查看更多>>摘要：α-MgAgSb thin films are expected to be compatible with the complementary metal oxide semiconductor (CMOS) technology, and could be used to develop thermoelectric modules integrated to microelectronic devices for energy harvesting. However, bulk studies showed that the presence of secondary phases in addition to α-MgAgSb, such as the metallic phase Ag3Sb, deteriorates the thermoelectric properties. Consequently, understanding phase transformations in Mg-Ag-Sb thin films produced by CMOS-compatible magnetron sputtering is capital for the production of homogeneous α-MgAgSb thin films to be used in energy harvesting thermoelectric modules integrated into microelectronic devices. In this work, different Mg-Ag-Sb films were deposited by magnetron sputtering using either a single alloyed target with the average composition Mg1/3Ag1/3Sb1/3 or using Mg, Ag, Sb co-deposition from three elementary targets. In situ X-ray diffraction measurements were used to investigate the phase transitions in the films, aiming to determine the thermal stability of α-MgAgSb and to investigate the possibility of producing α-MgAgSb films without secondary phases. The results show that the use of the single alloyed target does not allow the production of homogenous α-MgAgSb films. The phase formation sequence observed in the films is different from bulk samples in this case. Co-sputtering of the three elements Mg, Ag, and Sb, allowing the composition of the as-deposited film to be better controlled, confirmed that the Mg1/3Ag1/3Sb1/3 stoichiometry does not allow the production of homogenous α-MgAgSb films. Contrasting with usual belief, the results show that the Ag and Sb compositions of the phases α-MgAgSb and γ-MgAgSb vary during annealing, and the phase transitions α-to-β, β-to-γ, and α-to-γ are not allotropic. These finding are of major importance for the production of the thermoelectric compound α-MgAgSb, and explain the large variations of the α-MgAgSb Seebeck coefficient reported in the literature.
查看更多>>摘要：Combination of multiple structural groups was developed as one effective method for regulating material property and exploring new nonlinear optical (NLO) crystals. For that reason, four Ln3MGeS7 (Y3LiGeS7, Y3Cd0.5GeS7, Gd3Cd0.5GeS7 and Sm3Zn0.5GeS7) crystals with various structural motifs were successfully synthesized and systematically investigated. Note that Y3LiGeS7 and Y3Cd0.5GeS7 were firstly synthesized so far. Performance test shows that Ln3MGeS7 compounds exhibit the variable optical bandgaps (1.62–2.33 eV) and good second harmonic generation (SHG) responses (0.7–1.1 × commercial AgGaS2) with requisite phase-matching behavior, which agree well with the theoretical results (Y3LiGeS7: Δn = 0.058 and d33 = 19.97 pm/V; Y3Cd0.5GeS7: Δn = 0.055 and d33 = 20.6 pm/V) and introduction of MIIB (Zn, Cd) atoms into crystal structure is conducive to enlarge the SHG effect. SHG density and dipole-moment calculations indicate that their SHG effects are originated from the major contribution on LnSn units with moderate effect of GeS4 and MIIBS6 (Zn, Cd) ligands. Therefore, selecting appropriate functional motifs (LnSn and MIIB) into crystal structure can promote the enhancement of NLO property and further realize the rational design of new promising infrared NLO materials.
查看更多>>摘要：Glass containing plasmonic-magnetic nanoparticles have presented striking potential for plasmonic and nonlinear properties. For the first time, we report the synthesis and the magnetic/magneto-optical characterization of plasmonic-magnetic bimetallic Au-Ni nanoparticles (NPs) in heavy metal oxide diamagnetic glasses through co-sputtering technique. The optimum parameters for deposition, diffusion and formation of AuNi NPs were determined and< 50 nm AuNi NPs were synthesized in glass. Compositional and chemical valence states analysis revealed that the NPs is metallic AuNi, oxidization occurred for temperature high than 380 °C. The incorporation of Au-Ni NPs endowed the diamagnetic glass intense SPR peaks and superior optical nonlinearities comparable to that of host and single Au incorporated glasses. The alloy of transition metal Ni contributed to remarkable ferromagnetic character to glasses with characteristic M-H and M-T relations. Giant Verdet constant were obtained for glass and influential reasons were investigated insight of SPR effect, optical energy band gap and magnetization. Glass having 42 nm-AuNi NPs treated at 380 °C for 6 h exhibited huge Verdet constant of 72.66 rad/T m, large third-nonlinear susceptibility of 8.14 × 10?11 esu and strong ferromagnetic moment. This glass will be promising for advanced optical nonlinear and magneto optical applications.
