查看更多>>摘要：Colloids consisting of the CoCrCuFeNi high-entropy alloy nanoparticles in ionic liquid with the l-butyl-3-methylimidazolium ([BMIM]~+) cation and the tetrafluorborate ([BF4]~-) anion were obtained by the DC magnetron sputtering of high-entropy alloy target in vacuum, onto the surface of [BMIM.BF4] ionic liquid. The method of the nanoparticle colloid preparation is based on negligibly small vapour pressure of the ionic liquid, which allows its application in vacuum. The high-entropy alloy nanoparticle colloids were studied by HRTEM microscopy and SQUID magnetometry. Results of the structural and magnetic analyses show that the colloids contain ultra-small single-crystalline nanoparticles of an uneven shape and typical size of (2-3) nm. The nanoparticles have relatively narrow size distribution which is typical for this preparation method. The high-entropy alloy nanocolloids show complex magnetic properties that are a function of temperature, applied magnetic field and mass content of the nanoparticles in the colloids. The obtained results imply significant magnetic interactions between the ionic liquid and the high-entropy alloy nanoparticles.
查看更多>>摘要：To explore the ductility and deformation nature, a new Mg-2.76Li-3Al-2.6Zn-0.39Y alloy has been successfully fabricated by decreasing-temperature multidirectional forging and hot rolling. The maximum elongation to failure of 223.0% was demonstrated in this alloy at a temperature of 633 K and a strain rate of 1.67 × 10~(-4) s~(-1). Flow stress curves and microstructural examination showed that continuous dynamic re-crystallization occurred in this alloy at different temperatures and strain rates in most cases, but the flow hardening phenomena appeared at a temperature of 603 K at a strain rate of 5× 10~(-4) s~(-1) and at 573,603 and 633 K at a strain rate of 1.67 × 10~(-4) s~(-1). A criterion of grain size changing rate was proposed to judge the occurrence of microstructural evolution mechanisms. A modified Johnson-Cook constitutive model established in this alloy was incorporated into dislocation models to realize the estimation of the dislocation density and the number of dislocations under specific conditions. A power-law constitutive equation was established in this alloy. The relationship between average grain size and Zener-Hollomon parameter was established. It was found that the stress exponent was 3.26, and the average experimental activation energy for deformation was 143.67 kj/mol; the dislocation density was 3.25 × 10~(13) m~(-2), and the number of dislocations was 59 at 633 K and 1.67 × 10~(-4) s~(-1). All of these results indicate that the predominant deformation mechanism of this alloy under this condition is dislocation glide creep controlled by lattice diffusion.
查看更多>>摘要：The cylindrical Sn: β-Ga_2O_3 crystal with high crystalline quality was successfully designed and grown by the innovative edge-defined film-fed growth (EFG) method equipped with a cylindrical Iridium die. The challenges for the growth of Sn: β-Ga_2O_3 crystals were overcome by optimizing the design of an afterheater. The growth morphology of cylindrical β-Ga_2O_3 crystal was studied using a theoretical model and the results from experimental crystal growth. The order of importance of growth conditions affecting β-Ga_2O_3 crystal growth morphology was examined, based on the morphological features of cylindrical β-Ga_2O_3 crystals obtained by the EFG and Czochralski methods. The iridium inclusions with three shapes were observed in bulk β-Ga_2O_3 crystal, and the formation mechanism was carefully discussed. The optical bandgap and valence band maximum (VBM) of Sn: β-Ga_2O_3 crystal were calculated to be 4.74 eV and 3.49 eV by absorption spectra and X-ray photoelectron spectroscopy (XPS), respectively. The corresponding surface barrier height (φ_(surf)) was 1.25 eV. The carrier concentration of 5.95× 10~(18) cm~(-3) was characterized by capacitance-voltage (C-V) measurement. By the Hall measurement, the carrier mobility and resistivity were estimated to be around 51 cm~2 V~(-2) s~(-1) and 3.55 ×10~(-2) Ω cm, respectively.
查看更多>>摘要：This work reports the high performance of NiCo-layered double hydroxide (NiCo-LDH) self-growing nanosheet arrays decorated with graphitic carbon nitride (g-C_3N_4) as a potential electrode material for supercapacitor. The composite is prepared by a convenient microwave method and its electrochemical behavior is evaluated. In three electrode system, the graphitic carbon nitride-NiCo-layered double hydroxide (CN-LDH) electrode exhibits high specific capacitance of 1936.36 F g~(-1) at 1 A g~(-1). The results show that adding a certain amount of g-C_3N_4 to LDH can significantly increase the specific capacitance of the electrode. In addition, the electrochemical performances of the electrode are further studied by Density functional theory (DFT) calculations and capacitance contribution fitting, which provides theoretical assistance for the elaborated electrochemical performance and reaction kinetics. Meanwhile, the possible reaction mechanisms are explained from two aspects of current density and scan rate, which revealed a reference idea for the future recombination of g-C_3N_4. The supercapacitor is assembled to verify the practical application of the CN-LDH electrode, CN-LDH//AC displays the maximum energy density of 50.63 Wh kg~(-1) at the power density of 0.80 kW kg~(-1), and successfully lights several LEDs. This confirms that the self-growing nanosheet arrays CN-LDH electrode possesses the potential value for supercapacitor applications.
