查看更多>>摘要：Antiferroelectric materials are considered promising energy storage materials because they have excellent energy density during the antiferroelectric phase transition. Herein, Pb_(0.925)La_(0.05)Zr_(0.95)Ti_(0.05)O_3@SiO_2 (PLZT@SiO_2) core-shell structure ceramic materials were synthesized by combing sol-gel method with conventional solid-phase method. The effect of holding time (3 h, 6 h, 9 h, 12 h) on the electrical properties and energy storage properties of PIZT@SiO_2 ceramics were investigated. TEM results indicate the formation of a core-shell structure. Transmission electron microscope (TEM) reveals the formation of core-shell structure. X-ray diffraction (XRD) obtained clear tetragonal perovskite structure PLZT and SiO_2 phase. The phase transition temperature of PLZT@SiO_2 ceramics is between 222 °C and 225 °C, and its dielectric constant can be adjusted by the holding time. The PLZT with surface coated SiO_2 can increase the breakdown electric field (BDS) and thus increase the energy density. When the holding time is 9 h, the breakdown electric field is as high as 156.84 kV/cm, and the recoverable energy density (W_(re)) is 1.92 J/cm~3, which is mainly determined by its high density and breakdown electric field.
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 liquid-solid phase transitions and solidified microstructures of highly undercooled Fe-Zr eutectic melts were investigated by the drop tube technique. The quantitative relationships among droplet diameter (D), undercooling (ΔT) and cooling rate (R_c) were calculated for three types of eutectic alloys (Fe-9.8 at. % Zr, Fe-6 at. % Zr and Fe-16 at. % Zr alloys). Furthermore, the evolutions of solidified microstructure with droplet diameter were studied. The results show that the eutectic microstructure for Fe-9.8 at. % Zr droplet transforms from regularly lamellar shape to anomalous shape as the diameter reduces. The α-Fe dendrite in Fe-6 at. % Zr droplet transforms from coarse dendrite to refined dendrite with the decrease of droplet diameter, while the Fe_2Zr dendrite in Fe-16 at. % Zr droplet transforms from faceted dendrite to non-faceted grain. Besides, a remarkable solid solubility extension was found in both the α-Fe dendrites of Fe-6 at. % Zr alloy and the Fe_2Zr dendrites of Fe-16 at. % Zr alloy. The solid solubility of the a-Fe dendrite increases from 3 at. % to 5.6 at. % when the droplet diameter reduces from 1069 to 212 um, while it decreases from 31 to 22 at. % in the Fe_2Zr dendrite as the diameter reduces from 991 to 228 um. The microstructural morphology and solid solubility are directly related to the nano-hardness and Young's elastic modulus of alloys. The nano-mechanical properties of the eutectic gradually increase with the refinement of the layers, and gradually decrease as the irregularity of the anomalous eutectic increases. With the reduction of droplet diameter, the nano-hardness rises and Young's elastic modulus continuously diminishes for the a-Fe dendrite due to the increase in the solute content of Zr, while these two mechanical properties gradually decrease for the Fe_2Zr dendrite because of the reduction in the solute content of Zr.
查看更多>>摘要：Single step hydrothermal method was used to synthesize molybdenum disulfide (MoS_2) thin films. The hexagonal structure of MoS_2 was confirmed by X-ray diffraction techniques (XRD). The nanosheets like morphology of MoS_2 films were confirmed using scanning electron microscopy (SEM). The optical band gap of pristine MoS_2 was found to be -1.53 eV. The prepared MoS_2 films were irradiated with ion and gamma radiation at different ion fluence and doses respectively. For ion irradiation, the samples were irradiated at ion fluences of 4.7 × 10~(16) ion/cm~2, 7.1 × 10~(16) ion/cm~2, 9.5 × 10~(16) ion/cm~2,11.9 × 10~(16) ion/cm~2 and 14.3 × 10~(16) ion/cm~2. In case of gamma irradiation, the samples were irradiated for 10 kGy, 100 kGy, 300 kGy, and 500 kGy and 800 kGy doses. The tensile strain induced in the sample was studied with the help of Raman spectroscopy and XRD technique. The defect induced tensile strain in MoS_2 films due to ion irradiation is higher as compared to gamma irradiation.
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：A multiphase AlMo_(0.8)NbTiW_(0.2)Zr refractory multi-principal element alloy (RMPEA) with superior elevated-temperature strength was prepared by the powder metallurgy (PM). The as-sintered RMPEA was composed of BCC matrix, lath-like B2 phase, and two Al-Zr hexagonal structure phases. The alloy (p = 7.07 g/cm3) exhibited a superior specific compressive yield strength of 153.3,107.8 and 54.7 MPa cm~3/g at the temperature of 1423,1523 and 1623 K, respectively, which were remarkable in the current designed refractory alloys. After compressing at 1423 K, the AlMo_(0.8)NbTiW_(0.2)Zr consisted of a band-like or blocky Zr_5Al_4-type phase and the BCC matrix, in which embedded amounts of spherical B2 nanoparticles with a size of 5-10 nm. The superior elevated-temperature compressive yield strength of the RMPEA at 1423 K is primarily ascribed to both the stabilization of the martensitic-transformation Zr_5Al_4-type submicron-sized phase and the precipitation of the B2 nanoparticles, afterwards impede the deformation flow.