查看更多>>摘要：Heteroatom-doped activated carbons are ideal materials for energy storage devices. In this work, a series of nitrogen/oxygen codoped activated carbons with an inverse opal-like structure derived from cellulose diacetate are successfully synthesized through hydrothermal reaction and subsequent chemical activation during which the fluxing effect of KOH is discovered for the first time. The introduction of nitrogen and intrinsic oxygen (especially carbonyl and quinone groups) contributes to additional pseudocapacitance. The experimental results show that the obtained product delivers 400.3 F·g?1 at a current density of 1 A·g?1 in a three-electrode system and achieves extraordinary capacity retention of 90% after 10,000 charge-discharge cycles at 5 A·g?1. The energy density reaches as high as 8.8 Wh·kg?1 at a power density of 0.25 kW·kg?1 as symmetric supercapacitors, indicating a promising electrode material for high performance supercapacitors. The simple and cost-effective method requires no extra oxidation and excessive urea and thus provides new approaches for the future design of electrode materials.
查看更多>>摘要：Low-temperature operation of reversible solid oxide cells can effectively improve their stable and economical application. However, insufficient catalytic activity of the air electrode is the limiting factor for reversible solid oxide cells. Here, we fabricate a novel Pr0.9Ag0.1Ba0.5Sr0.5Co2O5+δ nanofibers with enhanced electrocatalytic activities via an electrospinning technique and in-situ exsolution. The study confirms the advantage of morphology engineering in enlarging the catalytic interface and reactive sites, and the cells with Pr0.9Ag0.1Ba0.5Sr0.5Co2O5+δ nanofibers air electrode exhibit obviously decreased polarization resistance (0.06 Ω cm2), increased electrolysis current density of 0.65 A cm-2 (50 vol% absolute humidity and 1.5 V), and adequate power density (~ 0.5 W cm-2) at 700 °C. Also, the cell exhibits exceptional reversibility and stability during the long-term test. The enhancement may be assigned to the in-situ exsolution of Ag nanoparticles at Pr0.9Ag0.1Ba0.5Sr0.5Co2O5+δ surface and better interface combination between the air electrode and electrolyte. This work provides an exemplificative study on the favorable nanofibers air electrode for high performance intermediate temperature reversible solid oxide cells.
查看更多>>摘要：One-dimensional metal nanostructures are of great interest for applications in electronic and micromechanical devices, solar cells, sensors, and heterogeneous (photo)catalysts. We describe the multigram preparation method for nanoscopic tungsten fibers (diameter 107 ± 49 nm) for the first time. The material was prepared by needleless electrospinning from an aqueous polyvinyl alcohol and silicotungstic acid solution. A green fibrous composite mat was calcined in air to WO3/SiO2 fibers and further reduced in forming gas at various temperatures (500–1000 °C). The reduction process proceeded from nanofibrous blue tungsten oxide to mixtures of reduced tungsten oxides with metallic tungsten and finally at 800 °C to pure metallic W in the form of polycrystalline fibers. These nanofibers consist of individual tungsten nanoparticles covered and interconnected by amorphous silica. All prepared materials were characterized by the TG-DSC, TG-DTA, SEM, TEM, STEM-EDS, and XRD methods. This optimized fabrication method could be scaled up to supply ample amounts of metallic tungsten nanofibers for future applications.
查看更多>>摘要：15 μm thick Ti-Sapphire coatings were synthesised at room temperature by the plasma electrolytic oxidation (PEO) method for 20 min from the pure aluminium substrate and with the addition of the TiO2 particles in various concentrations in the supporting electrolyte. The coatings are featured by microscopic pores typical for PEO surfaces. The dominant is the alpha phase of alumina with the small presence of the gamma phase. The estimated average crystalline size is 41 nm. Ti is uniformly distributed in these polycrystalline ceramic coatings and does not affect morphology or phase content. Photoluminescence of PEO-created coatings shows typical absorption, excitation, and emission features of Ti-Sapphire with two broad-overlapping excitation bands in the green and blue spectral region due to the Jahn-Teller splitting of the 2Eg level and the Stokes shifted emission centred at 720 nm. 2Eg energy state splitting is equal to 2195 cm?1 and 10 Dq ≈ 19,300 cm?1. The highest emission intensity was observed in the coating prepared with the 0.1 g/L TiO2 powder concentration, i.e. 0.32 at% of incorporated Ti3+. Emission spectra recorded at temperatures ranging from 100 K to 300 K revealed the Mott-Seitz temperature dependence of emission intensity with the 1180 cm?1 activation energy. The fit to the McCumber-Sturge relation gave, for the first time, the value of Debye temperature of 594 K of Al2O3:Ti. Non-contact, luminescence temperature sensing from the temperature-induced changes in the emission bandwidth gave a high sensitivity of 3.2 cm?1 K?1 and 0.19 K temperature resolution. The PEO created Ti-sapphire coatings are a promising multifunctional barrier level – optical temperature sensor material for applications in harsh environments or on large aluminium surfaces. It shows potential to be used as a planar waveguide Ti-Sapphire laser active medium.
