IN-SITU XPS MEASUREMENT ON LaSrMnO0.8 0.2 3 PHYSICOCHEMISTRY OF LIQUIDS, With the lateral polarization method, in-situ APXPS measurements were SOFT MATTER, NANOCHEMISTRY performed for cathodically biased LaSrMnO (LSM) at the synchrotron SYNCHROTRON SOLEIL HIGHLIGHTS 2020 0.8 0.2 3 beamline TEMPO at SOLEIL. The measurement was done at 650°C in an atmosphere of 100mTorr O. The potential distribution within the2 LSM film during the application of -0.75 V to the working electrode is TEMPO BEAMLINE illustrated in Figure 2a and b by comparing the peak positions of the La 4d spectra at the spots selected for measuring the potential effects. Associated publication Moreover, the development of the Sr 3d components at high temperature Electrochemical Polarization are summarized in Figure 2c. The result clearly shows a progressive Dependence of the Elastic and enhancement of Sr segregation with increasing negative bias. Electrostatic Driving Forces to Aliovalent Dopant Segregation on Further experiments were done ex-situ with different perovskite oxides LaMnO.3 in a wider range of polarization. We examined the dopant segregation D. Kim, R. Bliem, F. Hess, for three compounds with different dopant cation sizes; LaDMnO0.8 0.2 3 J.-J. Gallet & B. Yildiz. (LDM, D=Ca, Sr, Ba). By selecting the three dopant cations, Ca, Sr, and Ba, with the same charge (2+) but different cation sizes, we probed the J. Am. Chem. Soc., 142, 3548 (2020). effects of Eela created by the dopants’ size mismatch with respect to the host cation La while keeping E3+ nearly constant. Figure 3b and References elec c show a U-shaped dependency of the amount of dopant segregation [1] W. Lee et al., Journal of the as a function of polarization by XPS for Sr and Ba. This result can be American Chemical Society 135, interpreted that E increases with anodic polarization while Eela elecincreases 7909 (2013). with cathodic polarization. In the case of Ca, dopant enrichment at the [2] G. J. la O’ et al., Journal of The surface is observed only in the cathodic polarization range due to its Electrochemical Society 156, B771 negligible E. The minimum of the U-shaped curve is interpreted asela (2009). the transition point between the two driving forces, E and E and it [3] A.-K. Huber et al., Journal of elec ela Catalysis 294, 79 (2012). shifts to higher oxygen chemical potential with increasing dopant cation [4] T. M. Huber et al., Journal of The radius (RBa > R > R).Sr Ca Electrochemical Society 164, F809, FIGURE 2 (2017). Corresponding author Bilge Yildiz Department of Materials Science and Engineering, Massachusetts Institute of Technology. byildiz@mit.edu FIGURE 3 Captions FIGURE 1: Illustration of the experimental setup designed for applying a continuous polarization gradient across the top electrode surface. The bias voltage applied between the two Pt electrodes leads to a monotonous decrease of the voltage difference applied across the LDM film, illustrated with the schematic potential-distance plot. FIGURE 2: La 4d spectra acquired at 650°C in five different positions illustrating the gradual change in polarization across the surface: (a) overview (b) zoomed- in view. (c) Sr 3d spectra acquired at five different positions, corresponding to a different voltage shown in the graph. FIGURE 3: XPS intensity of surface a) Ca, b) Sr, and c) Ba components, normalized by the total intensity of A-site cations of LDM. 43