查看更多>>摘要：A Li_(0.27)K_(0.72)Ni_(0.6)Co_(0.2)Mn_(0.2)O_2 (LKNCM) cathode for potassium-ion batteries (PIBs) was obtained from LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 (NCM622) via ion exchange. In-situ X-ray diffraction and high-resolution transmission electron microscopy analyses showed the morphological and structural changes that occur during K~+-ion insertion. Particularly, the primary particles became porous, and the (003) interlayer distance expanded from 4.76 to 6.50 A, providing a potassiation/depotassiation framework. Inductively coupled plasma-optical emission spectroscopy revealed that 0.72 mol of K~+ ions were inserted into the Li-extracted NCM622 cathode per formula unit, indicating that the amounts of extracted Li~+ and inserted K~+ were similar. The developed LKNCM cathode exhibited a theoretical capacity of 160.79 mAh g~(-1) and an initial discharge capacity of 106.95 mAh g~(-1) with an average potential of 3.1 V vs. K/K~+. These results demonstrate that ion exchange enables layered NCM cathodes for lithium-ion batteries to be applied as cathodes for PIBs.
查看更多>>摘要：Luminescence thermometry (LT) is a remote technique of temperature monitoring, which shows immense potential and has become very popular among researchers in recent years. LT can be realized by several different measurement methods, but one of the most recently proposed and least studied relies on a single-band ratiometric (SBR) approach. In the SBR approach, the temperature readout is achieved from a single emission band being photoinduced by two different excitation conditions, i.e. ground (GSA) and excitated (ESA) state absorption. However, the intensity of emission resulting from ESA excitation is dependent on many factors such as host material properties, type and concentration of optically active dopant ions, surface effects, and others, so an in-depth understanding of photophysical processes is essential for the intentional development of novel highly sensitive luminescent thermometer operating on the SBR principle. In these studies, the impact of host and interionic interactions occurring through cross-relaxation on the thermometric properties of a single-band ratiometric thermometer based on nanosized NaYF_4 and NaGdF_4 fluorides doped with Eu~(3+) ions are investigated and discussed. The maximum relative temperature sensitivity was equal S_R= 16.9%/K at 163 K for the NaGdF_4:50%Eu~(3+) nanocrystals and was close to 1%/K over the entire higher temperature range analyzed.
查看更多>>摘要：The laser powder bed fusion (LPBF) was employed to process the ZK60 Mg alloy. The effect of heat treatment on the microstructure and hardness of LPBF ZK60 Mg alloy was investigated. The results showed that the grain boundary of LPBF ZK60 Mg alloy was composed of a network Mg_7Zn_3 phase. Three types of precipitated phases were distributed inside the grains: the type-I is Zn-rich precipitated phase with Zr-rich core, the type-II is Zn-rich precipitated phase without Zr, the type-Ill is Zr-rich particle. When the solution treatment was used, the Mg_7Zn_3 phase at the grain boundary melted and merged into the matrix. The precipitated phase in the grain mainly evolved into Zn-rich phase with Zn_2Zr core. Continue with the aging heat treatment, the rod-shaped pY-MgZn precipitated phase separated out from the a-Mg matrix. The length of the rod-shaped precipitated phase undergone double aging is longer and the quantity is more than that of the single aging. The rod-shaped β_1-MgZn precipitated phase significantly improved the mechanical properties of LPBF ZK60 Mg alloy. The average hardness increased from 0.88 ± 0.025 GPa to 1.01 ± 0.010 GPa and the ultimate tensile strength increased to 287 ± 4 MPa after the solution treatment plus double aging heat treatment.
