查看更多>>摘要：Antiferromagnetic pyrite compound MnTe_2 is a newly discovered high-performance thermoelectric material. However, its electric and thermal transport performance remained unexplored so far. In this work, the first-principle calculations based on the density functional theory were applied to predict the electric and thermal transport performance of MnTe_2. The band structures showed that Te atoms dominate the band energies near the fermi level. The calculated electric transport performance of MnTe_2 from BoltzTraP2 package showed that n-type MnTe_2 possesses a higher power factor than that of p-type in the carrier concentration range from 10~(19) to 10~(21) cm~(-3). The peak power factor with electronic relaxation time of n-type MnTe_2 at 800 K is 3.05 x 10~(15) μW K~2 cm~(-1) s~(-1) at a lower carrier concentration of 0.78 × 10~(21) cm~(-3) while p-type is 2.18 × 10~(15) μW K~(-2) cm~(-1) s~(-1) at a higher carrier concentration of 1.35 × 10~(21) cm~(-3) It suggests that high-performance n-type doped MnTe_2 is easier to be obtained experimentally. Due to the low average phonon velocity of 2064 m-s~(-1), MnTe_2 has a low lattice thermal conductivity of 0.72 W m~(-1) K~(-1) at 800 K. The calculated charged point defect formation energy of several possible n-type doping elements showed that Y or La substituting Mn atom and Cl or Br substituting Te atom are the most possible n-type doping point defects. Combined with the optimal carrier concentration of 0.78 x 10~(21) cm~(-3)at 800 K, stoichiometric A_(0.07)Mn_(0.93)Te_2 (A = Y, La) and MnTe-1.93B0.07 (B = Cl, Br) are expected to possess high thermoelectric properties reaching the theoretical peak power factor with electronic relaxation time of 3.05× 10~(15) μW K~(-2) cm~(-1) s~(-1) and the lattice thermal conductivity of 0.72 W m~(-1) K~(-1).
查看更多>>摘要：Transition metal oxides have achieved tremendous attention in the field of supercapacitor devices due to their outstanding structural properties and capacitive behavior. Herein, a porous a-MoO_3 microspheres (A-SMO) were synthesized with the aid of CrCl_3.6H_2O via a facile hydrothermal reaction and subsequent annealing treatment. The results showed that CrCl_3.6H_2O plays a crucial role in manipulating morphology and increasing the specific surface area of the as-prepared products. Moreover, annealing treatment could transform the crystal structure from metastable hexagonal M0O_3 to stable orthogonal MoO_3, which is more beneficial for electron storage due to the layered crystal structure. Furthermore, the A-SMO displayed an excellent specific capacitance of 201.4 F g~(-1) compared with the pristine MoO_3 (MO) of 62.0 F g~(-1) and the annealed MO (A-MO) of 186.5 F g~(-1) at 0.2 A g~(-1), when they were directly served as supercapacitor electrodes. This research demonstrates that the as-obtained a-MoO_3 microspheres can serve as promising electrode materials for supercapacitors.
查看更多>>摘要：Flexible supercapacitors (SCs) can usually be used as potential candidates for small flexible electronic devices, due to their good flexibility, rapid charge-discharge ability, and long-term cycling stability. Here, a facile solvothermal approach has been developed to prepare flexible and high-performance nitrogen-doped Ti_3C_2 MXene film electrodes for symmetric SCs. The effects of different solvents on the atomic structure, surface microstructure, and charge storage mechanism of N-doped Ti_3C_2 films were studied to explore the defect engineering of MXene for the enhancement of capacitive performance. Because of the comprehensive effects of the mixed solvents (diethanolamine (DEA) and isopropyl alcohol (IPA)) and the large inner pressure under the ex situ solvothermal process, the as-prepared N-doped Ti_3C_2 film fabricated from DEA and IPA with a volume ratio of 1:1 (IPAD-Ti_3C_2) shows a superhigh capacitance of 2846.5 F cm~(-3) at 5 mV s~(-1) and excellent stability. In addition, the IPAD-Ti_3C_2 film-assembled symmetric SC delivers a relatively large volumetric energy density of 64.0 Wh L~(-1) and a superhigh volumetric power density of 118,033.3 W L~(-1) at 1000 mV s~(-1). This work provides a feasible solution to improve the application potential of MXenes and, more broadly, binary metal carbides by ex situ nitrogen doping with mixed solvents.
