查看更多>>摘要：The evolution of microstructure and mechanical properties of Al-7Si-0.4Mg alloys doped with La/Zr/La+Zr was investigated by experimental characterization and thermodynamic calculation. The combination of growth restriction effect by La-rich intermetallics and inoculation effect by peritectic Zr-rich cores led to the most dramatic grain refining. Furthermore, eutectic silicon was observed to be refined from avg. 9.8 μm in length within original alloy to avg. 5.8, 8.7, and 6.4 μm under the effect of La/Zr/La+Zr additions, respectively. The length reduction in eutectic silicon was attributed to the shrunk growth space caused by grain refinement and the presence of La-rich phases, as well as the impeded effect of several microns La-rich phases distribute directly on the growth front of Si phase. The strength and ductility were both elevated in the alloys at the casting state alloyed with La, Zr, or La+Zr. Particularly, the simultaneous introduction of La+Zr led to the optimal combination properties with a yield strength of 103 ± 3.4 Mpa, an ultimate tensile strength of 189.2 ± 4.6 Mpa, and fracture elongation of 6.1 ± 0.8%. The enhancement of yield strength was related to the strengthening from grain refining and dispersed precipitates. The improved ultimate tensile strength was ascribed to the higher and more stable strain-hardening rate, resulting from the combined influence of refined microstructures (e.g. grain and eutectic Si), as well as the emergence of La-rich and/or Zr-rich intermetallics. The elevation of fracture elongation was intimately correlated with the refining in eutectic silicon, which relieved the nucleation and development of crack along the interface between silicon and Al matrix.
查看更多>>摘要：The etch pit method is used widely to reveal dislocations in GaN via a molten KOH+NaOH solution. To understand the pit formation mechanism better, we performed a statistical analysis of the three-dimensional pit geometry. Particular attention was focused on the slope of the pit facet that forms an angle θ with the {0001} plane. It was found that tanθ is linearly proportional to the apparent pit depth D for a given type of dislocation. Therefore, the slope of the linear fitting (SLF) of tanθ vs. D/t (t is the etch time) could be used to identify the dislocation type and was more reliable than using pit widths. Transmission electron microscopy was used to confirm the results. It is thought that the SLF reflects the configuration of atomic steps at the dislocation core. Our results imply that pit formation is governed by thermodynamic pit nucleation at the dislocation core, followed by kinematic facet development.
查看更多>>摘要：Bi3+ sensitized Gd2O3:Eu3+ phosphors were synthesized by hydrothermal method using polyvinylpyrrolidone as capping agent. As-prepared samples exhibit crystalline hexagonal phase Gd(OH)3. While post annealing at 900 °C, Gd(OH)3 transforms to cubic phase Gd2O3. The lattice substitution by Bi3+ in different symmetry sites, viz. C2 and S2 of Gd2O3 leads to 2 (two) prominent excitation bands related to the 1S0 → 3P1 of Bi3+. Both the excitation bands induce efficient energy transfer to the excited states of Eu3+. In both the cases, the energy transfer efficiency can reach upto ~97%. The energy transfer from the sensitizer (Bi3+) to the activator (Eu3+) occurs mainly through dipole-dipole interactions. The occurrence of energy transfer from Bi3+ to the Eu3+ is corroborated from both the steady state and decay lifetime studies. Color saturation of the red emission when excited in the wavelength range ~330–380 nm is observed ~70–85%. CIE chromaticity reveals the tunability of the color emission by changing the activator concentration.
查看更多>>摘要：The spontaneous crystallization approach was used to synthesize two non-centrosymmetric scandium borate crystal materials, K3ScB6O12 (1) and K6NaSrSc2B15O30 (2), possessing the [B5O10]5? group. Both compounds exhibit wide band gaps of 5.75 and 5.92 eV, respectively. The second harmonic generation (SHG) effects of 1 and 2 are 1.3 and 0.7 times that of the commercial material KH2PO4 (KDP), respectively. According to the Kurtz-Perry approach, 2 demonstrates type-I phase-matchable. First-principles calculations on 2 are done to better understand the link between structure and performance. The calculated results reveal that the discrete arrangement of [B5O10]5? groups and the distorted ScO6 polyhedra in the structure are mainly responsible for the SHG response of 2. Furthermore, since 1 and 2 possess short ultraviolet (UV) cut-off edges, they may be applicable as nonlinear optical (NLO) materials in the UV region.
查看更多>>摘要：Thin film thermocouples can be applied in in-situ temperature measurement. Herein, the flexible In2O3/ITO thin film thermocouples accompanying with the excellent thermoelectric response were prepared by using radio-frequency magnetron sputtering method. A SiO2 buffer layer was accreted between the flexible polyimide substrate and the thermocouples. The effects of the SiO2 buffer layer on morphology, optical transmission, resistances and thermoelectric response of thin film thermocouples were systematically studied. The results show that the resistances of In2O3/ITO thin film thermocouples with SiO2 buffer layer exhibited a consistent trend with the increasing of bending cycles. Under the bending strain of 0.13%, an average Seebeck coefficient was 171.7 μV/°C for the thin film with the SiO2 layer, which was 2.8 times than the film without SiO2 layer. This work presents a great potential for achieving high thermoelectric response of thin film thermocouples, and it also provides an interesting insight of flexibility and bending strain through buffer layer accretion.
