Project description:The new compound Ba4Al7Li28.08O26.92N1.08 consists of AlO4/AlO3N tetrahedra, 10-fold coordinated Ba2+ cations, and a highly condensed edge- and corner-sharing LiO4 tetrahedra framework, which leads to a degree of condensation greater than 1. The first barium oxonitridolithoaluminate was synthesized by a high-temperature solid-state reaction in a weld-shut tantalum ampoule and the crystal structure has been determined by single-crystal X-ray diffraction. Ba4Al7Li28.08O26.92N1.08 crystallizes in the monoclinic space group P21/m (no. 11) with the lattice parameters a = 1052.41(3), b = 615.93(2), c = 1088.45(4) pm, β = 98.86(1)°, and a volume of V = 0.69712(4) nm3. In addition, Ba4Al7Li28.08O26.92N1.08 doped with the activator ion Eu2+, exhibits a broad band emission with a maximum at λmax = 524 nm (2.34 eV) with a fwhm of 112 nm (4373 cm-1/0.54 eV), which can be described by a superposition of two adjusted emission bands at λmax = 515 nm (2.41 eV) with a fwhm of 70 nm (2704 cm-1/0.34 eV), and at λmax = 574 nm (2.18 eV) with a fwhm of 127 nm (4127 cm-1/0.51 eV).
Project description:The adjustable conductance of a two-terminal memristor in a crossbar array can facilitate vector-matrix multiplication in one step, making the memristor a promising synapse for efficiently implementing neuromorphic computing. To achieve controllable and gradual switching of multi-level conductance, important for neuromorphic computing, a theoretical design of a superlattice-like (SLL) structure switching layer for the multi-level memristor is proposed and validated, refining the growth of conductive filaments (CFs) and preventing CFs from the abrupt formation and rupture. Ti/(HfOx /AlOy )SLL /TiN memristors are shown with transmission electron microscopy , X-ray photoelectron spectroscopy , and ab initio calculation findings corroborate the SLL structure of HfOx /AlOy film. The optimized SLL memristor achieves outstanding conductance modulation performance with linearly synaptic weight update (nonlinear factor α = 1.06), and the convolutional neural network based on the SLL memristive synapse improves the handwritten digit recognition accuracy to 94.95%. Meanwhile, this improved synaptic device has a fast operating speed (30 ns), a long data retention time (≥ 104 s at 85 ℃), scalability, and CMOS process compatibility. Finally, its physical nature is explored and the CF evolution process is characterized using nudged elastic band calculations and the conduction mechanism fitting. In this work, as an example the HfOx /AlOy SLL memristor provides a design viewpoint and optimization strategy for neuromorphic computing.
Project description:Up to now, the thermal expansion behavior of multiphase glass-ceramics cannot be predicted reliably because of the nescience about the formation of the type and concentration of crystalline phases. In the system BaO-SrO-ZnO-SiO2, recently a new phase based on Ba1-xSrxZn2Si2O7 solid solutions was found, which exhibits unexpected low and highly anisotropic thermal expansion, which can be used for an adjustment of the thermal expansion properties. In the case of sealing materials for high-temperature reactors, the formation of this phase should be avoided. Hence, in this manuscript the concentration thresholds in which these solid solutions precipitate from glasses were determined. The phase analysis was correlated with the thermal expansion behavior of the glass-ceramics. Depending on the Ba/Sr-ratio of the glasses and the considered temperature range, the coefficients of thermal expansion of the glass-ceramics vary between 19.4·10-6?K-1 and 4.8·10-6?K-1. The concentration thresholds in which the as mentioned phases form via crystallization of glasses differ strongly from the literature values obtained via conventional ceramic mixed oxide route.
Project description:The dye industry is one of the largest water consuming industries, and at the same time generates large quantities of wastewaters. The resulting wastewaters require proper treatment before discharge, because the dye contents have a negative effect on the water body and organisms present in it. The most efficient treatment method for water containing dyes is represented by adsorption processes. The challenge with these adsorption processes is to develop new, efficient, viable, and economic adsorbent materials. Therefore, in the present paper, the performance of Zn2Al-layered double hydroxide, prepared from an industrial waste (zinc ash) as a zinc source, was investigated in the Orange II dye adsorption process. The Zn2Al-layered double hydroxide prepared from secondary sources presents similar morphological and structural characteristics as those prepared from analytical grade reagents. The influence of initial dye concentration, adsorption time, solid:liquid ratio, pH, and temperature was evaluated in order to confirm the benefit of this waste valorization. A comparison with the reference Zn2Al-layered double hydroxide prepared from analytical grade reagents was performed and the results show that due to the small presence of impurities, the material prepared from zinc ash shows better adsorption capacities (qmax,exp = 42.5 mg/g at 293 K) than the material prepared from reagents (qmax,exp = 36.9 mg/g at 293 K), justifying the utilization of secondary sources for layered double hydroxides preparation. The proposed treatment process presents advantages from both economic and environmental protection point of view.
