The role of the alkali metal cations in halide perovskite solar cells is not well understood. Using synchrotron-based nano-x-ray fluorescence and complementary measurements, we found that the halide ...distribution becomes homogenized upon addition of cesium iodide, either alone or with rubidium iodide, for substoichiometric, stoichiometric, and overstoichiometric preparations, where the lead halide is varied with respect to organic halide precursors. Halide homogenization coincides with long-lived charge carrier decays, spatially homogeneous carrier dynamics (as visualized by ultrafast microscopy), and improved photovoltaic device performance. We found that rubidium and potassium phase-segregate in highly concentrated clusters. Alkali metals are beneficial at low concentrations, where they homogenize the halide distribution, but at higher concentrations, they form recombination-active second-phase clusters.
Mechanical integrity issues such as particle cracking are considered one of the leading causes of structural deterioration and limited long-term cycle stability for Ni-rich cathode materials of ...Li-ion batteries. Indeed, the detrimental effects generated from the crack formation are not yet entirely addressed. Here, applying physicochemical and electrochemical ex situ and in situ characterizations, the effect of Co and Mn on the mechanical properties of the Ni-rich material are thoroughly investigated. As a result, we successfully mitigate the particle cracking issue in Ni-rich cathodes via rational concentration gradient design without sacrificing the electrode capacity. Our result reveals that the Co-enriched surface design in Ni-rich particles benefits from its low stiffness, which can effectively suppress the formation of particle cracking. Meanwhile, the Mn-enriched core limits internal expansion and improve structural integrity. The concentration gradient design also promotes morphological stability and cycling performances in Li metal coin cell configuration.
A systematic study of the effects of up to 1.1 at. % carbon on the mechanical properties and evolution of the dislocation substructure in a series of a high entropy alloys (HEA) based on ...Fe40.4Ni11.3Mn34.8Al7.5Cr6 is presented. Transmission electron microscopy (TEM), synchrotron X-ray diffraction (XRD) and atom probe tomography (APT) were used to show that all the alloys are single-phase f.c.c. random solid solutions. The lattice constant, determined from synchrotron XRD measurements, increases linearly with increasing carbon concentration, which leads to a linear relationship between the yield strength and the carbon concentration. The dislocation substructures, as determined by a TEM, show a transition from wavy slip to planar slip and, at higher strains, and from cell-forming structure (dislocations cells, cell blocks and dense dislocation walls) to non-cell forming structure (Taylor lattice, microbands and domain boundaries) with the addition of carbon, features related to the increase in lattice friction stress. The stacking fault energy (measured via weak-beam imaging of the separation of dislocation partials) decreases with increasing carbon content, which also contributes to the transition from wavy slip to planar slip. The formation of non-cell forming structure induced by carbon leads to a high degree of strain hardening and a substantial increase in the ultimate tensile strength. The consequent postponement of necking due to the high strain hardening, along with the plasticity accommodation arising from the formation of microbands and domain boundaries, result in an increase of ductility due to the carbon addition.
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•Anomalous evolution of Fe based intermetallic phases in Al–Si–Fe alloys.•XRF coupled with nano-diffraction to confirm the nano-size Fe intermetallic phases.•Crystallography of the θ-Al13Fe4, ...τ5-Al8Fe2Si and τ6-Al9Fe2Si2 phases.•Peritectic reactions involving the Fe intermetallic phases in Al–Si–Fe alloys.