查看更多>>摘要：The exploration of new infrared (IR) nonlinear optical (NLO) materials with large second-harmonic generation (SHG) responses and wide band gap (Eg) is an urgent need but challenging. Starting from the superior unit combination strategy and considering the advantages of borates, chalcogenides and Li elements, we have focused our attention on the exploration of IR NLO materials in the Li-based thioborates. Four novel non-centrosymmetric LiBS2 structures, were obtained successfully through crystal structure prediction by analogy and structural optimization based on the thermodynamic and dynamic stability analysis. Among them, LiBS2-I exhibits an ultra-wide band gap Eg = 4.4 eV, moderate SHG response 0.6 × AgGaS2, and suitable birefringence Δn = 0.04 at 1064 nm, which satisfies the good balance between Eg ≥ 3.0 eV and dij ≥ 0.5 × AgGaS2. The role of microscopic units [BS4] in NLO effect was investigated. This work enriches the structural diversity of thioborates and provides a new approach to the exploration of excellent IR NLO materials.
查看更多>>摘要：Compared to the three-dimensional (3D) counterparts, single-layered two-dimensional (2D) perovskites show high stability, high exciton binding energy and structural flexibility that are beneficial for light-emitting diodes (LEDs) applications. Yet, the emission peaks of single-layered 2D perovskites are strongly limited to the blue-green region due to their very strong quantum confined effect, hampering their application. Doping ions has been recognized as a promising way to tune emission wavelengths. In this work, we have prepared Eu3+ doped PEA2PbCl4 perovskites by a hot-injection method. Its Eu3+ emission is not stable, which disappears after exposed in the air due to the coordination of Eu3+ with H2O or O2. By exploiting strong ligands of thenoyltrifluoroacetone (TTA), the H2O or O2 can be replaced, resulting in a rigid coordination environment for Eu3+. Besides, energy level alignment can be modified by the passivation of TTA, leading to effective energy transfer from exciton to Eu3+. In the end, stable red-emitting perovskite is acquired with a photoluminescence quantum yield (PLQY) up to 83%. This work provides new synthetic strategies for the design of high-performance perovskite/lanthanide composites.
查看更多>>摘要：The microstructure and microtexture evolution of a near-alpha titanium alloy Ti-6321 during the post-annealing process after the hot-rolling were investigated. The microstructure of the hot-rolled plate developed differently at distinct annealing temperatures and the macrozone sizes and morphologies changed at the same time. The results showed that the recrystallization process was not fully achieved after hot-rolling and macrozones had formed after the hot-rolling process with its longitudinal direction extending nearly parallel to the rolling direction and exhibited strong transverse basal texture. After post-annealing, the recrystallization, α grain globularization, coarsening as well as the αp→β→αs phase transformation occurred depending on the temperatures, resulting in the decrease of density and size of macrozones and weakening of< 0001 > ||TD texture component. Variant selection and the influence of αp contributed to the texture inheritance, whereas globularization, β grain growth, and new variant formation led to the orientation spread of αs.
查看更多>>摘要：Mn and Cu co-doped perovskite nanocrystal (NCs) thin films with high Mn2+ doping concentration are successfully achieved by a simple one-pot method at room temperature. Structural and compositional analyses manifest that Cu2+ ions can partly replace the Pb2+ ions in the lattice structure and effectively reduce the defect concentration of 2 CsPb(Br/Cl)3 NCs. Steady-state and time-resolved photoluminescence (PL) spectroscopy were employed to characterize the effect of Cu ions doping on the luminescence properties of Mn-doped CsPb(Br/Cl)3 NCs. Mn2+ related PL quantum yields of Mn-doped CsPb(Br/Cl)3 NCs thin films with the Mn/Pb ratios of 7:1 was validly improved from ~34% to ~50% because of the incorporation of Cu2+ ions. Our work provides a low-cost synthesis for Mn-doped perovskite NCs thin films with high emission efficiency in the application of lighting, display and photodetector.
查看更多>>摘要：Barium hexaferrite-polypyrrole (BHF-Ppy) nanoparticles were synthesized by in-situ polymerization of pyrrole monomer in the presence of BHF. BHF was first successfully prepared through the coprecipitation method using barium and iron nitrate as raw materials. The microstructure characterization and performance testing were carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and particles size analyses (PSA) facilities. The experimental results indicate that the diameter of BHF nanoparticles was approximately 50 nm. Polymer-based nanocomposite films (0.23–0.25 mm/230–250 μm) were prepared by dispersing BHF, Ppy, and BHF-Ppy nanoparticles with different wt% and analyzed for DC conductivity and electromagnetic interference (EMI) shielding in two different regions of the electromagnetic spectrum i.e. near-infrared (NIR) (700–2500 nm) and microwave region (0.1–20 GHz). Dielectric properties like dielectric constant and dielectric loss were also suggested the high EMI shielding effectiveness. Less than 1% transmission was observed in the whole NIR region by using high wt% of BHF-Ppy and less than ?50 dB total shielding effectiveness was observed in the whole microwave region (0.1–20 GHz).
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Elsevier