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.
Evgeny V. ZharikovValentina B. DudnikovaNina G. Zinovieva
8页
查看更多>>摘要:The content of all matrix elements, including oxygen, was determined by X-ray spectral microanalysis in series of single crystals of sodium-gadolinium molybdates (NGM) grown from melt by Czochralski technique. All grown NGM crystals, including those grown from stoichiometric charge, are non-stoichiometric and contain a molybdenum deficiency of about 3% in average. The NGM congruently melting composition has been determined. For crystals grown from melt of equimolar (stoichiometric) composition, the content of cationic vacancies in the (Gd + Na) sublattice is close to zero, while the composition of crystal differs from the initial melt. As the Gd excess increases, the content of cationic vacancies in the (Gd + Na) sublattice increases up to 10%. It has been found that cation-deficient NGM crystals are also ahion-deficient. The concentration of oxygen vacancies varies from 0.5% to 5% of the amount of anion sites. Possible mechanisms responsible for the formation of cationic and anionic vacancies in NGM crystals are discussed.
查看更多>>摘要:Grazing incidence X-ray diffraction (GIXRD) and scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS) were employed to study the microstructure evolution and stress development in the nanocrystalline Cu_(100-x)-Zr_x (2.5 at% ≤ x ≤ 5.5 at%) alloy thin films. Small Zr additions to Cu led to significant lattice parameter anisotropy in the as-deposited Cu-Zr thin films both due to macroscopic lattice strain and stacking faults in the Cu matrix. Strain free lattice parameters obtained after the XRD stress analysis of Cu-Zr thin films confirmed formation of a supersaturated substitutional Cu-Zr solid solution. For the first time, the study of film microstructure by XRD line profile analysis (XLPA) confirmed progressive generation of dislocations and planar faults with increasing Zr composition in Cu-Zr alloy films. These microstructural changes led to the generation of tensile stresses in the thin films along with considerable stress gradients across the films thicknesses which are quantified by the traditional d_ψ~(hkl) - Sin~2 ψ and GIXRD stress measurement methods. The origin of tensile stresses and stress gradients in the Cu-Zr film are discussed on the basis of film growth and heterogeneous micro-structure with changing Zr composition.
查看更多>>摘要:Zinc ion batteries (ZIBs) are newly emerging and widely attracted energy storage devices owing to its advantages of intrinsic safety and low-cost effectiveness. Herein, we reported a nanorod-like MnO_2 cathode material composited with carbon and pyrrolic nitrogen by in-situ co-precipitation method at room temperature, which was used as ZIB cathode to deliver a high specific capacity of 339 mAh g~(-1) at 100 mA g~(-1) and a long cycle stability over 2000 cycles at 1000 mA g~(-1), resulting in the ultrahigh coulombic efficiencies approximate to 100%. The improved performance was attributed to the enhancement of structural stability and more zinc ion insertion sites after introducing the 2-methylimidazole (2-MI) coating layer. The phase transition of α-MnO_2 @2-methylimidazole (α-MnO_2 @2-MI) and the formation of more porous architecture could be the origin of the continuous capacity increasing in the initial several cycles, which was proved by the results of the ex-situ x-ray diffraction (XRD) and the scanning electronic microscope (SEM). This method can be a more realistic choice for the further commercial applications of low-cost and easily-accessed ZIBs with excellent electrochemical performance.
查看更多>>摘要:Nonlinear-optical (NLO) metal aluminium phosphate crystal materials with deep-ultraviolet (DUV) transparent ability remain greatly unexplored. Herein, mixed alkali/alkaline-earth metal aluminium phosphate DUV NLO crystal Na_2Ca_(17)Al_2(PO_4)_(14) was successfully synthesized through the high-temperature molten technology. Na_2Ca_(17)Al_2(PO_4)_(14) features a 3D Ca-cluster-constructed framework by the stacking of Ca_6O_(36) and (Ca/Na)_3O_(19) clusters, which is filled by isolated A1(PO_4)_6 clusters and isolated PO_4 tetrahedra. Na_2Ca_(17)Al_2(PO_4)_(14) exhibits a short UV absorption edge below 190 nm, phase-matching behavior with strong NLO effect of 0.9 × KDP, high thermal stability. First-principles calculations indicate that the optical properties of Na_2Ca_(17)Al_2(PO_4)_(14) derive primarily from the Ca-O groups, rather than Al-O and P-O traditional groups. The work may further promote the exploration of new DUV NLO aluminium phosphate crystal materials.
