Showing papers by "Somnath Choudhury published in 2008"
TL;DR: An approach is developed to visualize the nucleation centres controlling polarization switching processes with nanometre resolution, determine their spatial and energy distribution and correlate them to local microstructure, using random-bond and random-field components of the disorder potential.
Abstract: Macroscopic ferroelectric polarization switching, similar to other first-order phase transitions, is controlled by nucleation centres. Despite 50 years of extensive theoretical and experimental effort, the microstructural origins of the Landauer paradox, that is, the experimentally observed low values of coercive fields in ferroelectrics corresponding to implausibly large nucleation activation energies, are still a mystery. Here, we develop an approach to visualize the nucleation centres controlling polarization switching processes with nanometre resolution, determine their spatial and energy distribution and correlate them to local microstructure. The random-bond and random-field components of the disorder potential are extracted from positive and negative nucleation biases. Observation of enhanced nucleation activity at the 90 composite function domain wall boundaries and intersections combined with phase-field modelling identifies them as a class of nucleation centres that control switching in structural-defect-free materials.
255 citations
TL;DR: Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant.
Abstract: Direct measurement of the remanent polarization of high quality (001)-oriented epitaxial BiFeO3 thin films shows a strong strain dependence, even larger than conventional (001)-oriented PbTiO3 films. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant.
222 citations
TL;DR: In this article, the effects of various types of substrate constraint on the domain morphologies of BiFeO3 thin films were systematically analyzed and the dependence of the {110}c-type domain wall orientation on substrate constraint was also discussed.
Abstract: Ferroelectric domain structures of (001)c, (101)c, and (111)c oriented epitaxial BiFeO3 thin films were studied by using the phase-field approach. Long-range elastic and electrostatic interactions were taken into account. The effects of various types of substrate constraint on the domain morphologies were systematically analyzed. It is demonstrated that domain structures of BiFeO3 thin films could be controlled by selecting proper film orientations and substrate constraint. The dependence of the {110}c-type domain wall orientation on substrate constraint for the (001)c oriented BiFeO3 thin film was also discussed.
64 citations
TL;DR: In this paper, the authors show that the threshold field for moving an antiparallel ferroelectric domain wall dramatically drops by two to three orders of magnitude if the wall was diffuse by only ∼ 1-2 nm.
Abstract: Unlike ideal 180° ferroelectric walls that are a unit cell wide (∼0.5 nm), real walls in ferroelectrics have been reported to be many nanometers wide (1–10 nm). Using scanning nonlinear dielectric microscopy of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) ferroelectrics, we show that the wall width at surfaces can vary considerably and even reach ∼100 nm in places where polar defects adjoin a wall. The consequence of such variable wall widths is investigated on the specific property of threshold field required for wall motion. Using microscopic phase-field modeling, we show that the threshold field for moving an antiparallel ferroelectric domain wall dramatically drops by two to three orders of magnitude if the wall was diffuse by only ∼1–2 nm, which agrees with experimental wall widths and threshold fields for these materials. Modeling also shows that wall broadening due to its intersection with a surface will influence the threshold field for wall motion only for very thin films (1–10 nm) whe...
48 citations
TL;DR: In this article, the coercive fields and remanent polarizations of (001)-oriented epitaxial barium titanate thin films using the phase-field approach were studied. But, the effect of strain on the coercive field was not investigated.
Abstract: Strain is generally known to increase the coercive field of a ferroelectric thin film as compared to a stress-free single crystal or a strain-relaxed film. We studied the coercive fields and remanent polarizations of (001)-oriented epitaxial barium titanate thin films using the phase-field approach. It is demonstrated, while the remanent polarization decreases as in-plane strain changes from being compressive to tensile, the variation of coercive field with strain is complicated. We noted more than two times drop in coercive field with a reduction of compressive strain of only ∼0.05%, which we attribute to the existence of multiple ferroelectric phases.
45 citations
TL;DR: In this paper, the effect of anisotropic strains on the phase transitions and domains structures of BaTi03 thin films was studied using both thermodynamic calculations and phase-field simulations.
Abstract: The effect of anisotropic strains on the phase transitions and domains structures of BaTi03 thin films was studied using both thermodynamic calculations and phase-field simulations. The misfit strain -misfit strain domain stability diagrams, i.e. the graphical representations of stable ferroelectric phases and domain structures as a function of strains, were predicted. The similarity and significant differences between the diagrams from thermodynamic calculations assuming single domains and from phase-field simulations were analyzed. Typical domain structures as a result of anisotropic misfit strains are presented.
