查看更多>>摘要：Spectroscopic (UV–vis and XPS) magnetic and electrical properties of the Ca2+ doped SmCrO3 system were phenomenologically investigated. The Cr3+, Cr5+, and Cr6+ species were identified by XPS spectroscopy in Sm1?xCaxCrO3 (0 ≤ x ≤ 0.20). Rietveld analyses of the X-ray diffraction data reveal a smooth decrease in the cel‘l parameters assigned to the Cr6+ formation as a function of the Ca2+ content. Diffuse reflectance spectroscopy showed that the wider optical bandgap of the system corresponds to a charge transfer process, and it disappears for x ≥ 0.1, showing t2 g-eg electronic gaps. The electrical measurements were fitted in two temperature ranges; for low temperatures (85–150 K), a 3D variable-range hopping mechanism seems to prevail, while for the 150–300 K range, the electrical behavior is well represented by the small-polarons conduction mechanism. Magnetic properties of Sm1?xCaxCrO3 were highly sensitive to the Ca2+ content, and the TN values varied from 192 to 151 K for x = 0 and x = 0.20, respectively; TRS varied from 34 to 9 K for the same x values. Isothermal magnetization curves at 5 K suggest that, as a function of the Ca2+ content, the Γ4 ferromagnetic phase remains for x ≥ 0.04; while for x = 0 and x = 0.02, the Γ2 ferromagnetic phase is the only one observed.
查看更多>>摘要：Successful applications of a topological insulator (TI) in spintronics require its bandgap to be wider then in a typical TI and the energy position of the Dirac point in the dispersion relations to be away from the valence and conduction bands. In this study we grew Bi1.1Sb0.9Te2S crystals and examined their elemental composition, structural, optical and electronic properties as well as the electronic band structure. The high structural quality of the grown crystals was established by X-ray diffraction and Raman spectroscopy. Angular resolved photoelectron spectroscopy demonstrated a near parabolic character of the valence and conduction bands and a direct bandgap of 0.36 eV. The dispersion relations also revealed a Dirac cone, confirming the topological insulator nature of this material, with the position of the Dirac point being 100 meV above the valence band maximum. Far infrared reflectivity spectra revealed a plasma edge and two phonon dips. Fitting these spectra with theoretical functions based on the Drude-Lorentz model allows determination of the high frequency dielectric constant (41.3), plasma frequency (936 cm?1) and the frequencies of two infrared phonons (177.7 cm?1 and 77.4 cm?1).
查看更多>>摘要：In this work, we report the systematic experimental synthesis and characterization of rare earth Erbium metal incorporated orthoferrite (EOF) nanoparticles (NPs) via microwave-assisted technique. The instrument micro-oven was used to induce exothermic heating inside the sample which causes the formation of ErFeO3 nano-crystallites. The unit cell structure of Erbium substituted orthoferrite nano-crystallite is studied by using experimental results and computational techniques by simulating the orthorhombic phase. Crystal lattice structure and its direct and reciprocal parameters are analysed by performing the Rietveld refinement process on the Powder X-ray diffraction pattern (P-XRD) data which confirms the fabricated unit cell structure belongs to the orthorhombic-cubic phase (spacegroup: Pbnm) with slightly induced distortion in bond distance between atoms. From FTIR fingerprint region of metal oxides, the vibrational frequency of harmonically oscillating Er-O groups in ErFeO3 unit cells was observed at (414 and 420 cm?1) and this value is consistent with the theoretical vibrational frequencies of Er-O (424.0410 and 426.5122 cm?1) calculated based on the Hooks law by considering the Er-O groups as a harmonic system. Similarly, the observed and calculated vibrational frequencies of Fe-O groups are found at (536, 570 and 576 cm?1) and (530.2621, 531.4341 and 549.7296 cm-1) respectively. The band gap of the ErFeO3 is found to be 2.1 eV. Weak Ferromagnetic property is observed in MH plot for the synthesized EOF nanoparticles due to formation of lower bond angle of Fe3+-O-Fe3+ sublattice with 140.5782° and 147.6881°. SEM image of ErFeO3 is confirmed the spherically distributed nano-crystallites with size ranging from 62 to 166 nm. In this research, Match (v3) and VESTA open-source programs are used for the Rietveld refinement process and to calculate bond distance between atoms in the unit cell.
