Why hole polaron formation on oxygen is limiting the Fermi level in Fe acceptor doped BaTiO3 under oxidizing conditions
Abstract
Oxidizing Fe-doped BaTiO3 is commonly expected to convert substitutional Fe3+ acceptors into formal Fe4+ centers. Yet, the experimentally accessible picture based on electron-paramagnetic resonance (EPR) is dominated by Fe3+-related signatures, while Fe4+ is not a straightforward observable. Here we show that this apparent discrepancy reflects the preferred location of the oxidizing hole: not on Fe, but on oxygen. Using density-functional theory with with occupation-matrix control and a piecewise-linearity-based Hubbard correction (DFT+U) for O-2p states, we find that an oxygen-centered hole polaron is forming a Fe3+-O− complex that is lower in energy than the formal Fe4+ configuration. Our results identify ligand-hole formation as a favorable charge-compensation mechanism in oxidized Fe-doped BaTiO3 and provide an explanation for the predominance of Fe3+-based centers in spectroscopy. More broadly, they show how oxygen polarons can limit Fermi-level shifts and control the electronic response of acceptor-doped ferroelectric perovskites.
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BibTeX
@misc{amirabbasi2026hole,
title = {{Why hole polaron formation on oxygen is limiting the Fermi level in Fe acceptor doped BaTiO$_3$ under oxidizing conditions}},
author = {Mohammad Amirabbasi and Emre Erdem and Denis Sudarikov and Jochen Rohrer and Andreas Klein and Karsten Albe},
howpublished = {arXiv},
year = {2026},
month = may,
doi = {10.48550/arxiv.2605.18258},
eprint = {2605.18258},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.18258},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Why hole polaron formation on oxygen is limiting the Fermi level in Fe acceptor doped BaTiO_3 under oxidizing conditions
AU - Mohammad Amirabbasi
AU - Emre Erdem
AU - Denis Sudarikov
AU - Jochen Rohrer
AU - Andreas Klein
AU - Karsten Albe
PY - 2026
DA - 2026/05/18
PB - arXiv
DO - 10.48550/arxiv.2605.18258
UR - https://arxiv.org/abs/2605.18258
AB - Oxidizing Fe-doped BaTiO_3 is commonly expected to convert substitutional Fe^3+ acceptors into formal Fe^4+ centers. Yet, the experimentally accessible picture based on electron-paramagnetic resonance (EPR) is dominated by Fe^3+-related signatures, while Fe^4+ is not a straightforward observable. Here we show that this apparent discrepancy reflects the preferred location of the oxidizing hole: not on Fe, but on oxygen. Using density-functional theory with with occupation-matrix control and a piecewise-linearity-based Hubbard correction (DFT+U) for O-2p states, we find that an oxygen-centered hole polaron is forming a Fe^3+-O^− complex that is lower in energy than the formal Fe^4+ configuration. Our results identify ligand-hole formation as a favorable charge-compensation mechanism in oxidized Fe-doped BaTiO_3 and provide an explanation for the predominance of Fe^3+-based centers in spectroscopy. More broadly, they show how oxygen polarons can limit Fermi-level shifts and control the electronic response of acceptor-doped ferroelectric perovskites.
ER -