Dresden 2020 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 11: Ferroics - Domains and Domain Walls (joint session KFM/MA)
KFM 11.3: Vortrag
Mittwoch, 18. März 2020, 15:40–16:00, TOE 317
Soft modes and effective Hamiltonian for the antiferroelectric NaNbO3 — •Niloofar Hadaeghi and Hongbin Zhang — Institute of Materials Science, TU Darmstadt, 64287 Darmstadt, Germany
To understand the antiferroelectric(AFE) phase transition in prototype NaNbO3, we carried out detailed symmetry analysis and first-principles calculations. The primary modes have been identified together with the coupling terms up to the fourth order based on symmetry. The corresponding energy landscape is obtained by constraint calculations with specific mode(s) frozen-in, and is further fitted to get the effective Hamiltonian. It is observed that there are three dominant modes for the AFE phase of NaNbO3; R5−, T2, and Δ5. Our results reveal that it is not possible for the system to adopt the coupling of R5− and T2 modes, since there is a strong mutual repulsion between them. However, coupling of both R5− and Δ5, and T2 and R5− are essential in the reduction of energy. Theses couplings are cooperative to stabilize the AFE phase. That is, the trilinear coupling is essential for the occurrence of the AFE phase. We also investigated the unfolded band structure to understand the effects of such soft modes on the electronic structure.