High energy storage and ultrafast discharge in NaNbO3-based lead-free dielectric capacitors via a relaxor strategy

Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/3)O₃(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni_0·5Nb_0.5)O₃ boosts the insulation ability, thus obtaining a high breakdown strength (E_b) of 440 kV/cm in xBNN ceramics. A high energy storage density (W_total) of 4.09 J/cm³, recoverable energy storage density (W_rec) of 3.31 J/cm³, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of W_rec ≤ 0.4% over 5–100 Hz and W_rec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm³) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.     

离子色谱技术在钻井现场的应用研究

将离子色谱技术(IC)应用于钻井现场的钻井液滤液分析,从而获取所钻井钻遇地层的可溶性矿物的性质、地层水的类型等资料信息。离子色谱技术在这一领域的应用尚属探索阶段,但通过现场两口井的试用已见到较好的应用效果,文章简介了该技术的应用前景及价值,如:确定油水界面的位置及指导钻井液的调配、确保井下安全等。这方面的论述,对分析化验仪器向井场转移实现多手段综合分析具有一定的促进作用。     

模糊系统的微粒群并行聚类算法

为了解决大规模的数据聚类问题时需要的大量计算,提出了一种模糊系统的微粒群优化并行k-means聚类算法。该方法利用模糊规则,动态地调整微粒群惯性权重和加速因子,克服群体逐渐失去迁移性而停止进化的问题,保证群体多样性而避免陷入局部极小值。采用任务并行和部分异步通信模式,降低计算时间。实验结果表明,该算法在并行机群上运行时,加快了聚类算法的计算速度,提高了聚类质量。     

Effective strategy to realise excellent energy storage performances in lead-free barium titanate-based relaxor ferroelectric

High-performance capacitors, which possess a high energy storage density, large power density and fast charge/discharge rate, are in high demand in pulsed power systems. Although several studies have been conducted to obtain excellent energy storage performances, the scientific and feasible guidance is lacking on how to quickly and efficiently find a material system with high recoverable energy storage density (W_rec), large energy storage efficiency (η), and excellent thermal stability. Herein, a strategy is proposed to concurrently regulate the temperature corresponding to the maximum dielectric constant (T_m) to around room temperature and enhance the relaxor characteristic. To our satisfaction, excellent energy storage performances with a high W_rec of 3.05 J/cm³, large η of 95%, and wide temperature stability (20–180 °C) were achieved in 0.85BaTiO₃-0.15Bi(Mg₀₅Sn_0.5)O₃ (0.15BMS) ceramics. In addition, these ceramics also exhibited a large discharge energy density (W_dis = 0.74 J/cm³) and fast discharge time (t_0.9 = 105 ns) over a broad temperature range (20–180 °C), which confirms their significant application potential in the high-temperature field. These results indicate that this work can provide an effective guideline approach to attain high-performance capacitors for application in pulsed power capacitors.     

Ba5Li2W3O15: A New Li‐Containing Perovskite‐Type Microwave Ceramic with High Q and Low τf

A new Li‐containing microwave ceramic Ba₅Li₂W₃O₁₅ with hexagonal perovskite structure was prepared through a solid‐state ceramic route. Small amount of scheelite BaWO₄ appeared as a second phase during sintering. The Ba₅Li₂W₃O₁₅ could be well densified at 1120°C and exhibits good microwave dielectric properties with permittivity (ε_r) of 25.4, high Q × f value about 39 000 GHz, and low temperature coefficient of resonate frequency (τ_f) of 10 ppm/°C. The addition of BaCu(B₂O₅) can effectively lower the sintering temperature from 1120°C to 900°C and does not induce degradation of the microwave dielectric properties. These results indicate that the Ba₅Li₂W₃O₁₅ ceramic might be a promising candidate in microwave dielectric resonators.     

