查看更多>>摘要：This article reports exchange bias (EB) and memory effect in nanocrystalline CoCr2O4 with a detailed understanding of the origin of the observed effect. In order to investigate the EB effect in nanocrystalline CoCr2O4, two samples are synthesized with particle sizes 12 and 7 nm via sol-gel route (the second one is embedded in amorphous silica host). For both the samples, despite usual core-shell interaction or ‘surface’ domination, conventional EB effect is observed where the EB field sharply decreases with temperature and vanishes over the spiral ordering temperature (TS) of the samples. A bulk sample of the same composition, with particle size greater than 150 nm, reproducing similar characteristics, rules out the origin of EB due to surface effect. Results indicate that the exchange bias is due to inherent magnetic inhomogeneity: interaction between spiral spin order and collinear ferrimagnetic order below TS. The ac-susceptibility measurement points towards absence of surface glassiness in the sample with 12 nm particle size. However, the sample with particle size 7 nm reveals the characteristics of superspin-glass (SSG), confirmed by magnetic memory effects both in time (t) and temperature (T) dependent magnetization protocols.
查看更多>>摘要：The non-contact thermometry based on fluorescence intensity ratio of phosphors has been extensively investigated owing to its high sensitivity and fast response. However, most of them only use a single mode of upconversion or downconversion emission for temperature sensing and ignore the affection of the humidity. In this work, the Yb/Er ions doped La2Mo3O12 microcrystals with nonhygroscopic property and multimode luminescence have been developed for temperature sensing. The optical thermometer could be based on not only luminescent intensity ratio of upconversion and downconversion, but also average fluorescence decay lifetime. The maximal absolute sensitivity can reach up to 6.2% K?1 and the maximal relative sensitivity is 1.63% K?1. Moreover, the fluorescence emission intensity of the doped La2Mo3O12 microcrystals will not be affected by the humidity compared to some doped molybdate and tungstate. These excellent performances suggest that the La2Mo3O12:Yb/Er microcrystals possess great potential for practical applications in temperature sensing.
查看更多>>摘要：CuBi2O4/Bi2O3 thin film was synthesized on the commercial glass by a spray pyrolysis-calcination method. The monoclinic phase Bi2O3 with dominant (0 2 0) facets was grown on the surface of tetragonal phase CuBi2O4 by the temperature control of spraying process. Photocatalytic activities of the synthesized materials for CO2 reduction were measured in the presence of water vapor under visible light irradiation (λ > 400 nm). The CO, CH4 and O2 yields of the optimal composite film reached 247.62, 119.27 and 418.00 μmol/m2 after 12 h of irradiation. The composite film resisted physical damage and showed good photocatalytic activity in the cycling tests. Moreover, it was found that the types of main products changed with the light intensity and their yields varied with the light wavelength. The exposed (0 2 0) facets efficiently improved the adsorbed ability for H2O molecules. Meanwhile, the hydrophobicity of the film surface ensured that the adsorbed sites of CO2 were unoccupied by abundant H2O molecules. The S-scheme charge transfer mechanism was further confirmed by the interlaced band alignment of the CuBi2O4/Bi2O3 heterostructure and the controlled experiment with different light conditions. The results gained in this report may open up an avenue to design advanced S-scheme heterostructures with suitable transitional-metal oxides for photoreduction CO2 to solar fuels.
查看更多>>摘要：Bismuth tungstate is used as a high potential photocatalytic material, which does not only degrade environmental pollutants but also produces hydrogen for energy use. However, a significant challenge is that the electrochemical potential of its conduction band is more positive, which leads to a weak reduction ability of photogenerated electrons, limiting further improvements in photocatalytic performance and commercial applications. This study proposes a strategy for improving the reduction ability of photogenerated electrons by using Ce/N as a cations/anion to partially replace the W/O position in the Bi2WO6 and to regulate the conduction band potential to move negatively. Meanwhile, N-doped energy level is introduced at the top of a valence band to narrow bandgap width and improve visible light absorption ability, as well as make the photoelectric charge move efficiently. First-principles simulation based on DFT is first used to calculate the energy band structure, density of electronic states and charge density of doped Ce/N materials. Theoretically, doped Ce/N ions can cause the conduction band potential to shift negatively and form an impurity level, which is beneficial to light absorption and electron movement. The degradation efficiency of as-prepared BWCeO-4 and BWCeNO-4 up to 95.5% and 85% was achieved within 90 min under visible light irradiation. Hydrogen production reached 16.89 mmol g?1 and 14.78 mmol g?1 after 4 h reaction time, respectively.
