查看更多>>摘要：The development of ABO_3 perovskite-structured dielectric materials with high recoverable energy storage density (V_(rec)) and power density (P_D) is crucial for the downsizing of pulsed power devices. Despite several research efforts, achieving a high W_(rec) over a wide working temperature range in an environmentally benign system remains a difficulty. A synergistic design strategy is given here, which includes concurrently doping at the A- and B-site to achieve a spread and depressed dielectric response, adding sintering aids, and employing advanced viscous polymer rolling technology for dense and ultra-thin ceramic samples, respectively. Finally, at a relatively low electric field of 380 kV/cm, an ultrahigh W_(rec) of 6.57 J/cm~3 is realized in (Bi_(0.5)Na_(0.5))_(0.93)Ca_(0.07)Ti_(0.85)Zr_(0.15)O_3-0.5 wt% Li_2CO_3 component, which benefits from gentle polarization saturating and improved breakdown strength. The W_(rec) can be maintained above 6 J/cm~3 while maintaining strong thermal stability (variation ≤ ± 3%) over a temperature range of 30-150 °C. Because BNT-based materials have such high energy storage performance and temperature stability, they are not only a promising candidate for replacing lead-based dielectrics, but also a valuable guide for developing new high-performance ferroelectric materials for future energy storage devices in the pulsed power system.
查看更多>>摘要：This study is focused on the synthesis condition influence related to structural and spectroscopic properties of the potassium strontium pyrophosphate (K_2SrP_2O_7) co-doped with Eu~(3+) and Eu~(2+) ions. The experimental parameters of the urea assisted combustion synthesis were optimized by temperature and time of calcination as well as reduction atmosphere composition. The obtained materials were structurally characterized using the X-Ray Powder Diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Spectroscopic properties were determined by emission spectra, excitation spectra, luminescence kinetics and luminescence temperature quenching measurements. It was found that increasing concentration of Eu~(3+) ions caused an increase of spectroscopic factors, which correspond to the relative integrated luminescence intensities of ~5D_0-~7F_∫ transitions as well as structural defects. Moreover, the successful Eu~(2+) ion incorporation was proven by optical spectroscopic measurements, which showed the allowed f-d transitions.
查看更多>>摘要：Yttrium doped ZnO nanorod array films are hydrothermaliy grown on fluorine doped tin oxide substrates. The yttrium doped ZnO samples maintain the same wurtzite crystal structure and nanorod morphology as those of the undoped samples, but they shows much enhanced photoelectrochemical water splitting performance. It is found that yttrium doping not only enhances the light absorption of the ZnO, but also provides more donors for ZnO and thereby enhances the conductivity of the ZnO nanorods. Moreover, the charge carrier lifetime of ZnO becomes longer after yttrium doping. These changes in the electronic structure of ZnO caused by yttrium doping significantly improve its photoelectrochemical performance. Under AM 1.5 G illumination at 100 mW/cm~2 and a potential of 1.23 V vs. reversible hydrogen electrode, the yttrium doped ZnO samples can get a photocurrent density of - 0.50 mA/cm~2, while the undoped ZnO samples only show photocurrent densities of ~ 0.30 mA/cm~2 under the same conditions. Considering that ZnO has advantages of low cost, environmental friendliness and simple and mild preparation process, it is expected that the yttrium doped ZnO nanorod array films will provide valuable platforms for a wide photocatalytic applications, not just limited to photoelectrochemical water splitting.
查看更多>>摘要：Lithium ion batteries (LIBs) based on solid state electrolytes have attracted much attention for their high safety and energy density. Li_(29)Zr_9Nb_3O_(40) powders as Li-ionic conductors were prepared using a sol-gel method in this work, and the related ceramics were sintered in air or in an oxygen-deficient atmosphere in which sample was covered with corundum crucible. All the sintered ceramics are consisted of orthorhombic phase. Li_(29)Zr_9Nb_3O_(40) ceramic sintered in oxygen-deficient atmosphere has conductivity of 1.03 × 10~(-3) S cm~(-1) at room temperature and has ionic transference number of 0.9996, while the ceramic sintered in air has conductivity of 4.41 × 10~(-5) S cm~(-1). The influence of oxygen vacancy on the migration path of Li-ion was discussed. The migration paths of Li-ions between two kinds of Li_(29)Zr_9Nb_3O_(40) ceramics were simulated and visualized by method of bond valence site energy with VESTA software.