查看更多>>摘要：Transition metal sulfides (TMSs) have been widely researched as promising electrode materials for super-capacitors because of their high theoretical capacitance and rich redox reactive sites. In this work, tremella-like core-shell Co_9S_8@NiCo_2S_4 heterogeneous nanosheets were directly grown on Nickel foamed (NF) through the hydrothermal+electrodeposition method to obtain a self-supporting electrode. Benefiting from its unique tremella-like structure, ultra-thin nanosheets, and the positive synergies between Co_9S_8 and NiCo_2S_4, the prepared Co_9S_8@NiCo_2S_4@NF electrode presents a high specific capacity of 513 C g~(-1) (specific capacitance -1026 F g~(-1)) at 1 A g~(-1) with superior rate capability (62.8% capacitance retention rate at 10 A g~(-1)). Furthermore, the fabricated Co_9S_8@NiCo_2S_4@NF//active carbon (AC) hybrid supercapacitor displays a high energy density of 30 Wh kg~(-1) at a power density of 731.8 W kg~(-1) and superior cycling stability. The results prove that the strategy of hydrothermal+electrodeposition is a very effective method for the preparation of energy storage and conversion materials with unique core-shell morphology.
查看更多>>摘要：The understanding of the fracture mechanism of amorphous alloys (AAs) is of importance for their engineering applications as advanced structural materials. In this study, a series of micro-tensions of Cu_(45)Zr_(45)Co_(10) AA microwires were conducted under different strain rates ranging from 5 x 10~(-5)s~(-1) to 1 x 10~(-2)s~(-1). It is found that all microwires fracture by shear cracking, but the shear fracture strengths exhibit pronounced rate-dependent uncertainties. Based on both lognormal and Weibull statistical analyses, the studied AA microwires reveal a positive rate-sensitivity of fracture strengths. However, increasing strain rates incurs the decrease in the fracture reliability. We demonstrate that the fracture reliability of AA microwires is dominated by a square root singularity of the characteristic lengths of shear offset on fracture surfaces, which satisfies linear elastic fracture mechanics.
查看更多>>摘要：A hybrid-material of titanium-oxide quantum dots (QDs) anchored on graphene nanoribbons (TiO_2@GNRs) was prepared by a simple hydrolysis strategy followed by heat-treatment. The GNRs can effectively accelerate the charge transference in the TiO_2@GNRs. And the TiO_2 QDs of ~5 nm can be thoroughly lithiatied/ sodiated in electrically confined space of GNRs. Motivated by its unique structure, the electrochemical charge/discharge behaviors of the TiO_2@GNRs serving as anodes for Li/Na-ion batteries (LIBs/SIBs) were evaluated. Reversible charge capacities of 320.8 mAh g~(-1) for LIBs and 101.6 mAh;g~(-1) for SIDs were demonstrated over 100 cycles at a rate of 0.5 A g~(-1), respectively. And Li and Na storage capacities of 209.0 and 42.2 mAh g~(-1) were retained at 8.0 A g~(-1) respectively. The desirable charge capacities, stable cyclic ability, and excellent rate performance of TiO_2@GNRs can be ascribed to the ultra-small TiO_2 size benefiting for full insertion/extraction of alkali ions and shortening their transfer pathway as well as enhanced electronic and ionic conductivity of the overall electrodes and interfacial confinement of GNRs for maintaining the electrode integrity.
查看更多>>摘要：A novel organic-inorganic hybrid compound based on iron fluoride, formulated as (H_2Piper)_4 [(FeF_6)_2FeF_5(H_20)(H_20)4] (Piper = Piperazine), C1, has been synthesized through hydrothermal method and characterized by X-ray single-crystal diffraction, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and dielectric measurements. Single-crystal X-ray study demonstrated that C1 crystallizes in P 1 space group with lattice parameters: a =12.5535(5) A, b =12.8715(4) A, c =22.2774(8) A, a = 92.321(3)°, p = 95.957 (3)°, y = 91.946(3)°, V = 3574.6 A~3 and Z= 4. In the molecular arrangement, [FeF_6]`(3-) and [FeF_5(H_20)]~(2-) anions are connected to [H_2Piper]~(2+) cations and free water molecules through hydrogen bonds (O-H-F and N-H--F) generating 3D network. Thermal analysis (DSC and TG) of C1 confirmed the presence of two phase transitions as well as the temperature of the decomposition of the hybrid material. The complex impedance of C1 was investigated in the temperature range 410-530 K and in the frequency range 200-2.106 Hz. Additionally, an electrical equivalent circuit was reported to explain the impedance results. The variation of the dc and ac conductivity corroborated two phase transitions of the title compound. Furthermore, the frequency dependence of alternative current (ac) conductivity was interpreted in terms of Jonscher's law. The alternative current (ac) electrical conduction in C1 material was accounted for in terms of two processes that can be assigned to the hopping transport mechanism (CBH and NSPT model). The temperature dependences of dielectric permittivity indicated a relaxation process and highlighted the good protonic conduction of this material.
