New Insights into the Strain Coupling to Surface Chemistry, Electronic Structure, and Reactivity of La_0.7Sr_0.3MnO₃

Effects of strain on the surface cation chemistry and the electronic structure are important to understand and control for attaining fast oxygen reduction kinetics on transition-metal oxides. Here we demonstrate and mechanistically interpret the strain coupling to Sr segregation, oxygen vacancy formation, and electronic structure on the surface of La_0.7Sr_0.3MnO₃ (LSM) thin films as a model system. Our experimental results from X-ray photoelectron spectroscopy and scanning tunneling spectroscopy are discussed in light of our first principles-based simulations. A stronger Sr enrichment tendency and a more facile oxygen vacancy formation prevail for the tensile-strained LSM surface. At 500 °C in 10⁻³ mbar oxygen, both LSM film surfaces exhibit a metallic-like tunneling conductance, with a higher density of electronic states near the Fermi level on the tensile-strained LSM surface, contrary to the behavior at room temperature. Our findings illustrate the potential role and mechanism of lattice strain in tuning the reactivity of perovskite transition-metal oxides with oxygen in solid oxide fuel cell cathodes