Dresden 2026 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 15: Phase Transformations I

MM 15.3: Talk

Tuesday, March 10, 2026, 14:30–14:45, SCH/A215

Coupled phase transition and valence fluctuations in Fe-doped BaTiO₃: a combined DFT and DMFT study — •Zhiyuan Li, Ruiwen Xie, and Hongbin Zhang — Institute of Materials Science, TU Darmstadt, 64287 Darmstadt Germany

Rational control of structural phase transitions in perovskites is a key challenge in materials design. In Fe-doped BaTiO₃(BTO), experiments observe a tetragonal-to-hexagonal transition, yet the governing microscopic mechanisms remain unclear. A critical control parameter is the Goldschmidt tolerance factor, which relies intimately on the dopant ionic radius and, consequently, the valence state. However, the valence of Fe in BTO remains a long-standing open question, with conflicting reports necessitating a treatment beyond standard DFT. Here, we employ Density Functional Theory (DFT) combined with Dynamical Mean-Field Theory (DMFT) to investigate this interplay. DMFT reveals that the Fe dopant exhibits strong valence and spin fluctuations, which are significantly suppressed by oxygen vacancies to stabilize a high-spin state. Integrating these electronic insights, our total-energy calculations identify three cooperative mechanisms driving the phase transition: tolerance factor variations, Jahn-Teller distortions, and oxygen vacancy formation. Then a systematic quantitative analysis was performed on these three factors. These findings provide a unified microscopic understanding of defect-mediated phase control.

Keywords: Fe-doped BaTiO3; DFT+DMFT; Phase transition; Valence fluctuations