查看更多>>摘要：Annealing at different temperatures was applied to a hot-rolled Ti-15Nb-5Zr-4Sn-1Fe (wt%) alloy to obtain α+β dual-phase structure with varying a phase fraction. The evolutions of a + p dual-phase structure, mechanical properties, and deformation mechanisms were systematically investigated. With increasing a phase from 5.5% to 33.7%, the stability of the retained p matrix was gradually enhanced and the p domain size was decreased. The deformation mechanisms changed from stress-induced p to a' martensitic transformation to stress-induced p to a" martensitic transformation, mechanical twinning of the p matrix, and finally dislocation slip accompanied with increasing a phase. Accordingly, Young's modulus decreased monotonously attributed to gradually suppressed athermal a phase, while the yield strength first decreased slightly owing to the change of stress-induced martensite from a' to a", and then increased rapidly when the long-range stress-induced martensite was suppressed. A good combination of low Young's modulus, high strength, and high ductility was obtained in a microstructure composed of ultrafine grained α+β dual-phase showing dislocation dominated plastic deformation. This study possibly serves as a templet to guide the development of ultrafine grained α+β dual-phase structured metastable p-Ti alloy for biomedical application.
查看更多>>摘要：The key to synthesis highly efficient MoS_2 based electrocatalyst for hydrogen evolution reaction (HER) is to construct a reasonable composite system structure to improve the stability, reduce the aggregation and improve the intrinsic poor conductivity. In this paper, M0S_2 composite of erbium-based metal-organic framework (noted as Er-MOF/MoS_2) were synthesized by hydrothermal method. The morphology and structure of the synthesized samples were characterized by powder X-ray diffraction (XRD), field emission electron microscopy (FESEM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), and the electrocatalytic performances were tested by linear sweep voltammograms (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), i-t. On the basis of the experiment, Er-MOF/M0S_2 shows improved conductivity and more exposed active sites, exhibiting excellent HER activity in acidic media, with only 234 mV overpotential to achieve 10 mA cm~(-2), and a Tafel slope of 54.3 mV dec~(-1). This strategy of porous structure of MoS_2 composite rare earth metal organic framework materials provides a novel and effective solution for preparing high performance MoS_2 based electrocatalyst.
查看更多>>摘要：Supercritical hydrothermal synthesis is a promising technology to produce nano-ZrO_2 due to its simple craft, short reaction time and low cost. In this paper, nano-ZrO_2 particles with an average particle size of 5.66-35.43 nm were successfully prepared by supercritical hydrothermal method. Meanwhile, the influences of reaction temperature, pressure, time, precursor concentration and pH value on the particle size distributions and surface topographies of nano-ZrO_2 were investigated under different conditions. Reaction time and precursor concentration were strong influencing factors of particle sizes and distributions. The reaction mechanisms of different crystal forms were controlled by pH value of the precursor. Under acidic conditions, soluble [Zr4(OH)_8(H_2O)_(16)]~(8+) was produced due to the hydrolysis of precursors, and the appearance of abundant monoclinic nucleus was triggered subsequent condensation of [Zr_4(OH)_8(H_2O)_(16)]~(8+). In-situ crystallization dominated the crystallization process and the tetragonal phase was formed by the rearrangement of the precursor structures. The intermediate product Zr(OH)_3NO_3 was detected under high pH conditions.
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Elsevier