Luminescence-site symmetry correlations in Dy3+ doped alkali-alkaline earth orthoborates of the type XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba. - In: Journal of luminescence. - New York, NY [u.a.] : Elsevier, ISSN 0022-2313, Bd. 241 (2022)
- Im Titel ist "3+" hochgestellt und "3" tiefgestellt
A systematic investigation of the luminescence properties of Dy3+ doped alkali-alkaline earth orthoborates of the stoichiometric composition XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba was conducted. XRD diffractograms show that the compounds LiMgBO3, LiCaBO3, LiBaBO3, NaMgBO3, NaCaBO3, NaBaBO3, and KMgBO3 could be produced in high purity. Relatively intense luminescence was observed only for the phases LiCaBO3, NaMgBO3, NaCaBO3 and NaBaBO3. Micro Raman investigations show that the Dy3+ luminesence mainly originates from the orthoborate phase in these samples. Photo-luminescence spectroscopy of LiCaBO3, NaCaBO3 and NaBaBO3 shows the typical Dy3+ emission with the prominent emission peak in the yellow spectral range around 575 nm. A second, but much less intense peak is observed at around 485 nm (cyan). The luminescence emission spectrum of Dy3+:NaMgBO3 is much different: here, the highest emission intensity is observed at about 485 nm. It is proposed that the Dy3+ ions occupy the Na positions in this crystal phase which has a much higher symmetry than the alkaline earth positions in the other examined crystal phases. This is supported by broadened and more split up peaks in the excitation and emission spectra of Dy3+:NaMgBO3 suggesting a much stronger local crystal field at the rare earth position in this compound. The results are additionally compared to spectroscopic data of different well known Dy3+ doped crystalline compounds and Dy3+ and Eu3+ doped alkali-alkaline earth orthoborates from other publications, which offer further insight into the relation between the crystallographic sites of the doped rare earth ions and their luminescence.
Construction of Co0.85Se@nickel nanopores array hybrid electrode for high-performance asymmetric supercapacitors. - In: Chemical engineering science. - Amsterdam [u.a.] : Elsevier Science, Bd. 247 (2022), S. 1-9
Nanostructured current collectors have larger specific surface area and short ion/electron transport path, which are highly desirable for supercapacitors applications. Herein, Co0.85SeNiNPs (Co0.85Se@NiNP) hybrid electrodes are proposed and fabricated, in which NiNP is served as nanostructured current collectors. NiNP has a vertical pore structure and a large specific surface area, which could effectively promote the ion/electron transport efficiency and reduce internal electrical resistance. Compared with Ni foam and Ni foil as current collectors, NiNP enables Co0.85Se@NiNP electrodes show significantly improved specific capacity, rate performance and cycle stability. Finally, an asymmetric supercapacitor device was assembled with Co0.85Se@NiNP hybrid electrode as the binder-free positive electrode and activated carbon (AC) coated on nickel foam as negative electrode. The Co0.85Se@NiNP//AC asymmetric supercapacitors can work in a wide potential window of 0 - 1.6 V with an ultrahigh specific capacity of 182.3 F g^-1 at 1 A g^-1. Most importantly, Co0.85Se@NiNP//AC has a high energy density of 64.81 Wh kg^-1 at 800 W kg^-1 and an outstanding cycle stability of up to 12000 cycles, indicating that Co0.85Se@NiNP electrode has great application potential in supercapacitors.
