Polarization dependence of elastic and electrostatic driving forces to dopant segregation on LaMnO3 Dopant segregation is a common degradation preferred lattice size of the dopant versus the host lattice. The pathway on perovskite oxide surfaces in electrostatic energy arises from the attraction of the negatively charged dopants (D2+ on a La site) to the surface enriched3+ energy conversion applications. Here we with positively charged oxygen vacancies (V¨). Nevertheless, O focus on resolving quantitatively how it is currently unclear how positive or negative potentials dopant segregation is affected by oxygen affects the two driving forces and there are a lot of conflicting results in the literature. One difficulty in the study of dopant2,3 chemical potential, which varies over a segregation arises from the fact that segregation kinetics and wide range in electrochemical energy thermodynamics cannot be easily separated. In addition, bulk conversion reactions. We found that the two and surface contributions to segregation are not independent of each other. Such complexities in dopant segregation lead to a known driving forces of dopant segregation, large number of material parameters (such as composition and electrostatic and elastic energies of dopant, microstructure) and process parameters (such as temperature, changed with oxygen chemical potential oxygen partial pressure, and applied potential) that have been shown to influence segregation. in an opposite way and that this caused a transition between the electrostatically and LATERAL POLARIZATION METHOD elastically dominated segregation regimes. In the present study, we employ a recently developed electrochemical Such segregation behavior was evidenced cell configuration utilizing a polarization gradient across a thin-4 by in-situ XPS performed at SOLEIL film electrode to obtain a large range of anodic or cathodic oxygen chemical potentials on one single sample (Figure 1). Synchrotron. This not only saves time, but also eliminates possible variations between experimental conditions and sample history, which can Perovskite oxides (ABO) are considered key players in clean differ slightly between samples and preparations. Moreover, 3 the geometry of the cell enabled us to perform in-situ XPS energy conversion applications, including in solid oxide fuel/ electrolysis cells (SOF/ECs). Many state-of-the-art perovskites, measurement while applying polarization to the sample through such as LaSrMnO, suffer from degradation of their surface the open sample surface. 1-x x 3 chemistry and oxygen exchange kinetics at high temperatures FIGURE 1 from 700°C to 1000°C under cell voltages, which can approach over 1 V. This process limits their long-term stability in the aforementioned applications. This degradation is primarily because of dopant segregation to the surface and precipitation as insulating phases, such as SrO. These insulating surface x layers block the electron transfer and oxygen exchange pathways, reducing the attainable power densities. It is thus important to resolve the reasons of dopant segregation under the SOF/ EC operation conditions in order to increase the long-term efficiency of the cells. Elastic (E) and electrostatic (Eela elec) energies of the dopant in the perovskite latticeare the two well-known driving forces1 of dopant segregation reported in the literature. The elastic contribution originates from the mismatch between the 42