IMF2017

The perovskite BaTiO₃, which presents a tetragonal structure at room temperature, has its bulk polarization along the c-axis or the a-axes. For out-of-plane (perpendicular to the surface) polarized domains, the surface discontinuity leads to fixed polarization charge which in turn modifies the electrostatic surface potential. Charge-screening can alter the magnitude and sign of the surface potential. For example, unscreened and fully screened surfaces show opposite surface potential for the same underlying polarization. The surface potential may be further modulated at the surface where the atomic distortions associated with the ferroelectric (FE) state can be considerably altered. One recent report suggests that in BaTiO₃ the signature of surface domain ordering may persist well above the Curie temperature (T_C). The aim of the present study is to improve our understanding of how surface charge and polar adsorbates interact to influence domain order below, during and above the FE-PE phase transition. We have used PhotoElectron Emission Microscopy to study the evolution of the surface charge and domain structure in BaTiO₃(001) during the ferroelectric-paraelectric phase transition. At room temperature, in- and out-of-plane polarized domains are observed with ferroelectric and ferroelastic domain walls. Strong adsorbate screening is present resulting in inversion of the electrostatic surface potential contrast. Domain-related surface charge above T_C is still observable. Ferroelectric memory effects persist up to at least 550°C. The domain-like surface structures above T_C may be due to a combination of atomic relaxation, residual adsorbates and oxygen vacancies near domain walls.