查看更多>>摘要:In this study, the electrocaloric (EC) effect was enhanced at room temperature for (Ba_(0.904)Ca_(0.096)) (Zr_(0.136)Ti_(0.864)-xFe_x)O_3 (BZT-0.32BCT-xFe 0 ≤ x ≤ 0.015) thin films prepared on Pt/Ti/SiO_2/(100)Si substrates. The existence of an orthorhombic phase in the Fe-doped thin films at room temperature was confirmed by X-ray diffraction and Raman spectra. Tetragonal, orthorhombic, and rhombohedral phases coexist in all the investigated Fe-doped thin films. The relative content of the orthorhombic phase is most prominent at x = 0.0075. The BZT-0.32BCT-xFe thin film exhibits excellent properties with a giant EC effect (ΔT = 22.99 K, E = 1050 kV/cm, and T = 307 K) at x = 0.0075 compared to the undoped thin film, stemming from multiphase coexistence and a larger orthorhombic phase. The results of this study are useful for developing lead-free electrocaloric materials with superior properties.
查看更多>>摘要:In the present study, the amorphous Ti-Ni-Zr-Cu thin ribbons were successfully prepared through rapid spinning technology. The crystallization temperature of Ti-Ni-Zr-Cu thin ribbon increased with the increasing of heating rate. The activation energy of crystallization for Ti-Ni-Zr-Cu thin ribbon is calculated to be 156 kj/mol, which is remarkably lower than that of the reported Zr-Cu based metal glass due to the smaller negative enthalpy of mixing atomic pairs. The phase constituents of annealed Ti-Ni-Zr-Cu thin ribbons were largely related to the annealing temperatures. The phase constitutes of Ti-Ni-Zr-Cu thin films annealed at the temperatures lower than 850 °C is almost equal, but the lattice constant of various phases is gradually reduced with the increasing of annealing temperatures. In proportion, Ti-Ni-Zr-Cu thin ribbons annealed at the temperatures lower than 750 °C show the higher Vickers hardness, while a noteworthy reduction of Vickers hardness is observed in Ti-Ni-Zr-Cu thin ribbon annealed at 850 °C. Besides, the annealing temperature has a significant effect on the specific heat and corrosion properties, which can be attributed to the distinction of phase constituents.
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:Herein, porous Si_3N_4 ceramics embracing excellent mechanical and dielectric properties were achieved via gelcasting using N, N-dimethylacrylamide (DMAA) gel system while acting as pore-former. The increase of monomer content (8.0-23.0 wt%) led to an increase in porosity (39.53-43.60%) and pore connectivity, which accelerated vapor phase mass transport and promoted p-Si_3N_4 grain growth, thereby improving flexural strength (212.33-245.30 MPa) and fracture toughness (3.60-3.89 MPa-m~(1/2)). Attributable to the pores introduced by increasing monomer content, the e' and tanδ were significantly reduced with the values of 4.18-4.29 to 3.95-4.06 and 1.83-2.38 × 10~(-3) to 0.37-1.96 × 10~(-3), respectively, demonstrating excellent microwave-transparent properties. This work proved the great application potential of porous Si_3N_4 ceramics fabricated by gelcasting employing DMAA gel system in the field of microwave-transparent materials.
查看更多>>摘要:The poling of macro fiber composites (MFCs) as a vital part for manufacturing usable samples, is related with but different from that of their piezoelectric phase owing to the existence of interdigitated electrodes. Herein, beginning with the quantitative relationship between effective electric field and external electric field obtained by finite element analysis, the prediction and optimization of poling condition for lead zir-conate titanate (PZT) based-MFCs was presented. The results demonstrate that the predicted values agree with the experimental results, specifically, the poling field range of the investigated MFCs is from 16.7 kV/ cm to 33.3 kV/cm. The piezoelectric and dielectric properties of MFCs are improved by adjusting the poling condition up to a suitable value, whereas are degraded due to the interaction of domain alignment and electric field concentration. The optimal poling condition of the MFCs is 26.7 kV/cm for 10 min at room temperature. This research contributes to realizing the personalized-customization of MFCs.