查看更多>>摘要：In this work, FeCoNiCrMo high-entropy (HEA) coating and CeO2/FeCoNiCrMo composite coating were successfully prepared on the surface of TC4 alloy by laser cladding technology. The macromorphology, microhardness and corrosion resistance of FeCoNiCrMo coating with rare earth oxides CeO2 were characterized in detail. The addition of CeO2 powders reduced the crack sensitivity of HEA coating, and CeO2 did not change the phase composition of the coating (BCC phase). SEM analysis revealed that CeO2 was mainly distributed on the grain boundary, which refined the grain and improved the strength and toughness of the coating. Owing to the solution strengthening and dispersion strengthening effects of HEA coatings, the microhardness of HEA coating was enhanced by 2.7 times compared with TC4 substrate. In 3.5% NaCl solution, there were corrosion products generating on TC4 surface, while the corrosion form of HEA coating was pitting corrosion. After adding CeO2 powder, the refined grain structure formed higher density and more stable passive film, which inhibited pitting. Compared with TC4 alloy, HEA coating had lower corrosion current density and higher polarization impedance, which proved that FeCoNiCrMo coating could improve the corrosion resistance of TC4 alloy.
查看更多>>摘要：UVA radiation can survive from the absorption of atmospheric layer and reaches the terrestrial surface, which is harmful to human eyes, blood vessels, and elastic fibers. It is meaningful to detect the UVA radiation precisely. A sensitive, high-detectivity and self-powered UVA detector based on polycrystalline CH3NH3PbCl3/amorphous Ga2O3 hybrid structure is presented in this work. Under zero bias, the rise/decay time of the photodetector are 56/67 ms, and the detectivity reaches up to 5.4 × 1010 Jones. The performance is even superior to most of the reported devices based on CH3NH3PbCl3 single crystal. The heterojunction between amorphous Ga2O3 and CH3NH3PbCl3 accelerates the separation of photon-generated carrier and effectively reduces the recombination. In addition, the high resistivity and low surface roughness of the amorphous Ga2O3 layer also contribute to the improvement of device parameters. This study offers new insights to improve the polycrystalline MAPbCl3 devices by ultra-wide bandgap amorphous semiconductors.
查看更多>>摘要：Inspired by the rich physical properties of thermoelectric materials, we have investigated the electrical transport, vibrational, and structural properties of efficient thermoelectric material Cu3Sb0.98Al0.02Se4 under pressure up to 40.1 GPa. At a critical pressure of 8.5 GPa, a superconducting phase sets in and persists in the pressure range studied. A superconducting dome in the temperature-pressure phase diagram of Cu3Sb0.98Al0.02Se4 was observed. Meanwhile, pressure-induced structural transition from its initial phase to disorder body-centered cubic structure in Cu3Sb0.98Al0.02Se4 has been verified by the X-ray diffraction and Raman scattering measurements. Interestingly, the onset of superconductivity coincides with the structural transition, accompanied with the reduction of volume. The superconducting phase was observed in the ultimate formation of the Cu–Sb–Al–Se alloy and was determined to be Im-3m. Based on Hall coefficient measurements, we evaluated the carrier concentration of Cu3Sb0.98Al0.02Se4, which shows a dramatic increase in the superconducting state. These results suggest that the novel superconductor is realized through the charge transfers and the first-order structural transformation.
查看更多>>摘要：The Mo-10Si-(0, 5, 10, 15)B (at.%) alloys located in Moss (Mo solid solution) +Mo3Si +T2 (Mo5SiB2) region were prepared by arc melting. The effect of B content on the microstructure, microhardness, fracture toughness and oxidation resistance of the alloys was studied. In the Mo-10Si alloy, there are primary Moss and peritectic Mo3Si phases. With the addition of B, (Moss + T2) binary and (Moss + T2 + Mo3Si) ternary eutectics emerge in Mo-10Si-(5, 10)B alloys. For Mo-10Si-15B alloy, primary Moss disappears and the microstructure is only composed of binary and ternary eutectics. With the increase of B content, the proportion and grain size of Moss decrease. The microhardness of alloys increases with the increase of B content due to the increasing intermetallics. The fracture toughness of alloys decreases obviously in single-edge notched three-point bending testing (SENB) and the fracture mode transforms from transgranular fracture to intergranular fracture because of the refinement of Moss. In the high-temperature oxidation test at 1250 °C, the oxidation weight loss of the alloys decreases with the addition of B due to the densification of the borosilicate layer.
