Atomic scale symmetry and polar nanoclusters in the paraelectric phase of ferroelectric materials

Abstract

The nature of the “forbidden” local- and long-range polar order in nominally non-polar paraelectric phases of ferroelectric materials has been an open question since the discovery of ferroelectricity in oxide perovskites, ABO3. A currently considered model suggests locally correlated displacements of B-site atoms along a subset of <111> cubic directions. Such off-site displacements have been confirmed experimentally; however, being essentially dynamic in nature they cannot account for the static nature of the symmetry-forbidden polarization implied by the macroscopic experiments. Here, in an atomically resolved study by aberration-corrected scanning transmission electron microscopy complemented by Raman spectroscopy, we reveal, directly visualize and quantitatively describe static, 2–4 nm large polar nanoclusters in the nominally non-polar cubic phases of (Ba,Sr)TiO3 and BaTiO3. These results have implications on understanding of the atomic-scale structure of disordered materials, the origin of precursor states in ferroelectrics, and may help answering ambiguities on the dynamic-versus-static nature of nano-sized clusters.

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering

“…Note that much better Sig and R w values are observed for x = 0.10 using an R–O–T phase model that those observed using a pure cubic phase (Table S1), illustrating the existing local polar symmetries inside the macroscopic pseudo-cubic symmetry, which is further confirmed by the well-fitted results of the phase fraction (Figure g). Similar phenomena were also observed in other lead-free piezoceramics. − In addition, O and T phases almost equally share the phase fraction at x = 0, which is consistent with the similar intensities of (002) pc and (200) pc peaks (Figure g). The fraction of the T phase increases a little at x = 0.02 due to the slightly decreased T O–T .…”

“…Raman spectroscopy is an effective method to meticulously study the molecular symmetry. ,,, The effect of polarization on Raman scattering is a powerful method to evaluate the anisotropy, symmetry, molecular orientation, and configuration of crystals, by which the molecular structure could be determined by analyzing the variation of the phonon frequency and depolarization ratio . Therefore, unpolarized, cross (VH)-polarized, and parallel (VV)-polarized scattering geometries are applied to study the effect of Sb content on the crystal structure (Figure S4).…”

Progress on Emerging Ferroelectric Materials for Energy Harvesting, Storage and Conversion

“…So far, a general consensus is that there is no thickness limit on the existence of ferroelectricity, [53][54][55] and the polarization may decouple with lattice tetragonality in perovskites at ultrathin conditions. [56,57] At T > T C , polar nanoclusters and precursor dynamics prevail in perovskite ferroelectrics below a temperature of ≈T C + 75 K. [58,59] Among the FE oxides, it is noteworthy that materials like HfO 2 show an opposite thickness scaling behavior, whose FE property disappears above a critical thickness. [60] On the energy scale, to stabilize an FE state, a longrange electrostatic force should appear to compete with the short-range repulsive force, which usually favors a nonpolar symmetric structure.…”

A Predictive Theory for Domain Walls in Oxide Ferroelectrics Based on Interatomic Interactions and its Implications for Collective Material Properties

“…Schematic of the relationship between the simple 5-atom cell, domain walls and collective properties of ferroelectric perovskite oxides. The images in the bottom panel are taken from refs [40,43]…”

“…Copyright 2016, Springer Nature. Right-hand image: Reproduced under the terms of the CC-BY Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/ by/4.0) [43]. Copyright 2021, The Authors, published by Springer Nature.…”