Ferroelectricity in crystals is associated with the displacement of ions or rotations of polar units. Here we consider the dipole created by donor doping (D+) and the corresponding bound polaron (e-). A dipole of 6.15 Debye is predicted, from Berry phase analysis, in the Ruddlesden-Popper phase of Sr3Ti2O7. A characteristic double-well potential is formed, which persists for high doping densities. The effective Hubbard U interaction can vary the defect state from metallic, a two-dimensional polaron, through to a zero-dimensional polaron. The ferroelectriclike behavior reported here is localized and distinct from conventional spontaneous lattice polarization.
Bibliographical noteFunding Information:
Funding was received from the Yoshida Scholarship Foundation and Japan Student Services Organization. This work was also supported by the core-to-core collaboration funded by EPSRC (EP/R034540-1) and JSPS (JPJSCCA20180006). Via our membership of the UK’s HEC Materials Chemistry Consortium, funded by EPSRC (EP/L000202 and EP/P020194), this work used the ARCHER2 Supercomputing Service.
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