The double perovskite family, A2MIMIIIX6, is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH3NH3PbI3. Given the generally large indirect ...band gap within most known double perovskites, band‐gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs2AgBiBr6 as host, band‐gap engineering through alloying of InIII/SbIII has been demonstrated in the current work. Cs2Ag(Bi1−xMx)Br6 (M=In, Sb) accommodates up to 75 % InIII with increased band gap, and up to 37.5 % SbIII with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs2Ag(Bi0.625Sb0.375)Br6. Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three‐metal systems are also assessed.
Unleaded: The substituted double perovskites, Cs2Ag(Bi1−xInx)Br6 (x=0, 0.25, 0.5, and 0.75) and Cs2Ag(Bi1−xSbx)Br6 (x=0, 0.125, and 0.375), were successfully synthesized. The band gap can be tuned from 1.86 eV to 2.27 eV, associated with broad photoluminescence from visible to near‐infrared. Band structure calculations provide insight into the band gap engineering in these alloys, and environmental stability was assessed over a two‐month period.
Achieving efficient fuel-air mixing is a crucial problem for the design of scramjet engines. Due to the very short residence time of the fuel within the scramjet combustor for typical flight ...conditions, an efficient injection strategy with high penetration depth and rapid mixing is required. For this reason, many mixing augmentation devices have been proposed and investigated, namely wall injection, struts, ramps, cavities, vortex generators and new configurations developed in China. In this survey, their mixing augmentation mechanisms are analyzed and the numerical and experimental studies are described which have been performed for the assessment of their mixing effectiveness. Some novel insights are provided to further the development of large-scale scramjet engines at increased flight Mach number. The need for additional research based on improved numerical approaches and experimental facilities is stressed.
Recently, CuI‐ and AgI‐based halide double perovskites have been proposed as promising candidates for overcoming the toxicity and instability issues inherent within the emerging Pb‐based halide ...perovskite absorbers. However, up to date, only AgI‐based halide double perovskites have been experimentally synthesized; there are no reports on successful synthesis of CuI‐based analogues. Here we show that, owing to the much higher energy level for the Cu 3d10 orbitals than for the Ag 4d10 orbitals, CuI atoms energetically favor 4‐fold coordination, forming CuX4 tetrahedra (X=halogen), but not 6‐fold coordination as required for CuX6 octahedra. In contrast, AgI atoms can have both 6‐ and 4‐fold coordinations. Our density functional theory calculations reveal that the synthesis of CuI halide double perovskites may instead lead to non‐perovskites containing CuX4 tetrahedra, as confirmed by our material synthesis efforts.
Tetrahedra preferred: Owing to the high‐energy level for the Cu 3d10 orbitals, CuI atoms energetically do not favor the 6‐fold coordination required for CuX6 octahedra. DFT and experimental studies reveal that the CuI halide double perovskites are thermodynamically unstable against decomposition into products containing CuX4 tetrahedra.
Leveraging the motion and force of individual molecular motors in a controlled manner to perform macroscopic tasks can provide substantial benefits to many applications, including robotics. ...Nonetheless, although millimetre-scale movement has been demonstrated with synthetic and biological molecular motors, their efficient integration into engineered systems that perform macroscopic tasks remains challenging. Here, we describe an active network capable of macroscopic actuation that is hierarchically assembled from an engineered kinesin, a biomolecular motor, and microtubules, resembling the contractile units in muscles. These contracting materials can be formed in desired areas using patterned ultraviolet illumination, allowing their incorporation into mechanically engineered systems, being also compatible with printing technologies. Due to the designed filamentous assembly of kinesins, the generated forces reach the micronewton range, enabling actuation of millimetre-scale mechanical components. These properties may be useful for the fabrication of soft robotic systems with advanced functionalities.
The dual-mode scramjet combustor is a promising candidate for the combined cycle engine of the hypersonic airplane, and the flame propagation and stabilization process in the dual-mode scramjet ...combustor has a great impact on its performance improvement. In this survey, the research progress on the flame propagation and stabilization in the dual-mode scramjet combustor is reviewed and summarized, and its main focus is on the flame stabilization mode, especially for the mode transition. The flame stabilization process in the dual-mode scramjet combustor is summarized from three aspects, namely the combustion mode classification, the mode transition and the vitiation effect. The obtained results show that the operational conditions and the geometric parameters both have a great impact on the flame propagation and stabilization process in the dual-mode scramjet combustor, and there exist strong interactions between the geometric parameters, as well as the operational conditions. This is a multiobjective design optimization problem, and the optimal operational conditions, as well as the optimal geometric parameters, should be obtained by the optimization algorithm based on the surrogate model with high fidelity.
Recently, there has been substantial interest in developing double-B-cation halide perovskites, which hold the potential to overcome the toxicity and instability issues inherent within emerging lead ...halide-based solar absorber materials. Among all double perovskites investigated, In(I)-based Cs2InBiCl6 and Cs2InSbCl6 have been proposed as promising thin-film photovoltaic absorber candidates, with computational examination predicting suitable materials properties, including direct bandgap and small effective masses for both electrons and holes. In this study, we report the intrinsic instability of Cs2In(I)M(III)X6 (M = Bi, Sb; X = halogen) double perovskites by a combination of density functional theory and experimental study. Our results suggest that the In(I)-based double perovskites are unstable against oxidation into In(III)-based compounds. Further, the results show the need to consider reduction–oxidation (redox) chemistry when predicting stability of new prospective electronic materials, especially when less common oxidation states are involved.
