The variation in the surface potential as a function of the ferroelectric polarization of micron scale domains in a thin epitaxial film of Pb(Zr0.48Ti0.52)O3 is measured using mirror electron microscopy. Domains were written using piezoforce microscopy. The surface potential for each polarization was deduced from the mirror to low energy electron microscopy transition in the local reflectivity curve. The effect of extrinsic screening of the fixed polarization charge at the ferroelectric surface is demonstrated. The results are compared with density functional theory calculations.

At ferroelectric longitudinal domain walls there is an uncompensated charge, which could form a twodimensional electron gas in the insulator. However, the uncompensated charges can be accommodated by, e.g., defects or localized states that split off from the conduction band. We carried out density functional theory calculations to study these scenarios in PbTiO 3 with and without consideration of strong correlation effects simulated via inclusion of a Hubbard parameter U. The optimized structure and electronic structure depend on the choice of this parameter: For vanishing U , a broad, conducting domain wall is obtained, while increasing U leads to localized Ti 3d states and an insulating, sharp domain wall. We also investigated the effects of varying the ferroelectric polarization on the electronic structure of these domain walls.

The polar-to-nonpolar interface of DyScO 3 and SrTiO 3 was studied using density functional theory. Due to the polar discontinuity arising from nominally charged DyO or ScO 2 layers, sharp interfaces induce a strong ferroelectriclike polarization in the SrTiO 3 , while in chemically mixed interfaces this discontinuity is avoided and no such polarization can be found. In both scenarios the interface remains insulating with only a small reduction of the band gap. Our calculations show that mixed interfaces are energetically more favorable than sharp ones, in agreement with recent experimental results that confirmed intermixing at these interfaces.

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