Achieving high energy storage performance of Pb(Lu1/2Nb1/2)O3 antiferroelectric ceramics via equivalent A-site engineering

Manipulating the critical switching field between antiferroelectric (AFE) state and ferroelectric (FE) is an important concept for tuning the energy storage performance of AFEs. As one of the lead-based AFE systems, Pb(Lu_1/2Nb_1/2)O₃ promises high potential in the miniaturization of pulsed power capacitors, but the extremely high critical switching field and low induced saturated polarization demonstrate severe drawbacks with respect to temperature stability and flexibility. Here, A-site Ba²⁺ doping engineering is used to effectively reduce the critical switching field and improve the saturated polarization in Ba_xPb_1-x(Lu_1/2Nb_1/2)O₃ (0.01 ≤ x ≤ 0.08, abbreviated as xBa-PLN) ceramics. We found the AFE-FE phase transition can be occurred at 80ºC with a high energy storage density of 4.03 J/cm³ for Ba_0.06Pb_0.94(Lu_1/2Nb_1/2)O₃ ceramic. Our results show that Ba²⁺ additions destroy the antiparallel structure of AFE phase, and finally reduce the critical switching field, demonstrating a potential alternative to modulate the energy storage performance of AFEs.     

High-strength Ti2AlN ceramics prepared by pulse electric current sintering based on powders synthesized by molten salt method

Ti₂AlN powders were synthesized through molten salt method and re-calcination process using TiH₂, Al and TiN powders as raw materials at 1100 ℃. The composition of final composite was directly influenced by the initial Al and TiH₂ content in the starting mixture. The purity of the synthesized Ti₂AlN powder could reach 97.1 wt% when the Al molar ratio was 1.05. Then high strength Ti₂AlN ceramics were successfully prepared in different modes, including two forms of pulse electric current sintering (PECS/SPS) and hot-pressing sintering (HP). A record-high flexural strength of 719 MPa was obtained for the PECS/SPS with an electrical insulating die (PECS/SPS II) sintered sample, based on the synthesized powder in which the initial molar ratio of Al was 1.1. The sintering behaviors in various modes were analyzed, confirming the shrinkage of particles starting at lower temperature in PECS/SPS II. The density, microstructure, Vickers hardness and elastic modulus of sintered ceramics were also investigated. Therefore, the present work provided the new methods about powder preparation and ceramic sintering of Ti₂AlN, making it possible to be used as high strength structural ceramics.     

Relaxor antiferroelectric-like characteristic boosting enhanced energy storage performance in eco-friendly (Bi0.5Na0.5)TiO3-based ceramics

Ideal relaxor antiferroelectrics (RAFEs) have high field-induced polarization, low remnant polarization and very slim hysteresis, which can generate high recoverable energy storage W_rec and high energy storage efficiency η, thus attracting much attention for energy storage applications. True RAFEs, on the other hand, are extremely rare, and the majority of them contain environmentally hazardous lead. In this work, we use a viscous polymer rolling process to synthesize a novel and eco-friendly 0.65Bi_0.5Na_0.4K_0.1TiO₃-0.35[2/3SrTiO₃-1/3Bi(Mg_2/3Nb_1/3)O₃] (BNKT-ST-BMN) dielectric material, which possesses a very typical RAFE-like characteristic. As a result, this material has a high W_rec of 4.43 J/cm³ and a η of 86% at an electric felid of 290 kV/cm, as well as a high thermal stability of W_rec (>3 J/cm³) over a wide range of 30–140 °C at 250 kV/cm. Our findings suggest that the BNKT-ST-BMN material could be a potential candidate for use in energy storage pulse capacitors.     