44 citations
TL;DR: In this article, the influence of dislocations, located at the interface of a ferroelectric film and its underlying substrate, on the Ferroelectric hysteresis loop including the remanent polarization and coercive field using phase-field simulations was investigated.
Abstract: We investigated the influence of dislocations, located at the interface of a ferroelectric film and its underlying substrate, on the ferroelectric hysteresis loop including the remanent polarization and coercive field using phase-field simulations. We considered epitaxial ferroelectric BaTiO3 films and found that the hysteresis loop is strongly dependent on the type and density of interfacial dislocations. The dislocations that stabilize multiple ferroelectric variants and domains reduce the coercive field, and consequently, the corresponding remanent polarization also decreases.
43 citations
TL;DR: In this paper, the domain stability and domain structures of (001)-oriented PbTiO3 ferroelectric thin films subject to anisotropic in-plane strains were studied using phase-field method.
Abstract: The domain stability and domain structures of (001)-oriented PbTiO3 ferroelectric thin films subject to anisotropic in-plane strains were studied using phase-field method. Based on the simulation results, a room temperature domain/phase stability diagram was constructed for PbTiO3 thin films with the in-plane strains ranging from −5% to 5%. The predicted diagram is both quantitatively and qualitatively different from those obtained using thermodynamic calculations based on a single-domain assumption.
37 citations
TL;DR: In this article, local polarization switching in epitaxial ferroelectric thin films in the presence of ferroelastic domain walls was studied using phase-field approach and the nucleation bias profile across a twin wall was analyzed, and the localization of preferential nucleation sites was established.
Abstract: Local polarization switching in epitaxial ferroelectric thin films in the presence of ferroelastic domain walls was studied using phase-field approach The nucleation bias profile across a twin wall was analyzed, and the localization of preferential nucleation sites was established This analysis was further extended to a realistic domain structure with multiple twin boundaries It was observed that the local nucleation voltage required for a 180° domain switching is closely related to the number of such local defects
36 citations
TL;DR: In this article, a three-dimensional phase-field model was developed for studying domain structures in ferroelectric islands attached onto a substrate, which simultaneously takes into account the long-range electric and elastic interactions, substrate constraint, as well as the stress relaxation caused by the surfaces of an island.
Abstract: A three-dimensional phase-field model was developed for studying domain structures in ferroelectric islands attached onto a substrate. It simultaneously takes into account the long-range electric and elastic interactions, substrate constraint, as well as the stress relaxation caused by the surfaces of an island. The phase-field simulations demonstrated that the domain structures of ferroelectric islands could be dramatically different from those of continuous thin films due to the change of stress state. The stress distribution inside islands is highly dependent on the aspect ratio of the islands. It provides us an effective way for engineering the domain structures of ferroelectric materials.
28 citations
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TL;DR: In this paper, the authors show that the threshold field for moving an ideal antiparallel ferroelectric wall dramatically drops by 2-3 orders of magnitude if the wall were diffuse by only 2 -3nm.
Abstract: While an ideal antiparallel ferroelectric wall is considered a unit cell in width (~0.5nm), we show using phase field modeling that the threshold field for moving this wall dramatically drops by 2-3 orders of magnitude if the wall were diffuse by only ~2-3nm. Since antiparallel domain walls are symmetry allowed in all ferroelectrics, and since domain wall broadening on nanometer scale is widely reported in literature, this mechanism is generally applicable to all ferroelectrics.
02 Dec 2008
TL;DR: In this article, the authors reported the strain dependence of remanent polarization and coercive field of epitaxial (001)p BiFeO3 films and achieved a fatigue-free switching behavior to 1010 cycles.
Abstract: We report the strain dependence of remanent polarization and coercive field of epitaxial (001)p BiFeO3 films. Our measurements reveal that the large spontanoues polarization of BiFeO3 is indeed intrinsic, the remanent polarization of (001)p BiFeO3 thin films has a strong strain dependence, even stronger than (001) PbTiO3 films, and the coercive field of BiFeO3 films is also tunable. In addition, the low coercive filed and the reduced leakage current in (001)p BiFeO3 membranes allows us to achieve a fatigue-free switching behavior to 1010 cycles. This experimental result strongly suggests that epitaxial (001)p BiFeO3 thin films are very promising materials for non-volatile memories and magnetoelectric devices.