Corrosion of aluminium current collector in lithium-ion batteries: a review. - In: Journal of energy storage. - Amsterdam [u.a.] : Elsevier, ISSN 2352-152X, Bd. 43 (2021)
Calendar and cycle ageing affects the performance of the lithium-ion batteries from the moment they are manufactured. An important process that occurs as a part of the ageing is corrosion of the current collectors, especially prominent in the case of the aluminium substrate for the positive electrode. Generally, aluminium resists corrosion due to the formation of a non-permeable film of native aluminium oxide. Nevertheless, at certain electrochemical conditions corrosion affects the interface of the current collector. As a consequence of corrosion, the cathode materials lose electrical and mechanical contact with the current collector, leading to capacity and power fading. Therefore, a deeper understanding of this process and effective corrosion inhibition are necessary to prevent the deterioration of the battery performance. This review provides an updated critical overview of the mechanisms of aluminium corrosion, methodologies for analysing this phenomenon, and approaches for its effective mitigation. As the influence of multiple factors on the corrosion process has a central impact, the review discusses how they specifically affect the undergoing processes. Therefore, appropriate examples of important factors like electrolyte composition, thermal conditions and electrochemical parameters are presented to explain the specific mechanism of aluminium corrosion. Since corrosion inhibition is an important technological issue with a tremendous economic impact the review summarises how to achieve this by adjusting the electrochemical system and enhancing the knowledge on the safe operation of the positive electrode.
Efficient preparation of Ni-M (M = Fe, Co, Mo) bimetallic oxides layer on Ni nanorod arrays for electrocatalytic oxygen evolution. - In: Applied materials today. - Amsterdam [u.a.] : Elsevier, ISSN 2352-9407, Bd. 25 (2021)
Fabrication of economic and high-performance electrodes for electrocatalytic oxygen evolution reaction (OER) accounts for a crucial issue associated with developing powerful and practical water splitting systems. In this work, free-standing Ni/Ni-M (M = Fe, Co, Mo) bimetallic oxides core/shell nanorod arrays (Ni/Ni-M NRAs) were prepared through electroless deposition of transition metal species on black nickel sheet (nickel nanorod arrays (Ni NRAs)) followed by electrochemical oxidation. All three types of Ni/Ni-M NRAs demonstrated enhanced electrocatalytic activity toward oxygen evolution reactions (OER). Especially, Ni/Ni-Fe NRAs electrode exhibit small onset potential of 1.535 V at current density of 10 mA&hahog;cm^-2. In contrast, the OER durability of these three samples was distinct. At 500 mV constant overpotential, the current density loss in OER of Ni/Ni-Fe NRAs was merely 13.5% for a period of 20000 s; but Ni/Ni-Mo and Ni/Ni-Co NRAs had almost disappeared catalytic activity under the identical conditions. According to many reports, the results were different for the superior OER stability of Ni-based bimetallic catalysts. Electrochemical analysis revealed that the NRAs structure dramatically improves charge transfer efficiency and electrochemically active surface area (ECSA). The present study might provide a new insight to design and fabricate more practical and high-performance Ni-based electrodes for OER.
Rapid fabrication and interface structure of highly faceted epitaxial Ni-Au solid solution nanoparticles on sapphire. - In: Acta materialia. - Amsterdam [u.a.] : Elsevier Science, ISSN 1359-6454, Bd. 220 (2021), S. 1-12
Supersaturated Ni-Au solid solution particles were synthesized by rapid solid-state dewetting of bilayer thin films deposited onto c-plane sapphire single-crystals. Rapid thermal annealing above the miscibility gap of the Ni-Au system followed by quenching to room temperature resulted in textured and faceted submicron-sized particles as a function of alloying content in the range of 0-28 at% Au. Morphologically, the observed kinetic crystal shapes are confined by close-packed planes; in addition, high-index facets are identified as a function of alloying content by TEM cross-sectioning and equilibrium crystal shape simulations. All samples exhibit a distinct <111> out-of-plane as well as in-plane texture along densely packed directions. Lattice parameters extracted from independent orthogonal X-ray and electron diffraction techniques prove the formation of a solid solution without tetragonal distortion imposed by the sapphire substrate. At the particle-substrate interface of highly alloyed particles segregation of Au atoms as well as dislocations in stand-off position are found. These observations are in-line with a semi-coherent interface, where Au segregation is triggered by the reduction of the overall strain energy due to: (i) a lower shear modulus on the particle side of the interface, (ii) the shifting of misfit dislocations in stand-off position further away from the stiffer substrate and (iii) a reduction of intrinsic misfit dislocation strain energy on the tensile side. In addition, the mechanical properties of pure and alloyed particles were characterized by in situ compression experiments in the SEM. Typical force-displacement data of defect-free single-crystals were obtained, reaching the theoretical strength of Ni for particles smaller than 400 nm. Alloying changes the mechanical response from an intermittent and discrete plastic flow behavior into a homogeneous deformation regime at large compressive strain.