Two step sintering of a novel calcium magnesium silicate bioceramic: Sintering parameters and mechanical characterization

Two-step sintering (TSS) was applied to control the grain growth during sintering of a novel calcium magnesium silicate (Ca₃MgSi₂O₈ – Merwinite) bioceramic. Sol–gel derived nanopowders with the mean particle size of about 90 nm were sintered under different TSS regimes to investigate the effect of sintering parameters on densification behavior and grain growth suppression. Results showed that sintering of merwinite nanopowder under optimum TSS condition (T₁ = 1300 °C, T₂ = 1250 °C) yielded fully dense bodies with finest microstructure. Merwinite compacts held at T₂ = 1250 °C for 20 h had the average grain size of 633 nm while the relative density of about 98% was achieved. Mechanical testing was performed to investigate the effect of grain growth suppression on the hardness and fracture toughness. Comparison of mechanical data for samples sintered under two sintering regimes, including TSS and normal sintering (NS), showed TSS process resulted in significant enhancement of fracture toughness from 1.77 to 2.68 MPa m^1/2.     

Coons' surface method for formulation of finite element of plates and shells

In this paper, we apply the Coons' surface method and fitted function interpolation to fit boundary conditions of the finite element, and obtain different displacement functions of the plate and shell rectangular element, as well as the sectorial element, parallelogram element, ring element and quadrilateral element. The method is easily implemented and its geometric significance and mechanical conception are quite clear. Both computing technique and operational procedure are relatively unified. It is convenient to formulate conforming elements and high-precision elements, and also may be applied to formulate mixed and hybrid elements.     

Optimization of II–VI based heterojunctions

The performance of heterojunction devices can be optimized by proper choice of characteristics of the two semiconductors forming the junction and by proper design. One very important element in design is the termination of the active volume of the device with surfaces of low, preferably zero surface recombination velocity. This paper discusses the rules governing the choice of ratios of energy gaps, electron affinities, doping levels, minority carrier lifetimes, lattice constants, etc. for the semiconductors comprising the pair. It also discusses the use of heterostructures to produce the low surface recombination velocity surfaces bounding the active volume of the device. The paper reviews principles of materials science which govern the choice of semiconductors for both the active regions of the device and the heterostructure “encapsulants”. The few attempts to realize electronic structures having the properties required by optimization theory will be described.     

New quasi one-dimensional AxNb6X8 phases isostructural with Nb3Te4

A large number of new ternary niobium chalcogenides A_xNb₆X₈ with A = Na,K,Rb,Ca,Cu,Ag,In,Zn,Cd,Sn,Pb and Bi, X = S,Te and A = Sn,Pb and Bi, for X = Se have been synthesized by molten salt ion exchange and/or ternary element insertion. TlNb₆X₈ with X = S,Te were prepared for the first time by high temperature methods. The A cations are incorporated into large empty channels of the three-dimensional network structure of Nb₃X₄. The volume of the crystal lattice is nearly independent of the size of the cations. The extent of insertion (the value of x) appears to be limited primarily by electronic effects.     

短波红外传感器的信噪比计算

在焦平面层,信噪比是设计中一项重要的指标．本文介绍了用等效电子数计算信噪比的方法,分析了其理论基础,并对其进行了讨论．     

碲镉汞红外探测器的前沿技术综述

红外光电探测器件在军事、民用和科学研究方面具有非常重要的应用。而碲镉汞(HgCdTe)由于自身的诸多优点在红外光电探测器的发展中起到了至关重要的作用,至今仍然是重要的战略战术应用中首选的材料体系。首先分析了针对新一代红外探测器所提出的SWaP3(Size,Weight,and Power,Performance and Price)概念,然后简略介绍了第三代红外焦平面研究背景下HgCdTe薄膜的衬底水平与材料生长情况,最后总结了大规模阵列器件、甚长波红外器件、高工作温度(High Operating Temperature,HOT)器件、超光谱探测器件、双色器件以及雪崩光电器件等前沿技术方面的研究进展。     

高精度圆感应同步器高速数据处理电路研究

圆感应同步器是一种精密的角位置传感器,其高精度高速数据处理电路意义重大。本文分析比较了圆感应同步器不同的激磁方式及输出检测方式,介绍了绝对角度测量原理、IRDC芯片及绝对式感应同步器角度测量电路的误差来源,最后给出了初步的研究结论。