查看更多>>摘要：The development of high energy density Li-O_2 batteries is restricted by the sluggish kinetics of both the oxygen reduction reaction and the oxygen evolution reaction, and developing an efficient cathode catalyst is the key to resolving this issue. In present study, interconnected honeycomb-like NiCo_2O_4 nanoflakes are synthesized by facile electrochemical deposition on carbon cloth (CC) and subsequent heat treatment. Compared with NiO and Co_3O_4, suitably sized NiCo_2O_4 nanoflakes benefit from a vital synergistic effect of components Co and Ni and are expected to show superior OER/ORR performance. The presence of redox couples Co~(3+)/Co~(2+) and Ni~(2+)/Ni~(3+) and abundant oxygen vacancies in NiCo_2O_4 allow Li-O_2 batteries deliver satisfactory cycle durability and high discharge/recharge capacities. Li-O_2 batteries that use the NiCo_2O_4/CC cathodes exhibit high specific discharge capacities of 8388 mA h g~(-1) and 5238 mA h g~(-1) at 200 mA g~(-1) and 400 mA g~(-1) respectively, and deliver a long lifetime of 102 cycles with a capacity limit of 500 mA h g~(-1) at 340 mA g~(-1) thereby suggesting that honeycomb-like NiCo_2O_4 nanoflakes are a promising cathode catalyst.
查看更多>>摘要：Recently, sustainable energy harvesting technologies have received much attention for powering the internet of things architecture. Triboelectric nanogenerators (TENGs) have been regarded as the most promising energy harvesting technology because they can generate a large amount of electrical energy even with very weak mechanical energy and very simple structures. Although there has been much investigation, TENG devices continue to be associated with insufficient levels of converted electrical power. In this study, we report the enhancement of TENG performance outputs based on polyvinylidene fluoride (PVDF)/fuIl-erene (C_(60)) composite nanofibers (NFs). Structural and chemical investigations show that C_(60) is uniformly incorporated into PVDF NFs with C_(60) content levels of less than 0.3 mg. PVDF/C_(60) composite NFs exhibit a consistent p-phase ratio regardless of the C_(60) content. Here, as the C_(60) content was increased from 0 to 0.2 mg, the maximum output power of the PVDF/C_(60) composite NF-based TENG devices increased from 129 to 282 μW, while it decreased to 147 μW with further addition of C_(60) beyond 0.4 mg. The enhanced TENG performance realized with an increase in the C_(60) content originated from the increased trap charge ability and the high electronegativity caused by the incorporated C_(60) in the PVDF matrix. The output power from a PVDF/C_(60) composite NF-based TENG device was sufficient to operate an eco-friendly display device.
Pravin S. PawarRaju NandiKrishnaRao Eswar Neerugatti
10页
查看更多>>摘要：The binary chalcogenide material antimony sulfide (Sb_2S_3) has attracted significant attention as a potential absorber material for photovoltaics (PVs) owing to its suitable bandgap of -1.7 eV and other unique properties. However, only a few substrate-configured Sb_2S_3 thin-film solar cells (TFSCs) have been reported, and they demonstrated an extremely low power conversion efficiency (PCE, η < 2.5%) owing to the unfavorable (hk0) orientation of Sb_2S_3. In most studies, Sb_2S_3 absorber layers were grown through physical vapor deposition or high-vacuum methods. By contrast, we used a facile hydrothermal approach to deposit Sb_2S_3 thin films on molybdenum and investigated the effect of post-deposition annealing on the structure, orientation, and morphology of Sb_2S_3 thin films. Annealing at temperatures ranging from 0° to 350°C transformed the Sb_2S_3 thin films from nearly amorphous to polycrystalline with large, horizontally aligned plate-like grains. All the annealed Sb_2S_3 thin films were confirmed to have a preferred orientation along the (hkO) crystal direction. The fabricated substrate-configured TFSCs with SLG/Mo/Sb_2S_3/CdS/i-ZnO/Al-doped ZnO/Al configuration exhibited the highest PCE of -1.0%. Further, over 95% of this initial efficiency was maintained after 90 days. We also addressed the underlying reasons for the low efficiency of Sb_2S_3 TFSCs to provide a pathway for improving the device performance in the future.