查看更多>>摘要：The fabrication of 2:17-type Sm-Co-Fe-Cu-Zr magnets that have served as the strongest high-temperature permanent magnets for nearly half a century requires a strict processing control to form full cellular na-nostructure. Considering that slow cooling after solution-treatment may enable a more homogeneous temperature field inside the chamber and more slight magnetic properties difference among the magnets in mass production than rapid cooling, here we performed a comparative study on a model magnet Sm_(25)Co_(46.9)Fe_(19.5)Cu_(5.6)Zr_(3.0) (wt%) to investigate how the post-solutionizing cooling rate affects the micro-structure and magnetic properties. In comparison with the rapid cooling condition, slow cooling produces coarser cellular nanostructure and lower defects density at the solution-treated state. Such initial micro-structural difference leads to slower 1:5 H growth kinetics and slower defects dissociation kinetics during the subsequent aging process, characterized by the smaller fraction of 1:5 H cell boundary phase and the higher density of remanent defects in the slowly-cooled final magnets. Since the 1:5 H phase plays a dominant role on the coercivity and the remanent defects are harmful to hard magnetic properties, further work reveals that longer aging time can promote the formation of 1:5 H phase and to reduce the harmful defects for achieving better magnetic performance in the slowly-cooled magnets. These findings may be helpful for achieving uniform magnetic performance in mass production of 2:17-type Sm-Co-Fe-Cu-Zr magnets.
查看更多>>摘要：As a compelling complement to lithium batteries, rechargeable aluminum batteries (RABs) have attracted considerable attention because of abundant natural resources, high volumetric capacity, and safety property of aluminum metal. However, the deployment of RABs is hampered by the lack of favorable cathodes with high capacity and rapid kinetics. To address the long-unresolved issue of aluminum-storage capacity and rate, here we design a heterostructured g-C_3N4/Ti_3C_2T_x hybrid which offers a conductive supporting framework to maintain structural integrity and accelerate electronic transport. The energy storage mechanism of the heterostructured g-C_3N_4/Ti_3C_2T_x cathode was demonstrated as the reversible intercalation of AlCl_4~-during cycling. Moreover, the battery-capacitance model mechanism in the heterostructured g-C_3N_4/Ti_3C_2T_x hybrids may accelerate the kinetics of the electrode reactions. Furthermore, DFT calculations certify that heterostructured g-C_3N_4/Ti_3C_2T_x possesses enhanced electrical conductivity and Al trapping capability. Accordingly, the heterostructured g-C_3N_4/Ti_3C_2T_x cathode affords RABs with an excellent Al-storage property (237 mAh g~(-1) at 0.5 Ag~(-1)) and considerable rate capabilities (174 mAh g~(-1) at 4 A g~(-1)) among state-of-the-art cathode materials for aluminum batteries.
查看更多>>摘要：The chemical doping of carbon and heteroatoms is expected to be a promising strategy for enhancing the absorption properties of electromagnetic waves. In this work, N-doped C/ZnO composites (CN/ZnO_x-Ts) were originally designed and synthesized by using temperature-controllable calcination engineering with zinc-based acrylate resins containing N atoms as precursors. The best electromagnetic wave absorption (EMWA) performance for the composites was obtained by changing the composition and calcination temperature of the acrylate resin precursor. A CN/ZnO_(0.064)-900 composite prepared using a precursor containing acrylonitrile (0.4 mol) and ZnO (0.064 mol) calcined at 900 °C showed a minimum reflection loss (RL_(min)) of - 43.15 dB at 3.0 mm and 9.68 GHz, with an effective absorption bandwidth (EAB) ranging from 5.1 GHz to 18 GHz achieved by adjusting the thickness of the absorber. This method for preparing novel N-doped carbon-based materials provides the possibility for the mass production of highly efficient absorbers.
