Ultrahigh Energy Storage Density in Superparaelectric‐Like Hf0.2Zr0.8O2 Electrostatic Supercapacitors

Abstract Electrostatic capacitors attract great interest in energy storage fields due to their advantages of high power‐density, fast charge/discharge speed, and great reliability. Intensive efforts have been placed on the development of high‐energy‐density of capacitors. Herein, a novel supercapacitor with Hf0.2Zr0.8O2/xAl2O3/Hf0.2Zr0.8O2 (HAHx) is designed to improve the breakdown strength (Eb) through optimizing Al2O3 (AO) film thickness. Low‐temperature annealing is first proposed to enhance the polarization difference (Pm−Pr) due to the formation of dispersed polar nanoregions, which is called “superparaelectric‐like” similar to previous super‐paraelectric behavior of perovskite structures. As results, both large Eb and Pm−Pr values are obtained, leading to an ultrahigh energy storage density of 87.66 J cm−3 with a high efficiency of 68.6%, as well as a reliable endurance of 107 cycles. This work provides a feasible pathway to improve both the polarization difference and breakdown strength of HfO2‐based films by the combination of insulation insertion layer and low‐temperature annealing. The proposed strategy can contribute to the realization of high‐performance electrostatic supercapacitors with excellent microsystem compatibility

Greatly improved piezoelectricity and thermal stability of (Na, Sm) Co-doped CaBi2Nb2O9 ceramics

Calcium bismuth niobate (CaBi2Nb2O9) is regarded as one of the most potential high-temperature piezoelectric materials owing to its highest Curie point in bismuth layer-structured ferroelectrics. Nevertheless, low piezoelectric coefficient and low resistivity at high temperature considerably restrict its development as key electronic components. Herein, markedly improved piezoelectric properties and DC resistivity of CaBi2Nb2O9 ceramics through Na+ and Sm3+ co-doping are reported. The nominal compositions Ca1-2x(Na, Sm)xBi2Nb2O9 (x ​= ​0, 0.01, 0.025, and 0.05) ceramics have been prepared via the conventional solid state method. An optimum composition of Ca0.95(Na, Sm)0.025Bi2Nb2O9 is obtained, which possesses a high Curie point of ∼949 ​°C, a piezoelectric coefficient of ∼12.8 ​pC/N, and a DC electrical resistivity at 500 ​°C of ∼4 ​× ​107 ​Ω ​·cm. The improved d33 is probably ascribed to the reduction in domain size and the increase in domain wall density caused by the reduced grain size. More importantly, after annealing at 900 ​°C for 2 ​h, the piezoelectric coefficient still maintains about 90% of the initial d33 value, which displays a significant improvement compared to pure CaBi2Nb2O9 ceramic with only 44% of the initial d33 value. This work exhibits a feasible approach to simultaneously obtain high piezoelectric property and thermal stability in CaBi2Nb2O9 ceramics by Na+/Sm3+ co-doping

Terahertz reading of ferroelectric domain wall dielectric switching

“This document is the Accepted Manuscript version of a Published Work that appeared in final form in [ACS Applied Materials and Interfaces], copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/full/10.1021/acsami.1c00523Ferroelectric domain walls (DWs) are important nano scale interfaces between two domains. It is widely accepted that ferroelectric domain walls work idly at terahertz (THz) frequencies, consequently discouraging efforts to engineer the domain walls to create new applications that utilise THz radiation. However, the present work clearly demonstrates the activity of domain walls at THz frequencies in a lead free Aurivillius phase ferroelectric ceramic, Ca0.99Rb0.005Ce0.005Bi2Nb2O9, examined using THz time domain spectroscopy (THz-TDS). The dynamics of domain walls are different at kHz and THz frequencies. At low frequencies, domain walls work as a group to increase dielectric permittivity. At THz frequencies, the defective nature of domain walls serves to lower the overall dielectric permittivity. This is evidenced by higher dielectric permittivity in the THz band after poling, reflecting decreased domain wall density. An elastic vibrational model has also been used to verify that a single frustrated dipole in a domain wall represents a weaker contribution to the permittivity than its counterpart within a domain. The work represents a fundamental breakthrough in understanding dielectric contributions of domain walls at THz frequencies. It also demonstrates that THz probing can be used to read domain wall dielectric switching

Facile one-step synthesis and enhanced photocatalytic activity of WC/ferroelectric nanocomposite

The development of noble-metal-free co-catalysts is seen as a viable strategy for improving the performance of semiconductor photocatalysts. Although the photocatalytic efficiency of ferroelectrics is typically low, it can be enhanced through the incorporation of a co-catalyst into nanocomposites. Here, we demonstrate the influence of ferroelectricity on the decolorization of rhodamine B under simulated solar light using RbBi2Ti2NbO10 and compared the performance with that of non-ferroelectric RbBi2Nb5O16. The decolorization rate for RbBi2Ti2NbO10 was 5 times greater than that of RbBi2Nb5O16. This behaviour can be explained in terms of ferroelectric polarization, which drives the separation of charge carriers. The photocatalytic activity of RbBi2Ti2NbO10 was further enhanced to over 30 times upon preparing a nanocomposite with tungsten carbide (WC) through high energy ball milling. This enhancement was attributed not only to the increased specific surface area, but also to the incorporated WC co-catalyst, which also serves as a source of plasmonic hot electrons and extends the photocatalytic activity into the visible light range. The WC/RbBi2Ti2NbO10 nanocomposite shows interesting water oxidation properties and evolves O-2 with a rate of 68.5 mu mol h(-1) g(-1) and a quantum yield of 3% at 420 nm. This work demonstrates a simple route for preparing WC containing nano-ferroelectric composites for solar energy conversion applications

Facile one-step synthesis and enhanced photocatalytic activity of WC/ferroelectric nanocomposite

The development of noble-metal-free co-catalysts is seen as a viable strategy for improving the performance of semiconductor photocatalysts. Although the photocatalytic efficiency of ferroelectrics is typically low, it can be enhanced through incorporation of co-catalyst into nanocomposites. Here, we demonstrate the influence of ferroelectricity on the decolorization of Rhodamine B under simulated solar light using RbBi2Ti2NbO10 and compared the performance with nonferroelectric RbBi2Nb5O16. The decolorization rate for RbBi2Ti2NbO10 was 5 times greater than RbBi2Nb5O16. This behaviour can be explained in terms of ferroelectric polarization, which drives separation of the charge carriers. The photocatalytic activity of the RbBi2Ti2NbO10 was further enhanced to over 30 times upon preparing nanocomposite with tungsten carbide (WC) through high energy ball milling. This enhancement was not only attributed to the increased specific surface area, but also to the incorporated WC co-catalyst which also serves as source of plasmonic hot electrons and extends the photocatalytic activity into the visible light range. The WC/RbBi2Ti2NbO10 nanocomposite shows interesting water oxidation property and evolves O2 with a rate of 68.5 µmol h-1 g -1 and the quantum yield of 3% at 420 nm. This work demonstrates a simple route for preparing WC containing nano ferroelectric composites for solar energy conversion applications