Can the ferroelectric soft mode trigger an antiferromagnetic phase transition?

Type-II multiferroics, where spin interactions induce a ferroelectric polarization, are interesting for new device functionalities due to large magnetoelectric coupling. We report on a new type of multiferroicity in the quadruple-perovskite BiMn₃Cr₄O₁₂, where an antiferromagnetic phase is induced by the structural change at the ferroelectric phase transition. The displacive nature of the ferroelectric phase transition at 125 K, with a crossover to an order-disorder mechanism, is evidenced by a polar soft phonon in the THz range and a central mode. Dielectric and pyroelectric studies show that the ferroelectric critical temperature corresponds to the previously reported Néel temperature of the Cr³⁺ spins. An increase in ferroelectric polarization is observed below 48 K, coinciding with the Néel temperature of the Mn³⁺ spins. This increase in polarization is attributed to an enhanced magnetoelectric coupling, as no change in the crystal symmetry below 48 K is detected from infrared and Raman spectra.     

Recent progress on garnet-type oxide electrolytes for all-solid-state lithium-ion batteries

Currently, the safety of lithium-ion batteries has attracted much attention. All-solid-state batteries (ASSBs) are promising replacements for liquid-electrolyte lithium-ion batteries due to their high energy density and excellent safety. The choice of electrolyte is the most critical part of ASSBs. Li₇La₃Zr₂O₁₂ (LLZO)-based solid-state electrolytes (SSEs) render high energy density, wide electrochemical window and high lithium-ion mobility. However, their low lithium-ion conductivity compared with liquid organic electrolytes and rigid interfacial contact at electrode/electrolyte interface mainly hinder the development of LLZO-based ASSBs. Herein, we review recent progress in the area of LLZO-based SSEs by discussing the structure and transport mechanism of lithium (Li)-ions of LLZO. Also, we summarize bottleneck problems and corresponding solutions, providing theoretical basis and technical support for the development of LLZO-based ASSBs. Finally, future prospects of LLZO-based ASSBs are discussed in next-generation energy storage systems.     

Stress-dependent sintering behavior of porous thermal barrier coatings

Thermal barrier coatings (TBCs) are subjected to high temperature and complex stress fields during service in gas turbines. In this process, densification and hardening take place as the result of sintering, which is sensitive to boundary condition/external load. The stress-dependent sintering behaviors of porous TBCs were investigated in this work using a customized four-point bending method. Furthermore, stress-dependent sintering model was developed and implemented in finite element analysis to elucidate sintering mechanisms. It was found that stress gradient induced nonlinear differential sintering behavior, due to the accelerating and retarding effects of compressive and tensile stresses, respectively. In addition, microstructure-mechanical property relation was determined following the exponential law and high-throughput method was proposed for the characterization of stress dependence. The in-depth understanding of stress-dependent sintering behavior could provide guidance to the design and failure analysis of TBCs applied on complex shaped components in the hot section of gas turbines.     

隔振对象重量变化对准零刚度隔振器隔振性能的影响

本文主要研究隔振对象重量变化对一类准零刚度隔振器隔振性能的影响,并给出了新的研究结果.文中使用欧拉屈曲梁构建负刚度调节结构并设计了隔振系统的平衡位置可调机构.假设系统有轻微的过载和超载,推导了系统的动力学方程并进行求解,定义了非线性隔振系统的力传递率及位移传递率来评价系统的隔振性能.对线性隔振系统,超载会让隔振频率略微降低,共振放大峰略微增大.对于准零刚度隔振系统,力传递率和线性系统类似,但是对于位移传递率,过载会导致系统固有频率和共振放大峰均升高,反而不利于隔振.研究结果可以对此类隔振系统的使用场合以及对过载和轻载的选择有工程指导意义.     

模糊层次分析法在我国深空探测方案优选应用探究

中国深空探测是复杂的系统工程，涉及领域多、技术难度大、经费需求高，目前方案优选方法是论证组论证和中介机构专家评估后形成，该方法论证周期长，不易快速做出科学决策。本文基于模糊层次分析模型，考虑技术、科学、经费等多指标多层次结构，建立系统指标评价模型。以中国探月工程中嫦娥四号任务方案为具体算例，综合专家判断和理论分析，建立各层次指标的判断矩阵，计算权重系数，进而实现总体方案的优选应用评价。结果表明，技术、科学和经费这三个因素相对于周期和效益更为重要。在4个备选方案中，由长征四号丙发射中继星，长征三号乙发射着陆器和巡视器组合体的方案，排序权值最大，因此该方案为最优方案，这也与实际情况一致。本研究可为我国后续各类深空探测方案制定提供快速及科学的理论支撑。      

Fabrication of 4H-SiC piezoresistive pressure sensor for high temperature using an integrated femtosecond laser-assisted plasma etching method