查看更多>>摘要：Multi-principal-element alloys (MPEAs) are a wide class of materials currently at the center of numerous investigations. Key-issues with MPEAs are related with controlling the onset of (i) long-range order and (ii) phase separation, both processes being in general detrimental to the properties. While trends (i) and (ii) are strongly dependent on the precise proportions of metallic elements around the reference equiatomic MPEA, the tremendously large composition space makes it a tricky task to heuristically identify optimized MPEAs. In practice, this often leads to undesired second-phase ordered particles. This deficiency emphasizes the relevance of modelling and simulation tools designed to facilitate the exploration of MPEA composition spaces. In this atomic-scale work, we propose a "composition-constrained" point mean-field formalism resting on alloy pair energetics, to investigate trends (i) and (ii). This formalism is currently applicable to a wide panel of such systems built from ~ 30 chemical elements. Its application to several MPEAs along the AlCoCrFeNi → AlCrFeMnNi→ AlCrFeMnMo sequence evidences striking differences between these systems, and demonstrates its efficiency to get at-a-glance information about (i) and (ii) features for various MPEAs. The flexibility of the proposed simulation approach makes it easily employable in conjunction with experiments on well-equilibrated MPEA samples, for thermodynamic characterizations of MPEAs.
查看更多>>摘要：In this work, to enhance the mineralization of the organic dyes, the g-C_3N_4(Ag)/Gr/TiO_2 Z-scheme photo-catalyst was successfully prepared by hydrothermal method. The XRD and XPS results showed that the nanocomposite was constructed. The SEM and EDS results showed that the morphology of g-C_3N_4(Ag)/Gr/ TiO_2 was that TiO_2 nanoparticles distributed on the surface of the Gr/g-C_3N_4 layers. The photocatalytic performance of the prepared samples was evaluated by the photocatalytic degradation and mineralization of RhB under visible light irradiation. The degradation efficiency of RhB on g-C_3N_4(Ag)/Gr/TiO_2 reached 99.7% within 2 h, and the kinetic rate (0.0431 min~(-1)) was 7.1, 7.1, 2.2, 2.0 and 1.3 times higher than those of g-C_3N_4, TiO_2, g-C_3N_4(Ag)/Gr, g-C_3N_4/TiO_2, and g-C_3N_4/Gr/TiO_2, respectively. The total organic carbon (TOC) removal results showed that the mineralization efficiency of RhB on this composite was as high as 74.5% after 2 h of reaction time. During the photocatalytic process, it was speculated that Gr acted as the electron transporter between TiO_2 and g-C_3N_4, which reduced the recombination efficiency of photo-generated charge carriers, and silver clusters acted as an electron reservoir to accelerate the reduction reaction of photo-generated electrons on the g-C_3N_4 conduction band, and further improved the photocatalytic performance.
查看更多>>摘要：By the exploitation of doping in semiconductor photocatalysts, the energy band structure adjustment would induce the improvement of solar absorption and photochemical performance. Here, we investigated the N/F codoped TiO_2 nanotube arrays (TiO_2 NTs) by tuning the preparation operation sequence of sol-vothermal doping and annealing treatment. The optimized Sample 1 prepared by the first solvothermal doping in ethanol and then annealing exhibited the outstanding solar absorption, low electron-hole recombination and photoelectrochemical performances. The excellent photocatalytic performances in pho-tocurrent/H_2 generation and pollutant removal were discussed and analyzed in detail. Furthermore, we explained the mechanism of N/F codoping for improved photocatalytic performances. The work gives a referable template for improved photocatalytic application fields of TiO_2 in environment and energy.