查看更多>>摘要：The present study reports the evolution of microstructure and magnetic properties of Cu_2MnAl_(1-x)Gax Heusler alloys. The L2_1 phase, which remained stable up to a Ga substitution of x = 0.3, transformed into mixed phases, i.e., hexagonal close packed (HCP) and complex cubic structure (CCS) on further addition of Ga. The non-monotonic increase in the lattice constant indicates that some amount of Ga retains its monovalent state. The magnetic phase showed a transition from ferromagnetic to paramagnetic state with increasing Ga concentration. The re-entrant temperature (T_R) decreased from 8.2 K to 5.2 K as Ga content increased from 5 at% to 10 at%. The strength of magnetic exchange-coupling also reduced with an increase in Ga content. Gaussian process regression (GPR) was used to estimate the lattice parameter using the ionic radii and Pauling electronegativity of the constituents. The modeling approach showed high accuracy and stability, providing new insights into future alloy development.
查看更多>>摘要：Trimethylamine (TMA), which mainly emanates from decaying fish, is an important freshness indicator of seafood. In this work, a TiO_2-NiFe_2O_4 heterojunction was successfully synthesized for TMA detection using a simple and efficient hydrothermal method. The materials were characterized using X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. The TiO_2-NiFe_2O_4-based sensor exhibited the largest response (12) to 10 ppm of TMA at 307 °C The response was further improved under white-light irradiation, increasing from 2.5 to 4.5 as the TMA concentration approached 3 ppm. The enhanced gas-sensing performance of the TiO_2-NiFe_2O_4 sensor under light irradiation was then explored by density functional theory (DFT) with an optical carrier. We believe that the developed strategy improves the gas-sensing ability for TMA detection and can potentially be used in gas sensors.
查看更多>>摘要：From the XRD results, it is found that the studied La_(0.5)Ca_(0.2)Ag_(0.3)MnO_3 compound crystallizes in the or-thorhombic structure with Pnma space group. Electrical conductivity of La_(0.5)Ca_(0.2)Ag_(0.3)MnO_3 compound is investigated from 80 K to 480 K in the frequency range [40 Hz-6 × 10~5 Hz]. Several conduction models are used to identify the appropriate mechanisms governing the transport properties in the studied compound. The Overlapping-Large- Polaron Tunneling and the Correlated Barrier Hopping conduction processes are used to clarify the sub-linear dispersive regions in the DJPL/JPL frequency range. In these regions, the conductivity is examined according to double and single Jonscher power laws. At lower temperatures and for the second frequency range, the spectra reveal Superlinear Power-Law behavior. Beyond T = 280 K, this phenomenon is disappeared and replaced by Nearly Constant Loss behavior. At higher frequencies, the conductivity spectra exhibit a high frequency plateau. For the DC regime, the transport properties are governed by thermally activated Small Polaron Hopping conduction process at elevated temperatures. The Variable Range Hopping conduction mechanism is the dominant process in the intermediate temperature range. Thus, the cationic disorder plays a major role in the transport of charge carriers at low temperatures. Likewise, the investigated compound exhibits semi-conductor behavior over the explored temperature region. The deduced hopping energy is sensitive to the frequency parameter. At high frequencies, a signature of a metal-semiconductor transition is observed at 260 K. The magnetic investigation shows that the sample reveals a paramagnetic-ferromagnetic phase transition at 260 K.