查看更多>>摘要：We prepared a novel three dimensional (3-D) 3d-4f MOF (named as CeCu-MOF; C_(10)H_(10)CeCu_2N_4O_(12)) which exhibits triclinic symmetry P-1 space group, and applied it to the study of electrode materials in organic system and aqueous solution system respectively. In order to overcome the shortcomings of poor electrical conductivity of MOF, we prepared several plant-charcoal materials with discarded grapefruit peel by different carbonization methods. The best electrochemical performance is selected for detailed study. In this paper, different amounts of plant-charcoal and MOF were used as electrode materials for supercapacitors and lithium-ion batteries, and their electrochemical properties were investigated. The results showed that the addition of plant-charcoal did help to improve the electrochemical performance compared with the single-phase MOF.
查看更多>>摘要：The pigments with high near-infrared (NIR) reflectance hold great promise toward both fundamental types of researches and applications for the realization of comfortable indoor-temperature by mitigating urban heat island effect. However, the facile yet simple method for the NIR reflective pigments with bright color and non-toxic feature remains a huge challenge, limiting their practical application. Herein, we proposed a mild and universal method of solution combustion for constructing the non-toxic and NIR reflective yellow-green pigments of Al-doped Y_3Fe_5O_(12). The Y_3Fe_4AlO_(12) pigment presented a high NIR reflectance of 87.66%, and an outstanding acid/alkali resistance. Moreover, the pigment had an impressive color performance (L* = 78.72, a* = - 4.05, b* = 40.04). Besides, the practical near-infrared reflection performance revealed that the transient surface temperature of the Y_3Fe_4AlO_(12) pigment was 7.6 °C lower than that of the pigment with similar color on the market. This research supplied high NIR reflecting pigments of Y_3Fe_(5-x)AlO_(12) as promising coatings for roofs and exterior walls of buildings, acting as a favorable solution for urban heat island effect.
查看更多>>摘要：Transition metal dopant engineering and rational architecture design have been proven to be effective strategies to improve the electrochemical energy storage properties of electrodes. Herein, V-doped NiMn-layered double hydroxide composites were supported on reduced graphene oxide-coated Ni foam (NMV-L/ rGO) by a hydrothermal method. The influences of V content on the electrochemical performances of NMV-L/rGO composites were investigated in detail. At an optimal content of V doping (15%), the NMV-L/rGO-15 reveals enhanced electrochemical properties, and it is subsequently applied as the substrate for the elec-trodeposition of Ni_3S_2 layer. Benefiting from the collaborative effect of NMV-L/rGO-15, Ni_3S_2, and rGO materials, as well as the unique hierarchical architecture, excellent electrochemical performance is obtained in the as-prepared Ni_3S_2 @NMV-L/rGO-15 composite, which exhibits a high specific capacity of 1412.0 C g~(-1) at 1 A g~(-1) as well as desirable long-term stability of 89% over 5000 cycles. Furthermore, the as-fabricated battery-supercapacitor hybrid device (BSH) based on Ni_3S_2@NMV-L/rGO-15 and activated carbon (AC) electrodes displays a remarkable energy density of 60.0 W h kg~(-1) at the power density of 849.1 W kg~(-1) and superior capacity retention of 96% through 7000 cycles. Such excellent results indicate that the Ni_3S_2 @ NMV-L/rGO-15 composite holds great potential as electrode material for high-performance BSHs.
查看更多>>摘要：Fe-based nanocrystalline alloys with unique dual-nano-phase structure and superior magnetic softness have aroused tremendous interest, yet they generally suffer from the harsh annealing process due to the poor thermal stability. In this study, a high-entropy strategy was proposed to enhance the soft-magnetic property and nanostructure stability of Fe-based nanocrystalline alloys by adding P and C elements in the FeCuSiBPC alloy system. This alloying approach by complicating the composition will greatly increase the mixing entropy, which significantly increase the frequency factor for the formation of α-Fe grains and activation energy for the formation of compounds, which on one hand enhance the competition and soft-impingement effects due to the increased number density of a-Fe grains, and on the other hand hinder the precipitation of compounds in the intergranular amorphous interphase due to the improved crystallization resistance. These both contribute to a thermodynamically and kinetically stable dual-nano-phase structure with fine a-Fe grains embedded in amorphous matrix. Following this strategy of nanostructure stabilization by tuning the compositional complexity, FeCuSiBPC alloy with enlarged processing window and enhanced soft-magnetic properties were successfully obtained. This high-entropy strategy can be applied in a verity of alloy systems to develop high performance nanocrystalline alloys with excellent thermal stability suitable for large-scale industrial processing.
NSTL
Elsevier