Wenyuan Liu

Bio: Wenyuan Liu is an academic researcher from Xi'an Jiaotong University. The author has contributed to research in topics: Piezoresponse force microscopy & Materials science. The author has an hindex of 5, co-authored 6 publications receiving 68 citations.

Domain Engineered Lead-Free Ceramics with Large Energy Storage Density and Ultra-High Efficiency under Low Electric Fields.

Abstract: Dielectric energy storage materials are becoming increasingly popular due to their potential superiority, for example, excellent pulse performance as well as good fatigue resistance. Although numerous studies have focused on lead-free dielectric materials which possess outstanding energy storage characteristics, the results are still not satisfying in terms of achieving both large discharging energy density (Wd) and high discharging efficiency (η) under low electric fields, which is crucial to be conducted in miniatured electronic components. Here, we adopt the strategy of domain engineering to develop sodium bismuth titanate (Bi0.5Na0.5TiO3)-based ceramics employed in the low-field situation. Remarkably, a large Wd of 2.86 J/cm3 and an ultrahigh η of 90.3% are concurrently obtained in 0.94(Bi0.5Na0.5)0.65(Ba0.3Sr0.7)0.35TiO3-0.06 Bi(Zn2/3Nb1/3)O3 system when the electric field is as low as 180 kV/cm. Additionally, the ceramic shows brilliant thermal endurance (20-160 °C) and frequency stability (0.1-100 Hz) with high Wd (>1.48 J/cm3) together with an ultra-high η (>90%). What's more, the ceramic displays a fast charge-discharge time (t0.9 = 109.2 ns). The piezoresponse force microscopy (PFM) results reveal that the introduced Bi(Zn2/3Nb1/3)O3 disrupts the microdomains of (Bi0.5Na0.5)0.65(Ba0.3Sr0.7)0.35TiO3 ceramics and promotes the formation of nanodomains, leading to enhanced energy storage properties. The current work may arouse interest in developing low-field high-performing dielectric capacitors for energy storage application.

Investigation on the bar clamping position of a new type of precision cropping system with variable frequency vibration

Abstract: The purpose of this paper is to obtain the correct clamping position of the bar during the cropping process based on a new type of precision cropping system with variable-frequency vibration. The mathematical model is built by finite-element method and the simulation experiments were designed by means of an orthogonal method. The analytical results show that the diameter D of the bar exerts an influence on the ratio of the maximum tension stress to the maximum shear stress near the notch bottom remarkably. The influence of the length L2 of second-segment bar extending out the clamping die on it can be minimal. The reasonable geometrical parameters of the clamping bar for a segment of bar with definite length to diameter ratio are determined: the proportion of L1 to the diameter D of the bar is 0.3, and the proportion of L2 to D is 0.25. According to the special feature of the obtained cutting surface, a new measurement method is proposed and applied to assess the quality of the cross-section. The theoretical analysis and experiments prove that, by reasonably setting clamping position of the bar, high-quality cross-section can be obtained.

High-performance lead-free bulk ceramics for electrical energy storage applications: design strategies and challenges

Abstract: Compared with fuel cells and electrochemical capacitors, dielectric capacitors are regarded as promising devices to store electrical energy for pulsed power systems due to their fast charge/discharge rates and ultrahigh power density. Dielectric materials are core components of dielectric capacitors and directly determine their performance. Over the past decade, extensive efforts have been devoted to develop high-performance dielectric materials for electrical energy storage applications and great progress has been achieved. Here, we present an overview on the current state-of-the-art lead-free bulk ceramics for electrical energy storage applications, including SrTiO3, CaTiO3, BaTiO3, (Bi0.5Na0.5)TiO3, (K0.5Na0.5)NbO3, BiFeO3, AgNbO3 and NaNbO3-based ceramics. This review starts with a brief introduction of the research background, the development history and the basic fundamentals of dielectric materials for energy storage applications as well as the universal strategies to optimize their energy storage performance. Emphases are placed on the design strategies for each type of dielectric ceramic based on their special physical properties with a summary of their respective advantages and disadvantages. Challenges along with future prospects are presented at the end of this review. This review will not only accelerate the exploration of higher performance lead-free dielectric materials, but also provides a deeper understanding of the relationship among chemical composition, physical properties and energy storage performance.

Giant energy-storage density with ultrahigh efficiency in lead-free relaxors via high-entropy design

Abstract: Abstract Next-generation advanced high/pulsed power capacitors rely heavily on dielectric ceramics with high energy storage performance. However, thus far, the huge challenge of realizing ultrahigh recoverable energy storage density ( W rec ) accompanied by ultrahigh efficiency ( η ) still existed and has become a key bottleneck restricting the development of dielectric materials in cutting-edge energy storage applications. Here, we propose a high-entropy strategy to design “local polymorphic distortion” including rhombohedral-orthorhombic-tetragonal-cubic multiphase nanoclusters and random oxygen octahedral tilt, resulting in ultrasmall polar nanoregions, an enhanced breakdown electric field, and delayed polarization saturation. A giant W rec ~10.06 J cm −3 is realized in lead-free relaxor ferroelectrics, especially with an ultrahigh η ~90.8%, showing breakthrough progress in the comprehensive energy storage performance for lead-free bulk ceramics. This work opens up an effective avenue to design dielectric materials with ultrahigh comprehensive energy storage performance to meet the demanding requirements of advanced energy storage applications.

Composition and Structure Optimized BiFeO3 -SrTiO3 Lead-Free Ceramics with Ultrahigh Energy Storage Performance.

Abstract: Dielectric ceramic capacitors have attracted increasing attention as advanced pulsed power devices and modern electronic systems owing to their fast charge/discharge speed and high power density. However, it is challenging to meet the urgent needs of lead-free ceramics with superior energy storage performance in practical applications. Herein, a strategy for the composition and structural modification is proposed to overcome the current challenge. The lead-free ceramics composed of BiFeO3 -SrTiO3 are fabricated. A low hysteresis and high polarization can be achieved via composition optimization. The experimental results and finite element simulations indicate that the two-step sintering method significantly influences the decrease in the grain size and improvement in the breakdown strength (EBDS ). A high EBDS of ≈750 kV cm-1 accompanied by a large maximum polarization (≈40 µC cm-2 ) and negligible remanent polarization (<2 µC cm-2 ) contribute to the ultrahigh energy density and efficiency values of the order of 8.4 J cm-3 and ≈90%, respectively. Both energy density and efficiency exhibit excellent stability over the frequency range of 1-100 Hz and temperatures up to 120 °C, along with the superior power density of 280 MW cm-3 , making the studied BiFeO3 -SrTiO3 ceramics potentially useful for high-power energy storage applications.