Project description:Corrosion is a harmful processes which by definition is a chemical or electrochemical reaction between a substance (usually a metal) and the environment which leads to a change in the properties of the substance and has destructive effects. In this study, new composites consisting of Al/WS2/ZnTerp-2TH with 5 and 10 wt.% ZnTerp-2TH were prepared and the results were fully compared. Al/WS2 played the role of matrix and ZnTerp-2TH played the role of reinforcement. In other words, as a novelty to prevent the corrosion of Al/WS2, ZnTerp-2TH is designed and synthesized and showed good results when the corrosion ratio was reduced by the existence of ZnTerp-2TH. Furthermore, the NMR and mass analysis of ZnTerp-2TH were carried out, and the thermal properties, X-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, morphology, energy-dispersive X-ray spectroscopy (EDX) analysis and corrosion behavior of the composites were also discussed in detail. The crystal size values of composites were calculated by the modified Scherrer method 34, 26 and 27 nm for Al/WS2, Al/WS2/5 wt.% ZnTerp-2TH and Al/WS2/10 wt.% ZnTerp-2TH, respectively. The microstructural examination of the specimens showed that the reinforcing phase (ZnTerp-2TH) has a favorable distribution on the surface of Al/WS2 when it covers the cracks and holes. In addition, the corrosion investigation results showed that the addition of ZnTerp-2TH to Al/WS2 can improve the corrosion resistance when the Ecorr and Icorr values of Al/WS2/10 wt.% ZnTerp-2TH were recorded in tandem -724 mV/decade and 5 uA cm-2.
Project description:Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate Ba8AlxGa16-xGe30 by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6c site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates Ba8AlxGa16-xGe30 and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties.
Project description:Metal-organic frameworks (MOFs) are promising gas adsorbents. Knowledge of the behavior of gas molecules adsorbed inside MOFs is crucial for advancing MOFs as gas capture materials. However, their behavior is not always well understood. In this work, carbon dioxide (CO2) adsorption in the microporous α-Zn3(HCOO)6 MOF was investigated. The behavior of the CO2 molecules inside the MOF was comprehensively studied by a combination of single-crystal X-ray diffraction (SCXRD) and multinuclear solid-state magnetic resonance spectroscopy. The locations of CO2 molecules adsorbed inside the channels of the framework were accurately determined using SCXRD, and the framework hydrogens from the formate linkers were found to act as adsorption sites. 67Zn solid-state NMR (SSNMR) results suggest that CO2 adsorption does not significantly affect the metal center environment. Variable-temperature 13C SSNMR experiments were performed to quantitatively examine guest dynamics. The results indicate that CO2 molecules adsorbed inside the MOF channel undergo two types of anisotropic motions: a localized rotation (or wobbling) upon the adsorption site and a twofold hopping between adjacent sites located along the MOF channel. Interestingly, 13C SSNMR spectroscopy targeting adsorbed CO2 reveals negative thermal expansion (NTE) of the framework as the temperature rose past ca. 293 K. A comparative study shows that carbon monoxide (CO) adsorption does not induce framework shrinkage at high temperatures, suggesting that the NTE effect is guest-specific.
Project description:In this study, the electric storage effect of AlO6 clusters in amorphous alumina (AAO) supercapacitors was investigated in terms of cluster morphologies under electron-beam irradiation. Based on first-principles density functional calculation, the optimised structure of AlO6 clusters around an O-vacancy is characterised by a large vacant space created by the absence of an O atom and its neighbouring Al atom. The localised electrons present near the two-atomic vacancies induce positive charges on the inside of the insulating oxide surface, ensuring the adsorption of many electrons on the surface. Electron-beam irradiation (adsorption) from 100 to 180 keV causes the lengths of the Al-O bonds of the cluster to shrink, but then return to the original length with decreasing voltage energy, indicating a rocking-chair-type charge-breathing effect accompanied by a volume expansion of approximately 4%. The I-V and I-R characteristics depicted Coulomb blockade for the switching effect of both the negative and positive potentials. The Ragone plot of the AAO supercapacitor is located at capability area of the second cell.
Project description:Metal-organic frameworks are promising materials for energy-efficient gas separations, but little is known about the diffusion of adsorbates in materials featuring one-dimensional porosity at the nanoscale. An understanding of the interplay between framework structure and gas diffusion is crucial for the practical application of these materials as adsorbents or in mixed-matrix membranes, since the rate of gas diffusion within the adsorbent pores impacts the required size (and therefore cost) of the adsorbent column or membrane. Here, we investigate the diffusion of CO2 within the pores of Zn2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations. The residual chemical shift anisotropy for pore-confined CO2 allows PFG NMR measurements of self-diffusion in different crystallographic directions, and our analysis of the entire NMR line shape as a function of the applied field gradient provides a precise determination of the self-diffusion coefficients. In addition to observing CO2 diffusion through the channels parallel to the crystallographic c axis (self-diffusion coefficient D∥ = (5.8 ± 0.1) × 10-9 m2 s-1 at a pressure of 625 mbar CO2), we unexpectedly find that CO2 is also able to diffuse between the hexagonal channels in the crystallographic ab plane (D⊥ = (1.9 ± 0.2) × 10-10 m2 s-1), despite the walls of these channels appearing impermeable by single-crystal X-ray crystallography and flexible lattice MD simulations. Observation of such unexpected diffusion in the ab plane suggests the presence of defects that enable effective multidimensional CO2 transport in a metal-organic framework with nominally one-dimensional porosity.
Project description:Cu/Ba/bauxite possesses superior NOx storage and reduction (NSR) performances, high thermal stability, strong resistance against SO? poisoning and outstanding regeneration ability in comparison with Pt/Ba/Al?O?. It can serve as a cheap and promising alternative for traditional Pt/Ba/Al?O? in NOx removal from lean-burn engines.