In a solid oxide fuel cell (SOFC) whose cathode is composed of Sr-doped LaMnO3 (La1−xSrxMnO3, LSM) and Y2O3-stabilized ZrO2, the reduction of oxygen on the surfaces of the LSM is critical to the performance of the SOFC. As a first step toward identifying the key LSM surfaces that are present in the SOFC and a better understanding of the reduction process, the energetics of cubic LaMnO3 surfaces are appropriate to examine (cubic LaMnO3, c-LM). Previously, several theoretical studies of the c-LM low-index surfaces, (001), (011), and (111), were performed. In this work, the c-LM high-index surfaces are examined for the first time. The first six c-LM high-index surfaces, (210), (211), (221), (310), (311), and (320), are examined. The surface energies of the surfaces are computed as a function of surface model thickness. Both unrelaxed and relaxed surface energies are obtained using unrelaxed and relaxed surface models, respectively. The (210) surface of c-LM is shown to be nearly as stable as (001), the most stable c-LM low-index surface. Also, the (320), (211), and (221) surfaces are found to be more stable than (011) and (111). For the (310) and (311) surfaces, the relaxed surface energy is seen to oscillate back and forth between larger and smaller values as a function of surface model thickness. This result is explained by a structural transformation or phase change in the surface models of the surfaces away from c-LM. The phase change is shown by defining and determining a new quantity. Because of the phase change, the relaxed (310) and (311) surfaces are not c-LM surfaces, and the surface energies of these surfaces need to be checked for accuracy. To identify a phase change when modeling a relatively open surface of another material, such as a high-index surface, the new quantity referred to above may be useful to determine.

Surface energies of LaMnO3 high-index surfaces obtained from density-functional theory

ACS Spring Meeting 2021

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