AbstractThe surface roughness prior to adhesive bonding plays an important role in enhancing the durability of composite materials. To obtain deep insight into the effect of aggregate surface ...roughness on the interfacial properties of the asphalt–aggregate system, molecular dynamics simulations were carried out. Different surface nanostructure patterns, including groove, grid, and pillar, were generated with predefined roughness ratios in both acidic mineral (quartz) and weak alkali mineral (calcite) models. The influences of surface nanostructure on interfacial interaction energy, tensile bond strength, and the interlocking effect were investigated. In general, the van der Waals energy dominates the interaction energy between asphalt and aggregate surfaces at a low roughness ratio, whereas electrostatic interaction dominates the interaction energy in surfaces at a high roughness ratio because of the unsaturated atoms introduced by the surface nanostructure. Moreover, the presence of surface nanostructures results in the adsorption of more asphalt chains, strengthening the interlocking effect. By increasing surface roughness, the interfacial failure mode under tensile stress gradually transfers from adhesive failure to cohesive failure. In light of the aforementioned observation, a schematic illustration of the bond strength along with surface roughness was obtained.
AbstractUnderstanding the diffusion of moisture in asphaltic materials is crucial because it yields key insights into the moisture-induced damages of asphalt pavement. In this work, the molecular ...dynamics simulation technique was adopted to characterize the diffusion and structural properties of moisture (water molecules) in both neat asphalt binder and asphalt mastic. Microstructural changes during the diffusion process, including free volume and hydrogen bond formation, were observed to clarify the mechanism of diffusion behavior at the atomistic level. The concentration dependence of moisture diffusion coefficient was revealed. Water molecules were well dispersed in the model and mainly formed hydrogen bonds with asphalt molecules at low concentrations. However, large water clusters were formed with the predominant formation of water−water hydrogen bonds and acceleration of diffusion at high concentrations. In the asphalt mastic system, silica particles not only introduced more free volume to speed up the diffusion of moisture but also intensified the affinity between moisture and the asphalt mastic system. Moreover, the relationship between the moisture diffusion and structural properties suggested that the diffusion of moisture in asphaltic materials is controlled by both the free volume and the cohesion property among asphalt chains. This relationship could be exploited to obtain information regarding diffusion behavior in the asphaltic material system and select materials to achieve excellent antistripping properties for the asphalt mixture.
Uranium is important in the nuclear fuel cycle both as an energy source and as radioactive waste. It is of vital importance to recover uranium from nuclear waste solutions for further treatment and ...disposal. Herein we present the first chalcogenide example, (Me2NH2)1.33(Me3NH)0.67Sn3S7·1.25H2O (FJSM-SnS), in which organic amine cations can be used for selective UO2 2+ ion-exchange. The UO2 2+-exchange kinetics perfectly conforms to pseudo-second-order reaction, which is observed for the first time in a chalcogenide ion-exchanger. This reveals the chemical adsorption process and its ion-exchange mechanism. FJSM-SnS has excellent pH stability in both strongly acidic and basic environments (pH = 2.1–11), with a maximum uranium-exchange capacity of 338.43 mg/g. It can efficiently capture UO2 2+ ions in the presence of high concentrations of Na+, Ca2+, or HCO3 – (the highest distribution coefficient K d value reached 4.28 × 104 mL/g). The material is also very effective in removing of trace levels of U in the presence of excess Na+ (the relative amounts of U removed are close to 100%). The UO2 2+···S2– interactions are the basis for the high selectivity. Importantly, the uranyl ion in the exchanged products could be easily eluted with an environmentally friendly method, by treating the UO2 2+-laden materials with a concentrated KCl solution. These advantages coupled with the very high loading capacity, low cost, environmentally friendly nature, and facile synthesis make FJSM-SnS a new promising remediation material for removal of radioactive U from nuclear waste solutions.
The fuel-air mixing process plays an important role in the shock-induced combustion ramjet (shcramjet) engine. In the current study, the investigation of front fuel jet and rear air jet is provided ...in order to study the mixing effect induced by the air jet and reveal the mixing augmentation mechanism and formation of several recirculation zones. Some parameters are also provided to evaluate the flow field properties quantitatively, namely the mixing efficiency, the total pressure recovery coefficient, the fuel penetration depth and the mixing length. The obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation shear stress transport (SST) k-ω turbulence model show that the additional air jet is really beneficial for accelerating the mixing process and improving the mixing efficiency. The shear vortex and air injected are the key sources for the mixing enhancement mechanism of the dual injection strategy. The formations of recirculation zones midstream and downstream are provided as well. The midstream recirculation zone “R2” is related to both front fuel jet and rear air jet, and “R3” is related to the air jet only. The downstream recirculation zone1 is composed by flows from the fuel jet and the air jet, and the downstream recirculation zone2 is formed by hydrogen flows.
•Mixing augmentation mechanism induced by the combination between the front fuel and rear air jets was explored numerically.•The air jet is beneficial for accelerating the mixing process and improving the mixing efficiency.•The air injection provides large amount air to accelerate mixing.•The shear vortex induced by the injection and the inflow produces more merge action.
PDF
