查看更多>>摘要：TiAl alloys have been studied widely as promising candidates for high-temperature applications, while the application has been hindered due to the lack of room temperature ductility. Herein, we systematically investigated the effect of tensile loading direction and additional elements (Cr and Nb) on the initial deformation mechanism in the γ phase of TiAl alloys, which is one of the crucial factors to decide room temperature ductility. First, we carefully chose two different TiAl alloys with limited and enhanced ductility. Second, by synthesizing the sample with a single γ phase via extracting the composition of γ phase in both TiAl alloy composed of γ and α2 phases, the initial deformation mechanism of γ phase is confirmed depending on alloy composition as well as loading direction using an in situ transmission electron microscopy. Third, using the first principle density functional theory calculation, we carefully calculate the change in activation factors of deformation mechanism according to each additional element (Cr and Nb) in TiAl alloy. As a result, it can be understood that the deformation mechanism of the γ phase in TiAl alloys changes depending on the additional element as well as loading direction. In particular, by comparing the experimental and theoretical study, it was revealed that the activation difference of three deformation mechanisms in the γ phase of TiAl alloy decreases as Nb is added, which leads to the activation of all deformation mechanisms in the γ phase during deformation, and hence obtains the enhanced room temperature ductility in TiAl alloys. Our results provide an effective strategy for enhancing room temperature ductility of TiAl alloys via reduction of activation difference of deformation mechanisms in γ phase of TiAl alloys, which will open a new era to develop TiAl alloys with enhanced ductility for various structural parts in automotive and aerospace industries.
查看更多>>摘要：Glass-ceramics xZrO2?10Fe2O3?(90-x)V2O5 with ‘x’ between 0 and 30 mol% and yZrO2?(20-y)CaO?10Fe2O3?70 V2O5 glass with ‘y’ between 0 and 20 mol%, respectively abbreviated as xZFV and yZCFV, before and after heat treatment at 500 °C for 100 min, were evaluated as potential cathode-active materials for sodium-ion batteries (SIBs). Relationships between physical properties and local structure of xZFV and yZCFV glass-ceramics were investigated by 57Fe-M?ssbauer spectroscopy, V K-edge X-ray absorption near edge structure (XANES), X-ray diffractometry (XRD), DC four-probe method and differential thermal analysis (DTA). SIBs containing heat-treated xZFV glass-ceramics showed the highest discharge capacity of 153 mA h g?1 under a current density of 50 mA?g?1, which exhibited a high electrical conductivity of 1.8 × 10?2 Scm?1. Precipitation of V0.05Zr0.95O2 and Fe2V4O13 nanoparticles were confirmed from the XRD pattern of the heat-treated 20ZFV glass, consistent with the lower energy of the pre-edge peak at 5467 eV in the V K-edge XANES spectrum. This result is associated with the reduction of vanadium ions from VV to VIV. It is concluded that the precipitation of stable vanadium bronze phases with high electrical conductivity and structural stability effectively enable the high SIB capacity of these materials.
查看更多>>摘要：Lithium-rich manganese layered oxide (LLMO) materials are one of the key materials for high energy density lithium ion batteries, but the loss of lattice oxygen during cycling leads to the increase of lithium ion transport resistance and the deterioration of material properties. In this study, density functional theory is used to calculate the formation energies and doping sites of 13 rare earth-doped LLMOs. Rare earth elements tend to occupy the Co site in the LiMO2 phase and screen out Yb, Lu, etc. as the higher-order dopant. The theoretical screening is verified by synthesizing Li1.2Ni0.133Co0.123Mn0.533RE0.01O2 (RE= La, Ce, Nd, Eu, Tm, Yb and Lu) cathode materials. Compared with undoped materials, the doping effect of heavy rare earth elements is better than that of light rare earth elements, which is consistent with the calculation results. Among them, Yb doping has the lowest formation energy, which enhances the TM-O hybridization. The evolution of lattice oxygen is significantly reduced and the material exhibits excellent electrochemical performance (the first discharge capacity is as high as 342.5 mAh g?1). These results provide a reference for the preparation of rare earth doped lithium-rich layered cathode materials with high capacity and stability.
