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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 4: (Multi)ferroic States: From Fundamentals to Applications (II)
KFM 4.5: Vortrag
Montag, 17. März 2025, 12:30–12:45, H9
Coupling between small polarons and ferroelectricity in BaTiO3 — •Darin Joseph1 and Cesare Franchini1,2 — 1Dipartimento di Fisica e Astronomia, Università di Bologna, 40127 Bologna, Italy — 2University of Vienna, Faculty of Physics, Center for Computational Materials Science, Vienna, Austria
Ferroelectric properties of materials are found to be modified upon polaron formation. In this study, we investigate the formation of electron and hole small polarons in the prototypical ferroelectric material barium titanate (BaTiO3), with a focus on their interaction with ferroelectric distortive fields. To accurately describe the ferroelectric phase in BaTiO3, we employ the HSE06 hybrid functional, which addresses the limitations of conventional DFT and DFT+U models, providing a more precise depiction of both ferroelectric and polaronic behaviours. Our analysis spans three structural phases of BaTiO3: cubic, tetragonal, and rhombohedral. We uncover a phase-dependent trend in electron polaron stability, which progressively increases across the structural phases, peaking in the rhombohedral phase due to the constructive coupling between the polaron and ferroelectric phonon fields. In contrast, hole polarons exhibit a stability pattern largely unaffected by the phase transitions. Furthermore, we observe that polaron self-trapping significantly alters the local ferroelectric distortive pattern, which propagates to neighbouring sites but has a minimal effect on the long-range macroscopic spontaneous polarization. Charge trapping is also associated with localized spin formation, opening new possibilities for enhanced functionalities in multiferroic materials.
Keywords: Ferroelectricity; Polaron; BaTiO3; HSE06; Multiferroics