查看更多>>摘要：Randomly oriented ZnO nanowires were grown directly onto alumina substrates having platinum interdigitated screen-printed electrodes via the chemical vapor deposition method using Au as catalyst. Three different Au film thicknesses (i.e., 3, 6 or 12 nm) were used in the growth of nanowires, and their gas sensing properties were studied for ethanol and NO2 as reducing and oxidizing species, respectively. ZnO nanowires grown employing the 6 nm thick layers were the less defective and showed the most stable, repeatable gas sensing properties. Despite ZnO nanowires grown employing the thickest Au layers reached the highest responses under dry conditions, ZnO nanowires grown using the thinnest Au film were more resilient at detecting NO2 in the presence of ambient moisture. The gas sensing results are discussed in light of the defects and the presence of Au impurities in the ZnO nanowires, as revealed by the characterization techniques used, such as X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. Promising results were obtained by the implementation of ZnO NWs directly grown over alumina substrates for the detection of ethanol and NO2, substantially ameliorating our previously reported results.
查看更多>>摘要：To thoroughly understand the damage and fracture behavior of SLM-fabricated Ti6Al4V alloy, a number of tensile, compressive and torsional experiments covering various stress states were conducted with different types of the specimens. The effects of build directions (0°, 45°, 90°) and post heat treatments (annealing and solution-aging) on the behavior were also studied. Metallographic tests were performed to draw out the connection between the material microstructures and mechanical performance, and fractographic analyses were carried out to elucidate the fracture modes and failure mechanisms. Compared with solution-aged material, the annealed material shows higher strength because of its smaller grain sizes of α + β duplex microstructure. While the solution-aged material behaves more ductile than annealed one owing to the larger dislocation slip distance in β phase matrix and the coordinating role of primary equiaxed α phases. The similarity of the microstructures under different build directions accounts for the insignificant anisotropy of the mechanical performance. Furthermore, a 3D fracture locus of SLM-fabricated Ti6Al4V alloy was constructed in the space of equivalent plastic strain at fracture, average stress triaxiality and the Lode angle parameter.
查看更多>>摘要：Ultra-wide bandgap β-Ga2O3 photodiodes have received great attention due to transparent solar-blind deep ultraviolet photodetectors. We demonstrated an all oxide-based single-crystal β-Ga2O3 photodiode incorporated with transparent conductive InZnSnO and InSnO as Schottky and Ohmic contacts, respectively. High work function and low resistivity of InZnSnO allow for clear rectifying characteristics with a low dark current (<0.1 nA) of up to ?100 V of reverse bias. The Schottky barrier height and junction defects at the Schottky interface were modified using post-annealing treatment, thereby influencing the deep ultraviolet photoresponse. The responsivity of the annealed device was 9.6 mA/W, decreasing the Schottky barrier height engineering, while the photo responding speed was degraded and caused a persistent photocurrent effect due to the generation of defect states.
查看更多>>摘要：A variable-rate non-isothermal aging (NIA) process that has two-stage heating and cooling procedures was proposed for a ternary Al-Zn-Mg aluminum alloy aiming to obtain the combination of high strength and excellent corrosion resistance. The mechanical properties, susceptibilities to the stress corrosion cracking (SCC), intergranular corrosion (IGC) and exfoliation corrosion (EXCO), as well as microstructural characteristics of the variable-rate NIA processed materials were investigated. They were compared with that produced by conventional constant rate NIA and isothermal aging processes (T6 and T73 temper). The results show that the new variable-rate NIA process which has different heating /cooling rates in different temperature ranges may be the solution to obtain much higher strength and excellent corrosion resistance. A much higher percentage of fully grown but not coarsened precipitates were obtained within the grains and a discontinuous distribution of GBPs was obtained on grain boundaries. The alloys produced by the new variable-rate NIA process achieved a 5–7 % higher strength than the conventional T6 temper and a higher corrosion resistance than T73 temper. The possible causes for the improvement of strength and corrosion resistance were discussed on the basis of the microstructural evolution.
查看更多>>摘要：We experimentally investigate the long-term atmospheric durability of thermochromic vanadium oxide (VOX) films. The VOX films were deposited on glass substrates by reactive direct current magnetron sputtering and were then in-situ annealed at the preparation temperature ≤350 °C. The X-ray photoelectron spectroscopy (XPS) was applied to investigate the surface compositions of the natural aged films, while the optical properties of the films were characterized by the spectrophotometer and spectroscopic ellipsometry. The XPS results reveal that the oxygen-deficient VOX (X < 2.5) components possessing remarkable chemical changes is preferred to react with the O2 and H2O in the air and become high oxidation state compounds. However, it is worth to note that the optical properties of the films shows extra-low variation performance (e.g. linear increasing rate of transmittance ~0.00448% per day @ λ = 600 nm). The aging mechanism of the VOX films in air was interpreted in terms of the interface aging and the diffusion-reaction aging on basis of the above experimental results. This study would provide valuable experience of the natural aging of VOX films.
NSTL
Elsevier