Preparation of Sb3Nb3O13 powders using molten salt method

The powders of pure cubic phase of Sb₃Nb₃O₁₃ were obtained using molten salt method at 1,100 °C with incubation time of 3 h. The formation of a kind of compound with hydroxyl restrains the volatilization and oxygenation of antimony oxides. The powder of cubic Sb₃Nb₃O₁₃ shows octahedral shape and its size lies between 1 μm and 20 μm. Densified ceramic was obtained using the Sb₃Nb₃O₁₃ powders. The microstructure of ceramic samples was studied by XRD and SEM analysis. And the dielectric properties as a function of frequency and temperature were measured between 25 °C and 550 °C and 100 Hz∼1 MHz.     

牛庄洼陷沙三下—沙四上泥页岩特征及沉积环境

为了明确非常规油气藏中不同泥页岩岩石类型与沉积环境的关系,针对不同泥页岩特征及沉积成因问题,通过岩心观察,利用岩矿薄片、扫描电镜、显微荧光以及元素分析等分析化验手段,开展了牛庄洼陷沙三下—沙四上泥页岩沉积环境分析及其与泥页岩岩相类型的对应关系研究.结果表明:牛庄洼陷沙三下—沙四上泥页岩共发育纹层状泥质灰岩、纹层状灰质泥...     

Thermally Stable BaTiO3-Bi(Mg0.75W0.25)O3 Solid Solutions: Sintering Characteristics,Phase Evolution,Raman Spectra,and Dielectric Properties

(1 ? x)BaTiO₃-xBi(Mg_0.75W_0.25)O₃ [(1 ? x)BT-xBMW, 0.02 ≤ x ≤ 0.24] ceramics were synthesized by a two-step solid-state reaction technique. X-ray diffraction (XRD) patterns show that a systematic structure evolution from tetragonal to pseudocubic phase was observed at x = 0.07. Raman spectra analysis illustrates that a change in average structure was observed with increasing x, and the local crystal symmetry which deviated from the idealized cubic perovskite structure appeared as x ≥ 0.07. Temperature dependence of dielectric properties indicates that the phase transition temperature (T _c) decreased with increasing x. Moreover, (1 ? x)BT-xBMW (0.07 ≤ x ≤ 0.24) ceramics show good dielectric thermal stability over a wide temperature range, which indicates that these ceramics are candidates for thermal stability devices.     

Significant effects of powder preparation processes on the physical properties of Bi0.5Na0.5TiO3–0.06BaTiO3 ceramic

(1?x)Bi_0.5Na_0.5TiO₃s (solid-state method)–xBi_0.5Na_0.5TiO₃g (sol–gel method)–0.06BaTiO₃ (0 ≤ x ≤ 1) ceramics were prepared and the effect of powder synthesis conditions on the physical properties of ceramics was investigated. A morphotropic phase boundary was observed in the Bi_0.5Na_0.5TiO₃–0.06BaTiO₃ system. With increasing Bi_0.5Na_0.5TiO_3g content, the maximum value of dielectric constant reduces sharply. The Bi_0.5Na_0.5TiO₃g significantly disrupts the long-range ferroelectric order dominant of the ceramics, which leads to a degradation of the remanent polarization and coercive field. These results may be helpful to further understand and design new Bi_0.5Na_0.5TiO₃-based lead-free piezoelectric ceramics.     

An approach to further improve piezoelectric and ferroelectric properties of (K0.5Na0.5)NbO3 ceramic

In this communication, an approach to further improve the electrical properties of (K_0.5Na_0.5)NbO₃ (KNN) ceramic (abbreviated as KNN₂) was reported. For the conventional ceramic technique (abbreviated as KNN₁), the raw materials of K₂CO₃, Na₂CO₃ and Nb₂O₅ were directly used without further processing, while those for KNN₂ were ball milled before mixing. The powders prepared by KNN₂ exhibited smaller and uniform. The ceramics have higher densities than that of KNN₁, which significantly improved the piezoelectric and ferroelectric properties of ceramics. The KNN₂ ceramics exhibited very good piezoelectric properties with d₃₃ = 123 pC/N, k_p = 33.8 %, Q_m = 219.8 and P _r  = 20.2 μC/cm³, indicating that KNN₂ is a strategy to obtain a dense KNN ceramic with more excellent electrical properties.