Electron polaron at neutral 180 ∘ domain wall in PbTiO 3 : Stability, trapping energies, and transverse polarization

We use density functional theory with a Hubbard correction to investigate Ti-centered electron polarons at neutral PbO-centered 180 ∘ domain walls in tetragonal PbTiO 3 . The Hubbard parameter for Ti 3 d states is determined using the finite-size-corrected polaronic energy-level alignment procedure, yielding stable electron-polaron formation in bulk PbTiO 3 with a trapping energy of − 0.06 eV . In the domain-wall supercell, the excess electron localizes on a Ti site and forms a Ti 3 + center with an occupied in-gap d x y state. Comparison of bulk-like and near-wall Ti sites shows that their trapping energies differ by only about 0.01 eV, indicating that this neutral domain wall does not provide a significant thermodynamic driving force for electron-polaron segregation. While the Ising-like reversal of the out-of-plane polarization is preserved, the localized electron induces a finite transverse polarization component normal to the wall, enhancing a local Néel-like distortion that is strongest when the polaron is located at the wall. These results show that neutral 180 ∘ domain walls in PbTiO 3 do not substantially alter the stability of Ti-centered electron polarons, but they can couple to the polaron-induced lattice distortion through a localized transverse polarization response.