查看更多>>摘要：Pertaining to research on energy consumption and energy storage systems, new and efficient mixed metal oxides of NiCo2O4/CeO2 as pseudo-capacitor materials have been successfully prepared by sol-gel combustion method. The synthesized unique spinel nanomaterials have been analyzed for structural and morphological characterization by FT-IR, XRD, XPS and electron microscopy techniques. The mesoporous structure and large specific surface area of the synthesized nanomaterials provide an easy channel for ion mobility rendering an effortless redox process at the electrode/electrolyte interface. As a consequence, it is observed that NiCo2O4 mixed with 10% of CeO2 exhibits an excellent specific capacitance of 1355 Fg?1 at 5 Ag?1 along with a high cycling stability with only 4.7% capacity loss at the end of 6000 cycles at a charge-discharge current density of 10 Ag?1. The results obtained are in par with some of the recent electrode materials used for supercapacitors suggesting the possible employment of NiCo2O4/CeO2 mixed metal oxides in energy storage applications.
查看更多>>摘要：Magnesium based solid hydrogen storage material (MgH2) has the advantages of good safety and high hydrogen storage capacity in the shipping field. However, the high hydrogen absorption and desorption temperature have not been well solved. Herein, this work proves that it is very effective to improve the hydrogen storage performance of MgH2 by doping nano NiO/C catalyst. Specifically, experimental results showed that MgH2 + 9 wt% NiO/C composite could dehydrogenate at 195 °C, which was 155 °C lower than pure MgH2. In addition, 6.21 wt% H2 could be released rapidly at 300 °C for 10 min. After complete dehydrogenation, the absorption rate of hydrogen is 50 °C, which is 80 °C lower than that of pure MgH2. Moreover, 5.13 wt% H2 could be absorbed within 1 h at 125 °C and 3 MPa hydrogen pressure. In addition, dehydrogenation and hydrogen absorption apparent activation energies of MgH2 + 9 wt% NiO/C composite are 70.26 kJ/mol and 25.55 kJ/mol lower than those of pure MgH2, respectively. The cycle experiment showed that MgH2 + 9 wt% NiO/C had excellent cycle stability and could maintain 98.8% hydrogen storage capacity after 20 cycles. Furthermore, the study of the catalytic mechanism indicated that NiO/C catalyst is evenly distributed on the surface of MgH2. More importantly, Mg2Ni/Mg2NiH4 is generated in situ, which acts as a “hydrogen pump” and speeds up hydrogen diffusion during the hydrogen absorption and desorption cycle.
查看更多>>摘要：The present work reports the sol-gel-driven phase-dependent structural, optical, and electrochemical properties for monoclinic and hexagonal bismuth phosphate (BiPO4) nanostructures. The crystal structure symmetry distinction between the monoclinic and hexagonal BiPO4 phases was revealed by XRD, FTIR, and Raman spectroscopy. The XRD with Rietveld analysis infers the phase purity in the prepared samples. FESEM images showed the variation in diameter of the nanoplatelets as the temperature is increased. High-Resolution Transmission Electron Microscopy (HRTEM) provided accurate information on the morphology and size of the synthesized materials. The Selected area electron diffraction (SAED) pattern was used to understand the crystallinity of the samples. High-resolution TEM images allow us to see lattice planes, and calculation of lattice spacing was performed. Oxidation states and the composition of various elements in the material were confirmed by X-Ray Photoelectron Spectroscopy (XPS) spectra. The phase transformation from hexagonal and monoclinic BiPO4 structure is associated with the reaction medium of water-based interatomic distance and bond angle calculation. BiPO4 electrode having hexagonal phase demonstrates the excellent electrochemical evolution with improved specific capacity (~400.80 Fg?1) and longevity (~91.5% over 1100 cycles), respectively. The results analysis showed that morphology and Phase transition play a significant role in tuning the electrochemical performance of BiPO4 electrode, which implies that it could be a potential applicant for energy storage applications.