Ismayadi IsmailMuhammad Misbah Muhammad ZulkimiRaba'ah Syahidah Azis
7页
查看更多>>摘要：In the present work, substitution of strontium U-type hexaferrite with the composition of Sr_4Mn_(2-x)Zn_xFe_(36)O_(60) (x= 0.5,0.6,0.8, and 1.0) was prepared via high energy ball milling (HEBM) and sintered at 1100 °C. The phase, microstructure, magnetic, dielectric and electromagnetic wave absorbing properties of U-type strontium hexaferrite composites were measured using XRD, FESEM, and Vector Network Analyzer in the frequency range of 8-18 GHz (X-band and Ku-band). MnZn doping was found to shift the natural resonance of the materials by affecting its magnetocrystalline anisotropy. The reflection loss (RL) indicated that the composite possessed good microwave-absorbing properties with U-type strontium hexaferrite ( Sr_4Mn_(2-x)Zn_xFe_(36)O_(60)) of x = 0.8 resulted in high minimum RL value for all thickness of 1 mm and two peaks at approximately - 32.50 and - 41.50 dB at 14.00 and 15.60 GHz, with bandwidth of 0.60 and 0.80 GHz for losses less than - 10 dB.
查看更多>>摘要：Electron backscatter diffraction (EBSD) was applied to investigate the superplastic behavior of a fine-grain Al-Mg-Li alloy. It was found that microstructural changes were noticeably influenced by the occurrence of continuous dynamic recrystallization. This mechanism involved a transverse subdivision of pre-elongated grains which eventually transformed into chains of nearly-equiaxed grains. A body of experimental observations, including extensive strain hardening, marked grain elongation, the formation of pronounced substructure in interior regions of grains, and the development of crystallographic texture, provided strong evidence of large amounts of intragranular slip operating during superplastic flow.
查看更多>>摘要：As-explosive welded clad plates usually show poor ductility due to heavily deformed microstructures developed after explosive welding (EXW). In this study, the feasibility of improving mechanical properties of an EXWed Mg-6Al-1Zn-lCa (AZX611)/AI-0.6Mg-0.6Si-0.1Fe (A6005C) (all in wt%) clad plate has been explored by subsequent hot-rolling. Increasing the thickness reduction per pass from 10% to 28% or decreasing the rolling temperature from 430 °C to 250 °C is shown to enhance tensile properties. The joint sheet rolled at 250 °C with a thickness reduction per pass of 28% shows a large fracture elongation of 15%, which is significantly higher than that of the as-EXWed clad plate, 1.2%. Microstructure characterization by means of scanning electron microscope, electron backscatter diffraction and transmission electron microscope reveals that the substantial improvement in ductility is intimately related to a significant reduction of the accumulated strain in AZX611 and A6005C alloy sheets and an elimination of the interface delamination formed during EXW. A certain degree of anisotropic mechanical properties is observed in all sheets regardless of rolling conditions, which can be ascribed to the mechanical anisotropy originated from the AZX611 and A6005C alloy sheets.
查看更多>>摘要：The high-entropy effect suggests the possibility of unusual thermal transport properties that may be favorable for thermoelectrics. Novel perovskite-type high-entropy (Ca_(0.25)Sr_(0.25)Ba_(0.25)La_(0.25))TiO_3 (4La) and (Ca_(0.25)Sr_(0.25)Ba_(0.25)Ce_(0.25))TiO_3 (4Ce) ceramics were successfully prepared through a conventional solid-state reaction method. XRD, SEM-EDS, and HRTEM were performed to confirm that the chosen multi-component cations can be introduced into A-site to form a single cubic phase with Pm-3m space group. Introduce high-entropy engineering, constituent elements competing inter into the A-site creating lattice distortion and strain fields, which results in extensive structural defects including dislocations which contributed to the phonons scattering of mid wavelength. Grain boundaries and intrinsic oxygen vacancies respectively scatter phonons of high and low wavelengths. The enhanced effective scattering of phonons through the multi-scale defects gives rise to a low lattice thermal conductivity of 2.5 W-m~(-1)-K~(-1) at 1073 K for the 4La ceramics, much lower than that of SrTiO_3-based perovskite thermoelectric ceramics. The high-entropy 4La ceramics possess the maximum power factor of 420 μW-m~(-1)K~(-2). This work provides a strategy of compositional design for thermoelectric oxides with decreased intrinsic thermal conductivity for thermoelectric applications.
NSTL
Elsevier