Characterization of Lanthanum Zirconate Formation at the A‐Site‐Deficient Strontium‐Doped Lanthanum Manganite Cathode/Yttrium‐Stabilized Zirconia Electrolyte Interface of Solid Oxide Fuel Cells

Abstract

Lanthanum zirconate (LZO) formation and growth kinetics between 1273-1673 K at the A-site (La, Sr)-deficient Sr-doped lanthanum manganite (LSM)/yttrium-stabilized zirconia (YSZ) interface were studied using high-resolution transmission electron microscopy-energy-dispersive X-ray spectrometry (HRTEM-EDS). A cross-section TEM sample preparation technique was developed using a dual-beam focused ion beam and an in situ Omniprobe manipulator. The LZO pyrochlore phase was identified at the LSM/YSZ interface by TEM. The LZO is epitaxial with respect to the YSZ phase but not to the LSM phase. EDS results coupled with structural analysis suggest that La diffusion is a critical step in LZO formation. This study shows that LZO formation can occur even for A-sitedeficient LSM with a La composition of 78 mol% (o86 mol%). The activation energy for LZO formation was found to be 16878 KJ/mol. T. Gur-contributing editorThe authors would like to thank the United States Department of Energy for funding under project number DOE project DE-AC05-76RL01830 and Nextech for supplying cathode inks for use in this work.

TEM investigation on zirconate formation and chromium poisoning in LSM/YSZ cathode

“…At the LSM/YSZ interface, EDS mapping and spectra reveal the presence of a new phase, indicative of strontium zirconate (SZO). When the electron probe could be placed accurately on this phase (to exclude other phase superposition in the TEM lamella thickness direction), the measured composition was 20.4 at % Sr, 19.4 at % Zr and the balance of oxygen, which corresponds well to the phase SrZrO 3 .…”

“…When SZO is present, delamination always occurs at the SZO/YSZ interface. Further electron diffraction studies and/or higher resolution TEM would enable to determine whether SZO is in epitaxy with the LSM grain or with YSZ, as observed for LZO [3,6].…”

“…Several phenomena are known to alter the TPB length, such as grain size modification, secondary phase formation, pollutant species deposition or crack occurrence. Reviews of SOFC degradation mechanisms and material interactions can be found in [1][2][3].…”

“…Salvador et al [28] reported TEM observations of Cr 2 O 3 and (CrMn) 3 O 4 nanoparticles filling the cathode pores, the former being the main phase at the LSM/YSZ interface. LZO has been observed by transmission electron microscopy (TEM) [3,6,7] either as nanoparticles or as precipitates grown epitaxially with the YSZ grains at the LSM/YSZ grain boundaries. To our knowledge, no evidence of SZO has been shown by TEM.…”

Co2MnO4 spinel-palladium co-infiltrated La0.7Ca0.3Cr0.5Mn0.5O3− cathodes for intermediate temperature solid oxide fuel cells

“…However, the electrochemical performance of the LSM cathodes decreases dramatically with the reduced temperature due to the negligible oxygen ion conductivity of LSM [19,20]. LSM-based perovskite oxides also react with Y 2 O 3 -ZrO 2 (YSZ), forming lanthanum zirconate resistive phase at temperatures higher than 1200 • C [21,22]. This would limit the potential application of the LSM-based materials for the cathodesupported SOFCs prepared by cost effective fabrication techniques.…”