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Register a new userElectron-lattice coupling contributions to polarization switching in charge-order-induced ferroelectrics
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In this study, we carry out density functional theory calculations to elucidate the polarization switching mechanism in charge-order-induced ferroelectrics. Based on the investigations about (SrVO$_3$)$_1$(LaVO$_3$)$_1$ superlattice, we demonstrate that the charge ordering state couples strongly to lattice modes, and charge-transfer induced polarization switching has to be associated with changes of lattice distortions. Based on the type of lattice mode strongly coupled to charge ordering states, we classify the charge ordering materials in two type, namely polyhedral breathing and off-centering displacement types. We further demonstrate that only in off-centering displacement type charger ordering material, the polarization is switchable under an external field. The implications of this theory to experimental observations are also discussed and we successfully explain the different electrical behaviors in LuFe$_2$O$_4$ and Fe$_3$O$_4$. This study aims to provide guidance for searching and designing charge ordering ferroelectrics with switchable polarization.
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Consecutive stochastic 90{deg} polarization switching events, clearly resolved in recent experiments, are described by a new nucleation and growth multi-step model. It extends the classical Kolmogorov-Avrami-Ishibashi approach and includes possible consecutive 90{deg}- and parallel 180{deg}-switching events. The model predicts the results of simultaneous time-resolved macroscopic measurements of polarization and strain, performed on a tetragonal Pb(Zr,Ti)O3 ceramic in a wide range of electric fields over a time domain of five orders of the magnitude. It allows the determination of the fractions of individual switching processes, their characteristic switching times, activation fields, and respective Avrami indices.
Statistical distribution of switching times is a key information necessary to describe the dynamic response of a polycrystalline bulk ferroelectric to an applied electric field. The Inhomogeneous Field Mechanism (IFM) model offers a useful tool which allows extraction of this information from polarization switching measurements over a large time window. In this paper, the model was further developed to account for the presence of non-switchable regions in fatigued materials. Application of the IFM- analysis to bipolar electric cycling induced fatigue process of various lead-based and lead-free ferroelectric ceramics reveals different scenarios of property degradation. Insight is gained into different underlying fatigue mechanisms inherent to the investigated systems.
A stochastic model for polarization switching in tetragonal ferroelectric ceramics is introduced, which includes sequential 90{deg}- and parallel 180{deg}-switching processes and accounts for the dispersion of characteristic switching times due to a nonuniform spatial distribution of the applied field. It presents merging of the recent multistep stochastic mechanism (MSM) with the earlier nucleation limited switching (NLS) and inhomogeneous field mechanism (IFM) models. The new model provides a much better description of simultaneous polarization and strain responses over a wide time window and a deeper insight into the microscopic switching mechanisms, as is exemplarily shown by comparison with measurements on lead zirconate titanate.
The atomic-level control achievable in artificially-structured oxide superlattices provides a unique opportunity to explore interface phases of matter including high-density 2D electron gases. Electronic-structure calculations show that the charge distribution of the 2D gas is strongly modulated by electron-phonon interactions with significant ionic polarization. Anharmonic finite-temperature effects must be included to reproduce experiment. Density functional perturbation theory is used to parameterize a simple model introduced to represent these effects and predict temperature dependencies.
Using density-functional calculations we study the structure and polarization response of tetragonal PbTiO3, BaTiO3 and SrTiO3 in a strain regime that is previously overlooked. Different from common expectations, we find that the polarizations in all three substances saturate at large strains, demonstrating a universal phenomenon. The saturation is shown to originate from an unusual and strong electron-ion correlation that leads to cancellation between electronic and ionic polarizations. Our results shed new insight on the polarization properties, and reveal the existence of a fundamental limit to the strain-induced polarization enhancement.
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