查看更多>>摘要：? 2022 Elsevier B.V.It remains a huge challenge to enhance the energy-storage density (ESD) and efficiency (ESE) of Pb-free dielectrics for ES applications. However, most of the developed lead-free dielectrics do not have these properties due to some factors. In this study, 0.33BaTiO3-(0.67-x)BiFeO3-xBi(Mg2/3Ta1/3)O3 bulk relaxor-ferroelectric ceramic materials were established using a conventional solid-state technique, where a typical B-site composite perovskite-structured Bi(Mg2/3Ta1/3)O3 was used as an additive. The breakdown strength, relaxation behavior and ES performance of BaTiO3-BiFeO3 ceramics were improved after adding Bi(Mg2/3Ta1/3)O3 because of the generation of polar nanoregions (PNRs). The composite ceramics, with x = 0.10, demonstrated an excellent ESE (η) of 80.2 % and a high recoverable ESD (Wrec) of 3.0 J/cm3 at 240 kV/cm. In addition, the composite ceramics had high stability and good thermal stability in the frequency and temperature ranges of 0.5–100 Hz and 25–130 °C. These properties suggest that novel Bi(Mg2/3Ta1/3)O3-doped 0.33BaTiO3-0.67BiFeO3 ceramic is attractive for ES applications.
查看更多>>摘要：? 2022 Elsevier B.V.The pressure-dependent microstructure evolution of the gas-atomized Fe-based amorphous alloy powders at gas pressures in the range from 5 MPa to 8 MPa has been studied experimentally and theoretically. The results showed that the amorphous fraction and nucleation mode of particles were sensitive to the gas pressure. Specifically, at 7 MPa, the particles presented a fully amorphous structure with the maximal size class of 45–75 μm, and preferred to nucleate heterogeneously within the sphere rather than on the surface. These interesting phenomena were associated with the difference of cooling rate within droplets, reflected by the gas-liquid relative velocity at the cooling and solidification stage in the atomization process. It was also indicated that the amorphous phase underwent three stages of reactions upon devitrification with the precipitations of {Fe, Ni} and Fe2P, α-Fe and M23B6, respectively. Finally, glass-forming features of powders at different pressures have been elucidated based upon a kinetics analysis of the cooling rates of droplets and the phase selection competition. This work provides beneficial guidance for the devisal of metallic glass powder with different microstructures via gas atomization.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, CZTS samples were produced on Mo and graphene/Mo coated glass substrates using quaternary target. The CZTS thin films deposited by RF magnetron sputtering were annealed using rapid thermal processing (RTP) method in sulphur atmosphere at 500, 525, and 550 °C so as to obtain glass/Mo/CZTS and glass/Mo/graphene/CZTS (g-CZTS) structures. The obtained CZTS and g-CZTS thin films were then characterized by several methods such as EDX, XRD, Raman spectroscopy, SEM etc. The EDX data demonstrated that all CZTS thin films had Cu poor composition regardless of the sulfurization temperature and increasing the temperature led to Sn loss from the films. Diffraction peaks of kesterite CZTS phase were observed in all the samples; additionally, SnS and CuS secondary phases were also observed in CZTS samples annealed at 500 °C. The crystallite size of the CZTS thin films were found to be increasing with both increasing annealing temperature and use of graphene film as an inter-layer. The creation of kesterite phase with a very small CTS phase in all the samples were verified by the Raman spectroscopy measurement. The SEM images of the samples indicated that using graphene improves the crystalline quality of the CZTS films and contributes to forming more compact, homogenous and larger crystal structure. The determined optical band gap values varied from 1.41 to 1.44 eV depending on the Sn-content of the samples. The produced solar cells selected from the more promising absorber layers showed that implementing graphene in CZTS cell structure enhanced the conversion efficiency from 2.40% to 3.52% due to improvement of crystalline quality of the absorber layer.
查看更多>>摘要：? 2022 Elsevier B.V.β-C3N4 is one of the most difficult phases to synthesize among the C3N4 structures (α, β, cubic, pseudo cubic, and graphitic), and it has attracted marked attention because of its unique super hardness, optical properties, low density, good chemical resistance, and thermal stability. In this paper, a uniform β-C3N4 layer is successfully prepared and coated on a TiO2 nanotube substrate via a calcination treatment using ethylenediamine as the carbon nitride precursor. The as-obtained TiO2/C3N4 exhibites a promising sunlight-driven overall water splitting ability, with 1026.7 μmolH2 gcat.?1 h?1 and a 446.4 μmolO2 gcat.?1 h?1 generation rates simultaneously realized. Importantly, the turnover frequency for O2 in the photocatalytic splitting process reaches up to 4472.8 h?1 for the overall water splitting process, which is ~77.6 times that of the single β-C3N4 system (57.6 h?1) for O2 generation. In-situ Raman investigation demonstrates that N vacancy defects in β-C3N4 served as the active site for O2 generation from H2O, which is a hard nut to crack for C3N4 all the time.
查看更多>>摘要：? 2022 Elsevier B.V.Understanding the incipient plastic behavior of refractory high-entropy alloys (RHEAs) is crucial for their high-temperature applications. In this study, the initial dislocation nucleation and motion mechanisms in the TaTiZrV RHEA and their dependence on temperature were investigated upon nanoindentation by molecular dynamics (MD) simulations. Compared with the high stress-driven homogeneous nucleation criterion in pure BCC metals, the Zr-V short-range orders in the RHEA facilitate preferential inhomogeneous nucleation at low stress. The local compositional fluctuation not only causes intermittent slipping of screw dislocations by the trapping-detrapping mechanism but also severely reduces the moving rate of edge dislocations. In particular, the initial dislocation nucleation in the RHEA becomes more difficult with the increasing temperature. Based on the competitive mechanism between multiple-element-induced lattice distortion and point-defect-induced lattice distortion, the reason for their excellent retained mechanical properties at high temperatures was revealed. This study would provide theoretical support for the development of RHEAs in high-temperature technological applications.
NSTL