Specific electrical contact resistance of copper in resistance welding. - In: Physica status solidi. - Weinheim : Wiley-VCH, ISSN 1521-396X, Bd. 218 (2021), 19, S. 1-11
The electrical contact resistance (ECR) of copper (Cu-ETP R200, soft) contacts for resistance welding (RW) is characterized. ECR plays a major role in the RW process and provides local heat generation between the parts. A special determination method is used on different testing variants to observe the influence of contact pressure (two levels: 68, 155 MPa), contact temperature (20-550 ˚C), and surface parameters, like roughness or oxide layer thickness, on the specific electrical contact resistance (SECR). For each surface parameter, three different levels are investigated. The study shows decreasing SECR with higher mechanical load on the contact and a more complex behavior for increase in contact temperature. SECR shows a characteristic behavior for contact states near the temperature-dependent tensile strength of the base material for rough and clean surfaces, where SECR approaches toward zero. The variation of oxide layer thickness and surface roughness has a strong influence on the resulting SECR and both surface parameters show a strong coupling regarding their effects.
Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion. - In: Nanotechnology. - Bristol : IOP Publ., ISSN 1361-6528, Bd. 32 (2021), 50, S. 1-27
Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.
Yttrium and rare-earth modified lithium orthoborates: glass formation and vibrational activity. - In: Journal of non-crystalline solids : a journal on the chemical, electronic, optical and mechanical properties of glasses, amorphous semiconductors and metals, sol-gel materials, the liquid state of these solids and the processes by which they are formed.. - Amsterdam [u.a.] : Elsevier Science, ISSN 0022-3093, (2021)
Glass formation and structure-property relations were explored in highly modified borate glasses containing high loads of rare-earth elements, whose crystalline analogues display a trigonal to tetrahedral borate phase transition (BO33- -> BØ2O23-, where Ø and O- indicate bridging and non-bridging oxygen atoms). The resulting borate networks are completely depolymerized, where borate anions are crosslinked to rare-earth and modifier cations via ionic bonds. The borate structure was found to be based on a single structural unit, BO33- triangles, whose fundamental vibrations are all active in both the Raman and infrared. The local environment of the rare-earth ions in orthoborate glasses was studied with far infrared spectroscopy and, in some cases, by using terbium as a probe ion. A linear correlation was obtained between the effective force constant in the far infrared and the field strength of the rare-earth cation.
Probing transient localized electromagnetic fields using low-energy point-projection electron microscopy. - In: ACS photonics. - Washington, DC : ACS, ISSN 2330-4022, Bd. 8 (2021), 9, S. 2573-2580
Low kinetic energy electrons are of interest for probing nanoscale dynamic processes using ultrafast electron microscopy techniques. Their low velocities reduce radiation doses and enhance the interaction with confined electromagnetic fields and, thus, may enable ultrafast spectroscopy of single nanostructures. Recent improvements in the spatial and temporal resolution of ultrafast, low-energy electron microscopy have been achieved by combining nanotip photoemitters and point-projection imaging schemes. Here, we use such an ultrafast point-projection electron microscope (UPEM) to analyze the interaction of low-energy electrons with transient electric fields created by photoemission from a nanogap antenna. By analyzing their kinetic energy distribution, we separate angular deflection due to radial field components from electron energy gain and loss due to their axial acceleration. Our measurements open up a route toward the spatial and temporal characterization of vectorial near-fields by low-energy electron streaking spectroscopy.
Cost-effective sensor for flow monitoring in biologic microreactors. - In: IEEE sensors journal. - New York, NY : IEEE, ISSN 1558-1748, Bd. 21 (2021), 19, S. 21314-21321