查看更多>>摘要：Na_(0.44)MnO_2 microrods with high crystallinity have been prepared by a simple solid-phase method and then coated with ln_2O_3 by precipitation method. 1 wt% ln_2O_3 coating could improve the sodium-storage capability of Na_(0.44)MnO_2 microrods significantly. The original Na_(0.44)MnO_2 microrods could provide the maximum discharge capacity of 100.3 mAh g~(-1) under a wide voltage of 2.0-4.5 V at 1 C, but the discharge capacity rapidly decreases to 70.4 mAh g~(-1) after 400 cycles, which was only 70.3% of the maximum capacity. However, the Na_(0.44)MnO_2 coated with 1 wt% In_2O_3 exhibited a high discharge capacity of 90.9 mAh g~(-1) after 400 cycles, with high-capacity retention of 86.7% in the same case. Moreover, compared with Na_(0.44)MnO_2, 1 wt% In_2O_3 coated Na_(0.44)MnO_2 shows better rate capability. Even at a high current density of 10 C, the discharge capacity is 63.6 mAh g~(-1), much larger than the 32.9 mAh g~(-1) of the pristine Na_(0.44)MnO_2. The mechanism of In_2O_3 coating improving the electrochemical performance of Na_(0.44)MnO_2 microrods was studied in detail.
查看更多>>摘要：In this paper, the mechanism on the nucleation of orientation-preferred Cu_6Sn_5 at different temperatures and solder compositions was investigated. Results suggest that affected by temperature and solder composition, the distribution of clusters in solder plays an important role in the formation of preferred orientation. Higher temperature, Ag element and an appropriate amount of Cu element are favorable for the nucleation of orientation-preferred Cu_6Sn_5. However, the increase of Cu-Sn clusters size with the increase of Cu addition will lead to the nucleation of Cu_6Sn_5 in liquid solder, which does not need to follow the rule of the minimal lattice mismatch between Cu_6Sn_5 and Cu substrate. Meanwhile, the addition of Cu and Ag is conducive to the increase of grain size. Besides, the difference in solder volume between the central and edge region results in the difference in grain orientation. Furthermore, a model is established to illustrate that how the reflow temperature, Cu and Ag content affect the nucleation of orientation-preferred Cu_6Sn_5 through affecting the cluster evolution. The results have significant meaning in understanding and controlling the formation of Cu_6Sn_5 preferred orientation and improving the reliability of solder joints.
查看更多>>摘要：A binder-free positive electrode material of 3D starfish-like Co_3O_4/Ni forest is fabricated via a novel and facile hydrothermal process followed by thermal treatment. The morphological studies clearly showed the construction of starfish-like micro-flowers of Co_3O_4 nanostructure forest densely covered on the entire Ni current collector. The 3D-Co_3O_4/Ni electrode displayed an areal capacity as high as 143.28 mC cm~(-2) at 0.5 mA cm~(-2) and higher stability of 88.4% after 5000 cycles. Moreover, the fabricated 3D-Co_3O_4/Ni||3D-Bi_2O_3/Ti supercapattery delivered a maximum areal capacitance of 24.73 mF cm~(-2), the energy density of 6.73 uWh cm~(-2) and power density of 5250 uW cm~(-2) with good cycling stability > 71% capacity retention after 5000 cycles. The higher electrochemical performance of the electrode is delivered due to the availability of abundant electrochemically active sites in the 3D starfish-like Co_3O_4 microflower, which facilitates a higher electrochemical reaction. The starfish-like forest architectures allow rapid ion diffusion, and the binder-free electrode reduces the contact resistance, which fasten the electron transport. These tolerable results prompt the as-prepared electrode with 3D starfish-like Co_3O_4 microflower morphology as an auspicious positive electrode material for electrochemical energy storage devices.
NSTL
Elsevier