查看更多>>摘要：CsPbBr3 is considered as a promising photocatalyst owning to its excellent photoelectronic characteristics. However, the photocatalytic activity is still unsatisfactory due to its narrow light absorption range, weak electron reduction potential, and poor water-resistance. In this work, a three-dimensional porous melamine foam (MF) supported CsPbBr3?xIx was prepared via facile anti-solvent (isopropanol, IPA) and ion doping strategies, which successfully realize efficient photocatalytic CO2 reduction under liquid-phase H2O medium. The anti-solvent strategy enables uniform distribution of perovskite crystals on MF surface, which is beneficial to the increase of specific surface area and active sites. The iodine ion (I-) replacement can enhance light absorption and electron reduction capacity of CsPbBr3, contributing to the CO2 photoreduction. Under simulated solar irradiation, powdery CsPbBr3 exhibits no photocatalytic activity owing to its quick degradation in H2O medium. Interestingly, MF assisted perovskites presents the enhanced performance, with 195.97 μmol g?1·h?1 of product yield for CsPbBr2I (IPA), which is 22.0 times higher than that of MF/CsPbBr3. Moreover, the excellent photothermal recoverable effect and surface hydrophobicity of MF/CsPbBr2I (IPA) result in a long-period and stable photocatalytic CO2 reduction with no evident decrease of photocatalytic activity during 42 h.
查看更多>>摘要：Electrodeposition is a useful technique for preparing Bi2Te3 thin film based thermoelectric generators as power sources for wireless sensors because of its many advantages, including low cost, non-vacuum operation, and compatibility with microfabrication processes. However, electrodeposition of thin films on insulating substrates is challenging; moreover, electrodeposited films exhibit inferior thermoelectric properties. Herein, we report electrodeposition of Bi2Te3 thin films on an insulating substrate by incorporating a sputtering step. The thermoelectric properties of the films were improved by performing post-thermal annealing. A 0.5 μm-thick Bi2Te3 layer was sputter-coated on an alumina substrate; subsequently, Bi2Te3 films of different thicknesses (0.5–3.8 μm) were formed by varying the electrodeposition time (10–60 min). The films were oriented along the a,b-axis direction, while the crystallite size remained constant as the electrodeposition time increased. The thermoelectric properties of the films were evaluated at approximately 300 K in both in- and cross-plane directions. Maximum power factors, 11.0 and 13.9 μW/(cm·K2) in the in-plane and cross-plane directions, respectively, were observed at 60 min electrodeposition due to increased electrical conductivity. The dimensionless figure of merit in both plane directions was maximum (0.27) at 10 min electrodeposition because of low thermal conductivity (0.86 W/(m·K)).
查看更多>>摘要：Magnetoelectric (ME) and anelastic properties of two-layer ceramic composites based on Mn0.4Zn0.6Fe2O4 magnetostrictor and PbZr0.53Ti0.47O3 piezoelectric at DC magnetic field strengths of 0–220 Oe, temperatures of 293–393 K, and volume fractions of PbZr0.53Ti0.47O3 of 0.40–0.67 were studied. It was found that a converse ME coupling coefficient α31 increases with the DC magnetic field strength Н1, passes through a maximum with the volume fraction ν, and decreases as temperature T rises. Dependences of α31 on Н1, ν, and T are explained using a model of effective parameters of a heterogeneous medium. The inverse correlation is revealed between α31 and an internal friction at resonant frequencies. Dependences of the internal friction on Н1, ν, and T are associated with the interaction of ferroelectric domain boundaries with crystal-lattice defects.
查看更多>>摘要：This study focused on the production of [Cu–10 Ni]x–x wt% Si3N4 (x = 0, 3, 6, 9 and 12 wt%) nanocomposites through mechanical alloying followed by spark plasma sintering. An exhaustive exploration was carried out on the synthesised nanocrystalline/nanocomposite particles and sintered samples to study their structural characterisation and microstructural changes after 20 h of MA. The mechanical behaviour in terms of the compression test was carried out and correlated with the microstructural evaluations. The results indicated that the incorporation of Si3N4 nanoparticles decreased the matrix powder particle size considerably owing to the domination of fracturing mechanism. The results also showed that a higher strain hardening rate followed by the breaking up of the matrix powder particles occurred in the nanocomposite powders. The powder morphology of the nanocrystalline [Cu–10Ni] matrix ensured the uniform distribution of Si3N4 nanoparticles within it leading to the formation of dislocations in commensurate with the reinforcement addition. The sintered samples exhibited improved compression strength owing to the embedment of Si3N4 nanoparticles, strong bonding between the Si3N4 particles and the matrix, engendered dislocations and grain refinement. The ductility was examined and the strengthening mechanisms were computed for the deformed specimens. The results explained that the grain size, dislocation, and Orowan strengthening contributed more to the total strength and influenced the properties compared to other strengthening mechanisms.
NSTL
Elsevier