Relaxation ferroelectric material having excellent physical properties, including EHV-k, high dielectric constant and electrical giant card effect, has wide application in sensors, actuators and a freezer. Presence of relaxor ferroelectrics disordered structure, it is now recognized Reasons leading to excellent performance. However, despite the sustained and in-depth study of 50 years, on a physical model relaxation ferroelectrics has been controversial, "Nature" magazine has reviews relaxation ferroelectrics as "hopeless confusion" ( "hopeless messes ", Nature 441, 941 (2006)). Origin structure excellent properties relaxor dielectric material is a ferroelectric material and is undoubtedly one of the major challenges in the field of physical aggregation thereof.
Professor Qing Wang Pennsylvania State University research group in conjunction with X-ray diffraction (XRD), infrared spectroscopy nanometers (AFM-IR), and electrical characterization of first-principles disclosed ferroelectric material relaxation properties of the polymer in the polymer originated hand sex. Related papers under the title "Chirality-induced relaxor properties in ferroelectric polymers" published in Nature Materials. The author is a professor of communications papers Pennsylvania State University Department of Materials Qing Wang, lead author for the United States Department of Materials Science at Pennsylvania State University doctoral Yang Liu. Other authors, including the US Department of Materials Pennsylvania State University Wenhan Xu, Aziguli Haibibu, Zhubing Han and North Carolina State University, Department of Physics, Bing Zhang, professor of Wenchang Lu and Jerry Bernholc.
Chiral (chirality), comes from the Greek word "hand" χειρ (kheir), represents an important asymmetry in the multi-domain multi-disciplinary. For example, if a mirror having an asymmetric carbon atom on the polymer molecular chains, will lead to polymers having a chiral. 2018, the research group Prof. Qing Wang vinylidene fluoride - trifluoroethylene copolymer P proof (VDF-TrFE) may change the regulation of the components are arranged so as to induce chiral form a quasi-phase boundary (the MPB), ferroelectric polymerization pressure record the electrical properties of improved nearly doubled (Nature 562, 96 (2018)). Professor Qing Wang team found that with increased with chiral TrFE monomer, cause P (VDF-TrFE) The transition to the ground state the helical conformation of a zigzag, the transition is accompanied by the emergence of new relaxor ferroelectric phase appears. That overcame awareness of relaxation ferroelectric polymers, because previous research believe that P (VDF-TrFE) is a ferroelectric phase, only induce relaxation ferroelectric polymer by electron or ion bombardment to phase ( Science 280, 2101 (1998)). On this basis, Qing Wang Prof. TF further disclosed relaxor ferroelectric polymer having a unique molecular structure disordered conformation, unlike inorganic perovskite relaxation (such as Pb (Mg1 / 3Nb2 / 3) O3-xPbTiO3) chemical components of the disorder. Research results show that chiral molecules is a critical factor leading to disordered conformation.
FIG. 1. a schematic monomers different polymers. B X-ray diffraction of different ferroelectric polymer component. c P (VDF-TrFE) 65/35 mol% copolymer variable temperature X-ray diffraction. FIG PTrFE energy at different chirality and different conformations d density functional theory calculations. E inner helical conformation swirl angle schematic distortion. f density functional theory PTrFE swirl angle helical conformation distortion energy within the lead correction. g force field simulation PTrFE helical configuration relative to the angle of rotation caused by the distortion energy correction.
The team by X-ray diffraction of the conventional relaxor ferroelectric polymer structure was characterized (FIG. 1), the summary found prior relaxor ferroelectric polymer PTrFE homopolymer having the same structure experimental law. On this basis, Qing Wang Professor team collaboration with Prof. Jerry Bernholc, first principle proved PTrFE homopolymer having a helical ground state, which is derived from a chiral unique arrangement. Helical conformation inherent distortion, resulting in disordered helical conformation of the molecule. The team is further proof of direct molecular conformation disorder resulting from the chiral (FIG. 2) nano-IR. Dielectric spectroscopy was confirmed and copolymers PTrFE relaxation (Figure 3). Meanwhile, according to this model, the team successfully discovered novel relaxor ferroelectric polymer material (FIG. 3).
Figure 2. Surface topography of A-C (1 × 1 μm2). D-E wave number 1288 cm-1 nano infrared spectrum. G-I Local infrared spectrum. a, d, g ferroelectric component of the copolymer P (VDF-TrFE) 80/20 mol%; b, e, h relaxor ferroelectric component of the copolymer P (VDF-TrFE) 45/55 mol%. c, f, i relaxor ferroelectric component copolymer P (TrFE).
Figure 3. Characterization medium temperature electrically spectrum: a PTrFE. b P (VDF-TrFE) 45/55 mol%. c PCTFE. d P (VDF-CTFE) 90/10 mol%.
In short, since the polymer material found since the relaxation properties of 20 years, with regard to its physical origins has been a lack of clear understanding, for relaxation ferroelectric polymer understand the physical model mostly inorganic perovskite ferroelectric materials borrowed relaxation, lack of appropriate structure basis. This study incorporated the chiral properties of the polymer, disordered conformation proposed physical model of chiral induction, explain the physical origin of the first polymer from the relaxation of the structure. This model not only help understanding Causes ferroelectric polymer excellent properties, such as large electrostrictive effect, the giant electrical card effect, high energy efficiency, the piezoelectric near the morphotropic phase boundary significantly enhanced the like, and several successful prediction new relaxor ferroelectric polymer material. These findings provide a new way to explore the molecular scale and design of high-performance relaxation ferroelectric materials.
Editor: pj, Read, original title: Nature Materials: chiral induction relaxation properties of ferroelectric polymer
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