interface, is selected to carry out this study. This selection ensures the combination of a more accurate EDS chemical analysis by minimiz- ing intense signals from the bulk electrolyte materials and with a suitable grain size required for resolvable EFI mapping. The EFI mapping results are presented in Fig. 3, including the zero-loss bright-field (BF) image and a series of elemental maps for Zr, La, and Mn individu- ally. The phase map is also included to provide a better illustration of the phase distribution. Several Zr-rich areas with depleted La and Mn are observed inside the LSM grain near the LSM/YSZ interfaces. This presence of Zr inside LSM grain suggests Zr ion could have diffused from YSZ grain into LSM grain during operation. The size of these Zr-rich areas is measured to be around 20 to 35 nm, agreeing with those observed in Fig. 2. This indi- cates these nanoparticles in Fig. 2 may also be Zr-rich particles. (This was further confirmed with EFI mapping. Results not shown here.) Additionally, a large blue area is observed between two YSZ grains. Based on the EDS results, Mn is the primary cation detected inside this blue area and therefore, is probably aMn-oxide phase. The EDS results suggest that excessMn ions have diffused fromLSM grain and precipitated out as Mn-rich regions. Detailed chemical information across these Zr-rich particles and the surrounding LSM grain is obtained employing the STEM-EDS technique. The results are given in Fig. 4, including the STEM bright-field image depicting the line scan location and the concentration profile. The EFI phase map from Fig. 3 (inset) illustrates the line scan position and direction with respect to the LSMandZr-rich grains. Several features are to be noticed here: firstly, a signifi cant amount of Zr is detected across the en tire length of the line scan, indicating that th e Zr ions diffuse into the LSM grain. Secondly, several areas are revealed to contain higher Zr concentrations than Mn and La, suggesting Zr replacing La andMn in the formation of Zr-rich particles inside LSM. In addition to chemical analysis, the electronic structure is also studied with STEM-EELS. Figure 5a shows the background subtracted STEM-EELS spectra over a range of O- K and Mn- L 2,3 edges acquired from the same area as the STEM-EDS in Fig. 4. TheO- K edge is selected for electronic structure anal- ysis because substantial differences regard- ing the edge shape and onset position for the O- K edge between LSM and YSZ phases iswell documented. [16,17] TheMn- L 2,3 edge can be used to determine the valence state of Mn. With this complementary valence state information, it can assist in more precisely resolving theMndiffusionmechanismacross LSMand YSZ asMn primarily dissolves in YSZ as Mn +2 , while it exists mostly as Mn +3 in LSM. The STEM-EELS acquisition starts from the bulk LSMphase. It is noted that the repre- Fig. 4 The STEM bright-field image with the phasemap (inset) illustrating the areawhere the line scan is acquired across the LSMgrain adjacent to the LSM/YSZ interface, and the corresponding concentration profile plot. The step size is ~3.5 nm/step, (air flow cell). Fig. 3 A series of energy-filtered imaging images, including (a) the zero-loss image taken across the cathode/electrolyte interface; and the (b) Zr, (c) La, and (d) Mn elemental maps. (e) A phase map obtained by superimposing Zr, Mn, and La maps, (air flow cell).