Abhijit Pramanick

Origin of high piezoelectric response in A-site disordered morphotropic phase boundary composition of lead-free piezoelectric 0.93(Na0.5Bi0.5)TiO3-0.07BaTiO3

Perovskite piezoelectric compositions near the morphotropic phase boundary (MPB) are known to exhibit high piezoelectric response. In lead-based ABO3 compound with B-site disorder, the origin of this enhancement has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO3 compounds with A-site disorder has not been conclusively established. We describe a microscopic model derived from comparative analyses of high resolution transmission electron microscopy and neutron diffraction that explains the origin of high piezoelectric response in lead-free MPB compositions of 0.93(Na0.5Bi0.5)TiO3–0.07BaTiO3. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase are attributed to localized displacements of atoms along the non-polar directions.

Enhanced piezoelectricity and nature of electric-field induced structural phase transformation in textured lead-free piezoelectric Na0.5Bi0.5TiO3-BaTiO3 ceramics

This letter provides a comparative description of the properties of textured and randomly oriented poly-crystalline lead-free piezoelectric 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BT) ceramics. A high longitudinal piezoelectric constant of (d33) ∼ 322 pC/N was obtained in (001)PC textured NBT-7BT ceramics, which is almost ∼2× times the d33 coefficient reported for randomly oriented ceramics of the same composition. In situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nanoregions and internal stresses induced by domain switching.

Time-Resolved Characterization of Ferroelectrics Using High-Energy X-Ray Diffraction

Diffraction provides an effective means to characterize ferroelectric materials under the application of dynamic and cyclic electric fields. This paper describes a typical time-resolved diffraction setup at a synchrotron facility using high X-ray energies. Such a setup is capable of measuring the structural response of ferroelectric ceramics to electric fields of various frequencies, amplitudes, and waveforms. The use of high energies also allows the response of the sample to be measured at various angles to the applied load. The results of 3 different types of electric loading are presented and discussed: the structural response of ferroelectric ceramics to a single electric field step function, a cyclic electric field of square waveform, and a cyclic electric field of sinusoidal waveform. Each type of electric field loading provides unique information about the material behavior.

Domains, Domain Walls and Defects in Perovskite Ferroelectric Oxides: A Review of Present Understanding and Recent Contributions

Ferroelectric oxides are used in many modern technologies including sensors, actuators, thin-film memories and energy harvesting. Ferroelectrics of similar composition often show wide variations in their characteristic properties. Such variations in properties can be largely attributed to differences in the structural arrangements of domains and distributions of defects within a multidomain/polycrystalline material. Recent developments in characterization techniques and first-principle calculations have significantly advanced our understanding of how ferroelectric domains interact with material defects, and thereby influence the properties of a material. This review provides a broad outlook of the contributions from different experimental and computational studies that have clarified the structure of domains, domain walls and defects in perovskite ferroelectric oxides, and the evolution of these structures under the application of electric fields. It is intended that an integrated viewpoint of these issues, as provided here, will further motivate synergistic activities between the various research groups and industries towards the development and characterization of ferroelectric oxides.

Effect of poling on nanodomains and nanoscale structure in A-site disordered lead-free piezoelectric Na0.5Bi0.5TiO3–BaTiO3

This paper establishes the nanoscale poling mechanism operating in A-site disordered lead-free piezoelectric ceramics. Nanoscale domain maps and quantitative structural changes were obtained by deploying high-resolution transmission electron microscopy, dielectric spectroscopy, Raman spectroscopy and neutron scattering. Based on these results a microscopic model is proposed that provides insight into the E-field induced structural transformation. The stripe-like nanodomains in the unpoled system transformed into lamellar tetragonal domains with a reduced degree of displacement disorder during poling. It is proposed that the synergic effect of change in octahedral tilt disorder and cation displacement disorder leads to this transformation under an E-field. The criterion for achieving superior functional response includes stabilization of the long range order and reduction in the tilt disorder through compositional adjustments. Understanding of the poling mechanism in lead-free piezoelectric materials has been mostly limited to the behavior of domains under an applied field. However, this work provides an in-depth understanding of the changes in the local structure along with domain morphology under an applied field.

Nanoscale Atomic Displacements Ordering for Enhanced Piezoelectric Properties in Lead-Free ABO3 Ferroelectrics

In situ synchrotron X-ray diffuse scattering and inelastic neutron scattering measurements from a prototype ABO3 ferroelectric single-crystal are used to elucidate how electric fields along a nonpolar direction can enhance its piezoelectric properties. The central mechanism is found to be a nanoscale ordering of B atom displacements, which induces increased lattice instability and therefore a greater susceptibility to electric-field-induced mechanical deformation.

Strain incompatibility and residual strains in ferroelectric single crystals

Residual strains in ferroelectrics are known to adversely affect the material properties by aggravating crack growth and fatigue degradation. The primary cause for residual strains is strain incompatibility between different microstructural entities. For example, it was shown in polycrystalline ferroelectrics that residual strains are caused due to incompatibility between the electric-field-induced strains in grains with different crystallographic orientations. However, similar characterization of cause-effect in multidomain ferroelectric single crystals is lacking. In this article, we report on the development of plastic residual strains in [111]-oriented domain engineered BaTiO3 single crystals. These internal strains are created due to strain incompatibility across 90° domain walls between the differently oriented domains. The average residual strains over a large crystal volume measured by in situ neutron diffraction is comparable to previous X-ray measurements of localized strains near domain boundaries, but are an order of magnitude lower than electric-field-induced residual strains in polycrystalline ferroelectrics.

Origins of large enhancement in electromechanical coupling for nonpolar directions in ferroelectric BaTiO3

The origins of enhanced piezoelectric coupling along nonpolar crystallographic directions in ferroelectric BaTiO

Soft phonon mode dynamics in Aurivillius-type structures

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Real-space phase field investigation of evolving magnetic domains and twin structures in a ferromagnetic shape memory alloy

are investigated using in situ neutron spectroscopy. It is observed that an electric field applied away from the equilibrium polarization direction causes a stiffening of the transverse acoustic (TA) phonon branch and consequently increases interaction between the TA and the transverse optic soft mode for a range of wave vectors extending from the Brillouin zone center. This provides a direct lattice dynamics mechanism for enhanced electromechanical coupling, and could act as a guide for designing improved piezoelectric materials.