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：To recover the remanence (or maximum energy product ((BH)_(max))) and squareness with high coercivity in diffusion-processed hot-deformed Nd-Fe-B magnets, new efforts have been made in this work. Annealing at a selected temperature of 800 °C under pressure was applied to the hot-deformed magnets diffused by the Nd_(70)Cu_(30) or Nd_(70)Cu_(15)Ga_(15) alloy. After this process, the thick powder boundary phase dissolved in the matrix and diffused into the intergranular regions. The c-axis misalignment of Nd_2Fe_(14)B grains near the diffusion surface was significantly improved, leading to increased remanence by 0.10-0.18 T and (BH)_(max) by 47-85 kj/m~3 in the two diffusion-processed magnets. The distribution of the powder boundary phase, the proportions of the intergranular Nd-rich phase, the c-axis alignment of grains and the grain sizes from the diffusion surface to the center of the magnets tend to be relatively uniform. The squareness factor of the demagnetization curve increased from 0.89 to 0.95 for the Nd_(70)Cu_(30)-diffused magnet and from 0.85 to 0.93 for the Nd_(70)Cu_(15)Ga_(15)-diffused magnet after the process, returning to the level of the as-deformed magnet. Microstructure analysis and micromagnetic simulations indicate that the improved squareness factor is due to the homogeneous magnetization reversal process caused by the homogeneous microstructure.
查看更多>>摘要：We report a novel mechanoluminescent phosphor Li_(1-x)Ca_xSi_xTa_(1-x)O_3:0.01Pr~(3+) (x = 0-0.04). The crystal structure, photoluminescence (PL), optical diffuse reflectance spectra, afterglow (AG), fluorescence decay curves, and mechanoluminescence (ML) properties were investigated. To clarify the defect types and the mechanoluminescence mechanisms, an X-ray photoelectron spectroscopy (XPS) and thermoluminescence curve (TL) were measured. The dopants Ca~(2+) and Si~(4+) ions occupied the Li+ and Ta~(5+) sites, respectively. An optimal sample Li_(0.98)Ca_(0.02)Si_(0.02)Ta_(0.98)O_3:Pr~(3+) was obtained with great enhancement in mechanoluminescence intensity, higher than that of non-doped sample LiTaO_3:Pr~(3+) by 262%. And the compression threshold, over which the ML intensity could not maintain the linear increase, has also been greatly improved. Furthermore, the stable output of Tribo-L was achieved, which was visible to the naked eye. A probable mechanism was proposed to illustrate the mechanoluminescent process in Lil-xCaxSixTal-xO3:0.01Pr3 + (x = 0-0.04). The study indicates that adjusting trap distribution by substituting host ions may be a novel way to develop high-quality mechanoluminescence.
查看更多>>摘要：Four new Bi(III) phosphates, K_6Bi_(13)(PO_4)_(15), K_5Bi(P_2O_7)_2, and A_5Bi_5(PO_4)_4(P_2O_7)_2 (A= K, Rb) with the different condensed P-0 groups have been successfully synthesized via the solid-state reactions. The single crystals X-ray diffractions show that they crystallize in the different space groups (K_6Bi_(13)(PO_4)_(15): C2; K_5Bi(P_2O_7)_2: P1; K_5Bi_5(PO_4)_4(P_2O_7)_2 and Rb_5Bi_5(PO_4)_4(P_2O_7)_2: P2_1/c). The structure of K_6Bi_(13)(PO_4)_(15) can be described as a three-dimensional (3D) network composed of the Bi-0 polyhedra and PO_4 tetrahedra with K atoms filling in the space to balance the residual charges. K_5Bi(P_2O_7)_2 features 2D [BiP_4O_(14)]_∞, layers built by the BiO_6 oc-tahedra and P_2O_7 dimers and the adjacent [BiP_4O_(14)]_∞ layers are bridged by the K atoms. A_5Bi_5(PO_4)_4(P_2O_7)_2 (A = K, Rb) contain two different condensed P-0 groups, PO_4 tetrahedra and P_2O_7 dimers, which are connected by Bi-0 polyhedra to construct the complicated 3D framework with K/Rb atoms located in the tunnels. Note that, the compounds that simultaneously contain two different types of P-0 groups are still rare in phosphates. Detailed structural comparisons of Bi~(3+)-containing phosphates indicate that the Bi/P ratios have a significant effect on the condensed degrees of PO_4 groups. Furthermore, TG-DSC, IR, UV-Vis-NIR diffuse reflectance spectra and SHG test for title compounds have also been reported.
查看更多>>摘要：The recent development of electronic devices and control over their electro-magnetic and thermoelectric characteristics via electron spin has attracted a significant attention. Herein, we have addressed magnetic and thermoelectric calculations of K_2MZ_6 (M = Os, Ir, and Z = CI, Br) by quantum simulations. By comparing energies in antiferromagnetic, and ferromagnetic states, it turns out that lower energy corresponds to ferromagnetic (FM) states. Further, to confirm structural stability of FM state, tolerance factor was utilized. The Curie temperature has been reported by Heisenberg classical model. Moreover, the band structures (BS) and density of states (DOS) were analyzed to categorize half metallic (HM) ferromagnetism. To deeply understand the governing Half metallic ferromagnetism, the partial DOSs was tackled by p-d hybridization, exchange energies, and double-exchange model. The system is 100% spin polarized which is assured by integer magnetic moment.
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.
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Elsevier