arXiv subjects

Sabine Körbel

Publications and source records attributed to Sabine Körbel.

6 recordsLinked to original sources

arXiv2025

Energy profile and hopping barriers for small electron polarons at ferroelectric domain walls in bismuth ferrite from first principles

Evidence from first-principles calculations indicates that excess electrons in BiFeO$_3$ form small polarons with energy levels deep inside the electronic band gap. Hence, $n$-type electronic transport could occur by hopping of small electron polarons rather than by band-like transport. Here, by means of first-principles calculations, small electron polaron hopping in BiFeO$_3$ is investigated. Both bulk BiFeO$_3$ and a typical ferroelectric domain wall, the neutral 71° domain wall, are considered. The latter is included to account for experimental observations of electrical conductivity at domain walls in otherwise insulating ferroelectrics. The object of this study is to shed light on the intrinsic electron conduction in rhombohedral BiFeO$_3$ and the effect of pristine neutral ferroelectric domain walls. The computed energy barriers for small electron polaron hopping are near 0.2 eV, similar to other perovskite oxides, both in the bulk and within the neutral 71° domain wall. Trapping energies of small electron polarons at the three prevalent domain walls, the 71°, the 109°, and the 180° wall, were determined. The domain walls are found to act as two-dimensional traps for small electron polarons, with a trap depth of about two times the thermal energy at room temperature. Based on these findings, the intrinsic $n$-type mobility and the diffusion constant in BiFeO$_3$ at room temperature are estimated, and experimental conductivity data for BiFeO$_3$ are discussed.

cond-mat.mtrl-sci↗

arXiv2025

Erratum: Photovoltage from ferroelectric domain walls in BiFeO$_3$

In the original article a mistake in the methodology lead to an incorrect prediction of exciton delocalization below a critical exciton density. This unrealistic delocalized exciton state yielded a sizable domain-wall photovoltage. When done correctly, the simulations yield self-trapped (localized) excitons at all considered exciton densities, without any evidence for a transition to a delocalized exciton. This realistic self-trapped exciton state yields only a negligible domain-wall photovoltage. The original conclusion that ferroelectric domain walls could be responsible for the measured photovoltage if carrier lifetime and diffusion length are higher than expected is incorrect. Correct is: The domain-wall photovoltage in BiFeO3 is much too small to explain the measured photovoltage. The original analysis is meaningful for ferroelectrics without carrier self-trapping, not for BiFeO3.

cond-mat.mtrl-sci↗

arXiv2023

Optical signatures of defects in BiFeO$_3$

Optical absorption in rhombohedral BiFeO$_3$ starts at photon energies below the photoemission band gap of $\approx$ 3 eV calculated from first principles. A shoulder at the absorption onset has so far been attributed to low-lying electronic transitions or to oxygen vacancies. In this work optical spectra are calculated ab initio to determine the nature of the optical transitions near the absorption onset of pristine BiFeO$_3$, the effect of electron-hole interaction, and the spectroscopic signatures of typical defects, i.e. doping (excess electrons or holes), intrinsic defects (oxygen and bismuth vacancies), and low-energy structural defects (ferroelectric domain walls).

cond-mat.mtrl-sci↗

arXiv2022

Zig-zag charged domain walls in ferroelectric PbTiO$_3$

We report a theoretical investigation of a charged 180$^\circ$ domain wall in ferroelectric PbTiO$_3$, compensated by randomly distributed immobile charge defects. For this we utilize atomistic shell-model simulations and continuous phase-field simulations in the framework of the Ginzburg-Landau-Devonshire model. We predict that domain walls form a zig-zag pattern and we discuss its properties in a broad interval of compensation-region widths, ranging from a couple to over a hundred nanometers.

cond-mat.mtrl-sci↗

arXiv2022

Transition between large and small electron polaron at neutral ferroelectric domain walls in BiFeO$_3$

Ferroelectric domain walls are planes within an insulating material that can accumulate and conduct charge carriers, hence the interaction of the domain walls with the charge carriers can be important for photovoltaic and other electronic applications. By means of first principles calculations we predict a transition from a large two-dimensional electron polaron to a small polaron at the domain walls at a critical electron density, with polaron signatures in optical absorption and photoluminescence. We find that large and small polarons at the domain walls create different absorption peaks within the band gap that are not present in the case of pristine domain walls. These are an extended Drude peak in the case of large electron or hole polarons and a narrow mid-gap peak in the case of the small electron polaron.

cond-mat.mtrl-sci↗

arXiv2018

Electron trapping by neutral pristine ferroelectric domain walls in BiFeO$_3$

First-principles calculations for pristine neutral ferroelectric domain walls in BiFeO$_3$ reveal that excess electrons are selectively trapped by the domain walls, while holes are only weakly attracted. Such trapped excess electrons may be responsible for the thermally activated electrical conductivity at domain walls observed in experiments. In the case of a periodic array of domain walls, the trapped excess electrons create a zigzag potential, whose amplitude depends on the electron concentration in the material and the domain-wall distance. The potential is asymmetric for 71° and 109° domain walls. This could modify the open-circuit voltage in a solar cell and hence influence the photoelectric effect in BiFeO$_3$.

cond-mat.mtrl-sci↗