Tomas MurauskasVirgaudas KubiliusMartynas Talaikis
8页
查看更多>>摘要：La:BaSnO_3 has recently emerged as an outstanding perovskite oxide material due to its high electron mobility. To-date, lower electron mobility in thin films compared to the single-crystal are discussed in terms of the presence of dislocations, nearly neglecting the role of cation nonstoichiometry. However, by controlling Sn/Ba compositional ratio, we demonstrate the significance of stoichiometry and resulting point defects on microstructure, morphology, electrical properties, and Raman defect modes in epitaxial La:BaSnO_3 films. A narrow compositional window is demonstrated to yield high mobility and smooth morphology in La:BaSnO_3 thin films using the metalorganic chemical vapor deposition. The room temperature electron mobility of 121 cm~2V~(-1)s~(-1) and 85 cm~2V~(-1)s~(-1) was achieved on SrTiO_3 and MgO substrates, respectively. Correlation between the lowering of the A_1 g soft mode near 140 cm~(1) frequency and increase in the carrier mobility is demonstrated by Raman spectroscopy analysis. It was suggested that the position of this soft mode might be employed as a marker band for probing the electrical properties of La-doped BaSnO_3 perovskites.
查看更多>>摘要：In this work, a series of (l-x)MgAl_2O_4-xMg_2TiO_4 (expressed as (l-x)MA- xMT) (0.0 < x < 0.9) ceramics were successfully prepared via a solid-state reaction, and the effect of Mg_2TiO_4 content on the phase compositions, microstructures and microwave dielectric properties of MgAl_2O_4 ceramics have been investigated. The MgAl_2O_4 could form a solid solution with Mg_2TiO_4, and the grain size of the (l-x)MA-xMT ceramics gradually increased with the increase of sintering temperature. The dielectric constants (ε_r) of (l-x)MA-xMT ceramics steadily increased with the increase of Mg_2TiO_4 content. The ε_r values were mainly affected by secondary phase and dielectric polarizability. The quality factor (Qf) of (l-x)MA-xMT ceramics was closely related to the relative density, secondary phase, cation vacancies and Ti valence; whereas the temperature coefficient of resonance frequency (τ_f) highly depended on the Al-site bond strength. For the sample at x = 0.9, the 0.1MA-0.9MT ceramics sintered at 1350 °C for 4 h exhibited the optimized microwave dielectric properties: ε_r = 12.36, Qf = 236,600 GHz and τ_f = -61 ppm/°C.
查看更多>>摘要：The authors regret that the layer thickness and hatch spacing in Table 2 should be 0.05 and 0.12 mm respectively in the original paper. Meanwhile, an incorrect version of Fig. 7 was used. The correct version is exhibited below.
查看更多>>摘要：Laser powder bed fusion (LPBF) is a robust metal additive manufacturing technology which can produce precise parts with high complexity and freedom. In a recent work by the authors, a significant number of microstructural defects was observed on the surface of the LPBF-fabricated parts, which could account for the poor tensile strength of the parts. It was revealed that the regions near the surface of the part are more affected by the convection heat transfer mode compared to the areas located away from the surface. In this study, for the first time, a novel technique is proposed to address the issue of microstructure inconsistency in the LPBF-fabricated Inconel 718 parts. This approach is based on the design and fabrication of a border surrounding the main part during the LPBF fabrication. It is hypothesized that such a border, if designed appropriately, would mitigate the undesirable convention heat transfer mode in the areas near the surface of the LPBF-fabricated parts and may result in microstructure homogeneity. To this aim, cubic samples surrounded by borders at two different gap distances of 0.5 mm and 2 mm were fabricated to control the rate of heat dissipation and thus control the microstructure along the cross section and reduce surface defects such as microcracks and porosities. Reference cubic samples were fabricated without borders to compare them with the samples fabricated with borders. Scanning electron microscope (SEM) and optical microscope were used to study the changes in microstructure, X-ray diffraction (XRD) was used to perform compositional analysis, and Vickers hardness test was conducted to study the hardness properties. For the sample fabricated with a smaller gap, the smaller melt pools overlapped to form deeper melt pools and led to the formation of more columnar grain structures elongated parallel to the build direction. The fabrication of borders around the sample also helped in controlling the heat transfer of the sample and thus reducing the surface porosities and defects. A higher level of secondary strengthening phases (γ, γ") was seen to precipitate into the matrix for the samples fabricated with borders. Vickers hardness values were higher for the samples fabricated with borders than that of the reference sample.
NSTL
Elsevier