Perovskites exhibit outstanding performance in applications such as photocatalysis, electrochemistry, or photovoltaics, yet their practical use is hindered by the instability of these materials under operating conditions, specifically caused by the segregation of alkali cations toward the surface. The problem arises from the bulk strain related to different cation sizes, as well as the inherent electrostatic instability of perovskite surfaces. Here, we focus on atomistic details of the surface-driven process of interlayer switching of alkali atoms at the inorganic perovskite surface. We show that the (001) surface of KTaO3 cleaved at room temperature contains equally populated TaO2 and KO terminations, while the uncompensated polarity of these terminations promotes diffusion of KO from the subsurface toward the topmost surface layer at temperatures as low as 200 °C. This effect is directly probed at the atomic scale by Atomic Force Microscopy and the chemical properties of the resulting surfaces are investigated by the adsorption of CO and H2O. The experiments indicate that KO segregation is associated with the formation of K and O vacancies in the near-surface region, which is further supported by depth-dependent X-ray Photoelectron Spectroscopy measurements and Density Functional Theory calculations. Our study shows that the KO segregation influences the surface reactivity both toward CO and water, which was probed at the atomic scale.

CNR Istituto Officina dei Materiali Trieste 34149 Italy

Department of Polymers and Advanced Materials Centro de Física de Materiales University of the Basque Country UPV EHU San Sebastián 20018 Spain

Department of Surface and Plasma Science Charles University Prague 18000 Czech Republic

Dipartimento di Fisica e Astronomia Università di Bologna Bologna 40126 Italy

Faculty of Physics and Center for Computational Materials Science University of Vienna Sensengasse 8 12 Vienna 1090 Austria

International Center for Quantum Materials School of Physics Peking University Beijing 100871 China

Marian Smoluchowski Institute of Physics Jagiellonian University Krakow 30 348 Poland

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