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edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 2 28 value reported in Wiik et al. [18] In the Zr-rich phase, a com- pletely different diffractionpattern is obtainedas shown in Fig. 6c, suggesting a different atomic structure from the bulk LSMgrain. Despite a non-perfectly parallel diffraction pattern along the zone axis, this Zr-rich phase exhibits a much shorter distance between two neighboring diffrac- tion spots in comparison with the LSM phase, indicating a larger lattice parameter. (The lattice parameter of LZO is 10.8Å, which ismuch larger than that of LSM.) [19] Although more study and investigation are required in resolving detailed structural information concerning this Zr-rich phase, the current chemical and structural analysis clearly demonstrates that Zr-rich phases with different structure form inside the LSM phase. OXYGEN-TESTED CELL The TEM analyses of the cathode/electrolyte interface in the oxygen-tested cell are presented in Fig. 7, including the TEMzero-loss image, and the corresponding EFI phase map. An agglomeration of LSM grains is observed to be in close contact with the YSZ electrolyte. In addition to the LSM (green) and YSZ (red), several isolated blue areas, approximately 30 to 100 nm in size, are also seen to be embedded along the LSM/YSZ interfaces. These blue areas are enriched with Mn and depleted of Zr and La. No formation of LZO is found. A location with a Mn-rich grain sandwiched between YSZ and LSM phases is selected for investigation regard- ing the atomic diffusion mechanism associated with the Mn-rich grain formation using the STEM-EDS technique. Figure 8 illustrates a STEM bright-field image and the line scan location together with its concentration profile. The arrows I 1 and I 2 indicate the interface of the YSZ/Mn-rich grain and the Mn-rich grain/LSM, respectively. The EFI phase map from Fig. 7 is inset in Fig. 8 to indicate the relative line scan positionwith respect to each phase. The results show that the Mn-rich grain primarily contains Mn cationwith only aminor concentration of other elements, indicating aMn-oxide phase. It is also noted that no Zr or Y content is observed inside the LSMphase. Similarly, no La and Sr are observed to be present inside the YSZ phase. These findings suggest that no significant cation diffu- sion occurred between LSM and YSZ under the current testing condition of pure oxygen environment. STEM-EELS analysis was also carried out in the same location. The result is given in Fig. 9, illustrating the background-subtracted EELS spectra. I 1 and I 2 are also denoted. Again, the O- K edge and Mn- L 2,3 edge are selected for the electronic structure analysis. Distinctive Mn- L 2,3 edges with high intensity are observed for both the LSM and Mn-rich grains. This indicates that both phases contain relatively high Mn concentrations, in agreement with the EDS results. In view of the O- K edge, the representative fingerprint edges (shown in Fig. 5b) reported in the literature are observed for both YSZ and LSM phase. [16,17] However, a completely different O- K edge profile is observed for the Mn-rich phase, indicating that the O atoms exhibit a different electronic structure. This finding further verifies that this Mn-rich phase is indeed a third phase formed along the LSM/YSZ interface. Another feature to be noted is that a small Mn- L 2,3 edge (arrowed) is visible inside the YSZ phase adjacent to the YSZ/Mn-rich grain interface (I 1 ), confirming a low level of Mn diffusing into the YSZgrain. This is consistentwith theSTEM-EDS results in Fig. 8. Fig. 8 The STEM-EDS result acquired across YSZ/Mn-rich/LSM phases, including the STEM bright-field image (left) and the resulting concentration profile plot of each element (right). The step size is ~5.6 nm/step, (oxygen flow cell). Fig. 7 (a) The TEM zero-loss image taken across the cathode/electrolyte interface in the cell tested in oxygen and (b) the corresponding EFI phase map, (oxygen flow cell). OXYGEN PARTIAL PRESSURE EFFECT ON EARLY LSM-YSZ SURFACE INTERACTIONS (continued from page 25)