查看更多>>摘要：In this work, PdO nanoparticles-decorated ZnO flower-like nanostructures (PdO/ZnO) were synthesized by a one-step facile hydrothermal route and investigated their performance for hydrogen sensing applications. The structural and morphological characterizations were examined by XRD, FESEM, EDS, TEM, and XPS techniques and confirmed the homogenous decoration of PdO nanoparticles on the surface of ZnO flowers. UV-Vis spectroscopy and photoluminescence (PL) spectroscopy were used to investigate the optical characteristics. The ZnO and PdO/ZnO sensors were explored towards different target gases such as hydrogen (H2), carbon monoxide (CO), nitrogen dioxide (NO2), and ethanol. The concentration range of target gases was 2–100 ppm at an operating temperature range of 200–400 °C. It was concluded that PdO/ZnO flowers sensor showed high sensitivity, a speedy response time (20 s), and recovery time (960 s) towards H2 at 350 °C in comparison to the ZnO sensor. In addition, the PdO decorated ZnO flowers-based sensor showed high selectivity towards H2 against CO, NO2, and ethanol. This enhanced gas-sensing performance of the PdO/ZnO sensor has been attributed to the catalytic effect of PdO nanoparticles, and the formation of the PdO-ZnO p-n heterojunction, and their unique flower-like nanostructures. As a result, our research shows that coating PdO on ZnO flowers is an effective technique to improve hydrogen gas sensing performance and can be employed in various applications. The synergist impact of PdO nanoparticles, the arrangement of the PdO-ZnO p-n heterojunction, and their remarkable blossom-like nanostructures were the significant elements for improved gas-detecting execution of PdO/ZnO sensor.
查看更多>>摘要：In this paper, NiS nanoparticles had been successfully loaded on activated carbon (AC) derived from sodium lignosulfonate via hexadecyl trimethyl ammonium bromide assisted hydrothermal method. Due to synergistic effects of AC and NiS nanoparticles, the conductivity of the NiS/AC electrode is significantly improved, and the composite electrode exhibits a high specific capacity (677 C/g at 0.5 A g?1) and excellent rate performance. Moreover, an asymmetric supercapacitor (ASC) device was assembled with the NiS/AC composite as positive electrode and the AC as negative electrode to evaluate the electrochemical performance of NiS/AC composites in practical applications. The ASC device achieves a maximum energy density of 45.6 Wh/kg at a power density of 509.5 W/kg, and excellent cycling stability with 92.6% of capacitance retention after 20,000 cycles. The electrochemical performance suggests that NiS/AC composites have great application prospect as electrode materials for supercapacitors.
查看更多>>摘要：Magnesium hydride is a promising hydrogen storage material and how to improve its sorption kinetics is one of challenges in practical applications. In this paper, a new approach is proposed to catalyze MgH2 with highly dispersed Ni nanoparticles by in-situ hydrogenolysis of nickelocene (NiCp2) in ball milling process. After ball milling under 4 MPa hydrogen atmosphere for 15 h, the MgH2–16.1 wt% NiCp2 sample exhibits a homogeneous morphology where the in-situ formed Ni nanoparticles with size of ~8 nm are highly dispersed in MgH2 matrix. During initial dehydrogenation, Ni would react with MgH2 to form Mg2Ni which inherits the configuration of its high dispersion. In the subsequent hydrogen absorption and desorption cycles, the much fine and highly dispersed Ni-based catalytic phase contributes to the superior hydrogen desorption kinetics of MgH2 with a high-capacity retention rate of ~96% after 50 cycles. This work demonstrates that the in-situ formation of highly dispersed catalytic species is beneficial for improving hydrogen storage properties of MgH2.
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Elsevier