Al–Si–Fe hypoeutectic cast alloy system is very complex and reported to produce numerous Fe based intermetallic phases in conjunction with Al and Si. This publication will address the anomalies of phase evolution in the Al–Si–Fe hypoeutectic casting alloy system; the anomaly lies in the peculiarities in the evolution and nature of the intermetallic phases when compared to the thermodynamic phase diagram predictions and past publications of the same. The influence of the following parameters, in various combinations, on the evolution and nature of the intermetallic phases were analyzed and reported: concentration of Si between 2 and 12.6wt%, Fe between 0.05 and 0.5wt% and solidification rates of 0.1, 1, 5 and 50Ks−1. Two intermetallic phases are observed to evolve in these alloys under these solidification conditions: the τ5-Al8SiFe2 and τ6-Al9Fe2Si2. The τ5-Al8SiFe2 phase evolves at all levels of the parameters during solidification and subsequently transforms into the τ6-Al9Fe2Si2 through a peritectic reaction when promoted by certain combinations of solidification parameters such as higher Fe level, lower Si level and slower solidification rates. Further, it is also hypothesized from experimental evidences that the θ-Al13Fe4 binary phase precludes the evolution of the τ5 during solidification and subsequently transforms into the τ6 phase during solidification. These observations are anomalous to the publications as prior art and simulation predictions of thermodynamic phase diagrams of these alloys, wherein, only one intermetallic phases in the τ6-Al9Fe2Si2 is predicted to evolve and be retained as the terminal phase at the end of solidification. Several analysis methods such as light optical microscope, scanning electron microscope equipped with a dual beam focused ion beam milling machine and energy dispersive X-ray diffraction system, transmission electron microscope equipped with high resolution digital imaging system, energy dispersive X-ray diffraction system, and high energy synchrotron beam source for nano-diffraction coupled with X-ray fluorescence imaging system was used in this study.
Developing a precise and reproducible bandgap tuning method that enables tailored design of materials is of crucial importance for optoelectronic devices. Towards this end, we report a sphere ...diameter engineering (SDE) technique to manipulate the bandgap of two-dimensional (2D) materials. A one-to-one correspondence with an ideal linear working curve is established between the bandgap of MoS
and the sphere diameter in a continuous range as large as 360 meV. Fully uniform bandgap tuning of all the as-grown MoS
crystals is realized due to the isotropic characteristic of the sphere. More intriguingly, both a decrease and an increase of the bandgap can be achieved by constructing a positive or negative curvature. By fusing individual spheres in the melted state, post-synthesis bandgap adjustment of the supported 2D materials can be realized. This SDE technique, showing good precision, uniformity and reproducibility with high efficiency, may further accelerate the potential applications of 2D materials.
Diamond anvil cell behavior up to 4 Mbar Li, Bing; Ji, Cheng; Yang, Wenge ...
Proceedings of the National Academy of Sciences - PNAS,
02/2018, Letnik:
115, Številka:
8
Journal Article
Recenzirano
Odprti dostop
The diamond anvil cell (DAC) is considered one of the dominant devices to generate ultrahigh static pressure. The development of the DAC technique has enabled researchers to explore rich ...high-pressure science in the multimegabar pressure range. Here, we investigated the behavior of the DAC up to 400 GPa, which is the accepted pressure limit of a conventional DAC. By using a submicrometer synchrotron X-ray beam, double cuppings of the beveled diamond anvils were observed experimentally. Details of pressure loading, distribution, gasket-thickness variation, and diamond anvil deformation were studied to understand the generation of ultrahigh pressures, which may improve the conventional DAC techniques.
One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide ...perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX3 (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensurate epitaxy, paving a way for a universally applicable method to grow a broad family of halide perovskite materials. The unique photon transport in the one-dimensional structure has been studied in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.
The microstructure and mechanical properties studies of a series of two-phase f.c.c./B2 (ordered b.c.c.) lamellar-structured, high entropy alloys (HEA) Fe36Ni18Mn33Al13Tix with x up to 6 at. % Ti ...have been investigated. X-ray microanalysis in a TEM showed that the Ti resided mostly in the B2 phase. The lamellar spacing decreased significantly with increasing Ti content from 1.56 μm for the undoped alloy to 155 nm with an addition of 4 at. % Ti, leading to a sharp increase in room-temperature yield strength,σy, from 270 MPa to 953 MPa, but with a concomitant decrease in ductility from 22% elongation to 2.3%. Annealing at 1173 K for 20 h greatly increased the lamellar spacing of Fe36Ni18Mn33Al13Ti4 to 577 nm, producing a corresponding decrease in σy to 511 MPa. The yield strengths of all the doped alloys decreased significantly when tensile tested at 973 K with a concomitant increase in ductility due to softening of the B2 phase. The fracture mode changed from cleavage at room temperature to a ductile dimple-type rupture at 973 K. The results are discussed in terms of the Hall-Petch-type relationship.
•The lamellar spacing decreased significantly with increasing Ti content.•Ti resided mostly in the B2 phase.•Ti led to a sharp increase in room-temperature yield strength (up to 953 MPa).•The strengthening effect of Ti on the yield strength can be described by a Hall-Petch-type relationship.
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