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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 33: Focus Session: (Multi-)Ferroic States V
KFM 33.1: Vortrag
Freitag, 22. März 2024, 09:30–09:50, EMH 225
Landau free energy of PbTiO3 from atomistic simulations — •Mauro Pulzone1, 2, Natalya S. Fedorova1, Hugo Aramberri1, and Jorge Íñiguez-González1, 2 — 1Luxembourg Institute of Science and Technology, Esch-sur-Alzette, Luxembourg — 2University of Luxembourg, Esch-sur-Alzette, Luxembourg
In this study we introduce a methodology to identify and compute, from atomistic simulations, the simplest Landau potential that accurately describes the static properties of PbTiO3 as a function of temperature. The free energy of the system is expanded around the reference cubic phase in powers of the polarization. We consider all possible combinations of symmetry-allowed terms from 2nd up to 10th order. We fit all these models using the approach of Ref. [Phys. Rev. B 63, 144103 (2001)], taking as input the data obtained from Monte Carlo simulations based on the atomistic second-principles model for PbTiO3 proposed by Wojdeł et al. [Phys.: Condens. Matter 25, 305401 (2013)].
We find that a 6th-order expansion is sufficient to capture the system’s behavior, including the first-order character of the transition. Moreover, as the temperature increases (hundreds of Kelvins above the phase transition) a 4th-order model is enough to reproduce the atomistic data accurately.
Presently we are extending this work to explicitly consider the strain as an order parameter, as the elastic deformation of the cell is known to play an essential role in the first-order character of the phase transition of PbTiO3 [Phys. Rev. B 55, 6161 (1997)].
Keywords: Landau Theory; Lead titanate; Symmetry; Ferroelectric; Perovskite