The processing, particularly, etching of brittle, hard, and anti-corrosion materials represented by the third-generation wide bandgap semiconductor silicon carbide (SiC), is a significant challenge. Although SiC has excellent electrical, mechanical, and chemical properties, the difficulty of processing limits its application in various sensor devices. To solve this problem, in this study, an integrated processing method of femtosecond laser-assisted SiC dry etching is proposed, which realizes high surface quality and high rate etching of the SiC microstructure. Specifically, the effects of different laser processing parameters on the processing effect were first studied through orthogonal experiments. Experiments indicate that compared with laser power and laser scan times, laser processing speed has a more obvious impact on the processing effect. Subsequently, considering the elastic modulus anisotropy of SiC, a 5 MPa piezoresistive pressure sensor chip was designed. Using the proposed composite processing method, a chip sensitive diaphragm was obtained. The diaphragm thickness and diameter are 76 μm and 1700 μm respectively. The overall sensor chip dimension was 4000 μm × 4000 μm × 350 μm. Static tests demonstrated that the sensor have excellent performance with sensitivity of 6.8 mV/MPa, linearity of 0.69% FS, and repeatability of 0.078% FS. In addition, by designing high-temperature packaging, the sensor achieved a pressure test at 400 °C. This study verifies the feasibility of the composite processing method, realizes the fabrication and measurement of high-temperature pressure sensors, and provides a reference for the micro-and nanostructure processing of various SiC sensors.     

Solvothermally grown WO3·H2O film and annealed WO3 film for wide-spectrum tunable electrochromic applications

Tungsten trioxide (WO₃) is a classical electrochromic (EC) material with advantages of abundant reserves, high coloration efficiency and cyclic stability. However, WO₃ films are often accompanied by a narrow spectrum of modulation due to a single-color change from transparent to blue. In this work, we report a wide-spectrum tunable WO₃·H₂O nanosheets EC film solvothermally grown on fluorine-doped tin oxide (FTO) glass. Interestingly, the crystalline WO₃·H₂O nanosheets film is transformed into amorphous WO₃ after annealing at 250 °C for 1 h. The amorphous film can be transformed into crystalline WO₃ film by increasing the annealing temperature to 450 °C. After annealing at 250 °C, the WO₃ film exhibits an optical modulation of 75.8% in a broad solar spectrum range of 380–1400 nm and blocks 88.9% of solar irradiance. Fast switching responses of 4.9 s for coloration and 6.0 s for bleaching, and a coloration efficiency of 86.4 cm² C⁻¹ are also achieved. Additionally, the WO₃ film annealed at 250 °C also demonstrates an excellent cyclic stability, where 99.6% of the initial optical modulation can be retained after 1500 cycles. This simple and mild solvothermal method used in this work provides a new idea for the preparation of wide-spectrum tunable WO₃ EC films.     

Preparing EBCO superconducting targets with uniform phase structure by pressure slip casting

The grain size and phase structure uniformity of europium barium copper oxide (EBCO) superconducting targets would affect the superconducting properties of sputtered film. A uniformly dispersed EBCO slurry was used to prepare high-density green EBCO compacts using slip casting. The effects of milling time and slurry pH on EBCO slurries were studied. Based on the shrinkage data of the EBCO superconducting targets, the densification process was estimated and the apparent activation energy was calculated. The effects of the sintering process on the microstructure and phase composition of EBCO superconducting targets were investigated using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). When the sintering temperature was 950–1050 °C, the EBCO superconducting target comprised EuBa₂Cu₃O₇ and CuO, where a new phase Eu₂BaCuO₅ formed at a sintering temperature of 1100 °C. The Tc and ΔT of the EBCO superconducting target sintered at 950 °C for 30 h were 91.18 K and 2.35 K.     

轮腿式机器人轮-腿高效移动策略优化

复杂地形下的高效移动策略是轮腿式机器人研制过程中的技术难点。本文在常规移动策略的基础上，通过引入关节空间状态量描述支腿相对于机身的位姿，引入位姿转换量描述相邻时序的位姿状态量间的运动过程，进而建立起移动策略与时间和能耗的数学模型，并以移动时间最短和能耗最低为目标，建立了移动策略的优化模型，通过优化迭代形成轮-腿高效移动策略。复杂地形下的越障仿真表明，机器人采用轮-腿高效移动策略可实现越障功能，与常规移动策略相比，移动时间及能耗均明显降低，验证了轮-腿高效移动策略的有效性。     

Effect of microstructure on the performance of Zr6Ta2O17 ceramics as thermal barrier coatings

In this study, Zr₆Ta₂O₁₇ ceramics with porous, fine-grained, and coarse-grained structures were obtained via in situ solid-state reactions, and their mechanical characteristics were examined. The significantly low thermal conductivity of dense Zr₆Ta₂O₁₇ ceramics (1.0 W m⁻¹ K⁻¹) was due to the grain boundary gap caused by superstructured grains. A calcium–magnesium–alumina–silicate (CMAS) corrosion experiment demonstrated that the formation of an interlocking structure composed of ZrO₂, CaTa₂O₆, and ZrSiO₄ prevented the penetration of CMAS impurities, thereby revealing the application potential of porous ceramics. In dense Zr₆Ta₂O₁₇ ceramics, the low-volume diffusion induced by an entropy-stable structure is conducive for corrosion resistance; however, the grain boundary is vulnerable to attacks by CMAS, which can be mitigated by the formation of a coarse crystal structure, thereby effectively improving the corrosion performance. This work provides a critical perspective on the thermal barrier coating design of A₆B₂O₁₇ (A = Zr, Hf; BNb, Ta) ceramics.