查看更多>>摘要：Optical thermometers are of great interest due to their non-contact, high-sensitivity and fast measurement characteristics. In this work, a series of dual-center Bi1.96?xMoO6: 0.02Er3+, 0.02Tm3+, xYb3+ (x = 0.10–0.35) upconverting materials were prepared by a sol-gel synthesis method. Upon 975 nm excitation, the prepared materials exhibit bright color-tunable (from yellow to orange) upconversion (UC) emissions, as the Yb3+ content increases. The thermometric properties of the synthesized materials associated with different thermally-coupled and non-thermally coupled levels of Tm3+ and Er3+ were systematically investigated. Based on the temperature-dependent emissions originating from the non-thermally coupled levels of Tm3+ (3F2,3) and Er3+ (4F9/2), i.e., their band intensity ratios 700/670 nm, the developed optical thermometers were found to exhibit an exceptional relative thermal sensitivity (Sr), up to 5.90% K?1 at 293 K. Importantly, in the whole T-range of 293–623 K, the Sr values are larger than 2% K?1. Furthermore, it is revealed that the position of the Tm3+ emission band, centered around 800 nm is highly dependent on temperature, and, so, it can be utilized as a second thermometric parameter, which is important for a multi-parameter temperature sensing in the T-range of 293–623 K. These results suggest that Er3+/Tm3+/Yb3+-doped Bi2MoO6 materials are promising candidates for ultra-sensitive, dual mode optical thermometers and safety sign applications.
查看更多>>摘要：Creating craters and oxygen vacancies in WO3 nanoflakes with a simple in-situ strategy was carried out by taking WO3/W mesh as cathode and conducting electrochemical reduction at ? 3 V in acid solution. Because of the special chessboard-like arrangement of WO6 octahedra, both H+ and electrons driven by the electric field migrate into WO3, and H+ ions turn into H2 there. The implanted H2 microbubbles release from WO3 lattice by breaking the W–O bonds, the anisotropy of the elastic forces when H2 microbubbles diffuse outward boosts the exfoliation of WO3. Consequently, many craters accompanied with oxygen vacancies (OVs) are manufactured in WO3 nanoflakes, which work as active centers for attracting O2 from air and help to increase the conductivity of WO3. As OVs enable WO3 to become sensitive to lights, abundant reactive oxygen species (ROS) including ?O2-, ?OH, 1O2 are generated, rendering an oxidation-governing degradation of florfenicol (FLO) molecules. When treating water contaminated with 4 mg/L FLO, a perfect degradation efficiency, 93.7%, was achieved under irradiation at 1.2 V with significantly minimizing the ecotoxicity of the chemicals from FLO degradation. This work provides a comprehensive elucidation on creating OVs in WO3 by electrochemical approach with shedding light on the oxidation mechanism in FLO detoxification.
查看更多>>摘要：The behavior of phosphorus during the solidification of the Si-Fe-P ternary alloy melt used in purification of MG-Si was investigated using thermodynamic calculations and design of Si-Fe-P alloy materials with specific composition. It was found that when the concentration of Fe in the liquid phase (LFe) is less than 23 wt%, Fe can promote the decomposition of SiP and the solid solution of P in primary Si, basing on positive activity interaction between Fe-P. After LFe exceeds 23 wt%, Fe will attract P to form clusters and enrich in unsolidified liquid phase or Fe3Si7 phase during the primary crystallization of Si and the eutectic of Si and Fe3Si7(A). Then, the eutectic of Fe3Si7(B) and Si4P4Fe ends the solidification of the alloy melt. These characteristic behaviors lead to the distribution coefficient of P between the silicon matrix and A-Fe3Si7 reaching 0.4868, limiting the effectiveness of P removal from MG-Si by Si-Fe alloy refining. Experiments on in-situ etching and acid leaching in different acid agents showed that HCl+HF and Aqua regia were the optimal acid leaching systems for the removal of P enrichment in Fe3Si7 and Si4P4Fe, respectively.
NSTL
Elsevier