Degradation von Li-reichen xLi2MnO3:(1-x)Li(Ni1/3Co1/3Mn1/3)O2 Nanokompositen als Aktivmaterial für Lithium-Ionen Batterien

Fünf verschiedene Li-reiche Nanokomposite vom Typ xLi2MnO3:(1-x)Li(Ni1/3Mn1/3Co1/3)O2 mit den Zusammensetzungen x = 0,3, x = 0,5 (drei verschiedene Proben) und x = 0,7 wurden elektrochemisch und strukturell charakterisiert. Die elektrochemische Charakterisierung fand über galvanostatische Messungen in Knopfzellen gegen Lithium bis zum 70. Zyklus statt. Die Strukturanalyse wurde an den verschiedenen Proben im pristinen (unzyklierten) und formierten (nach erstem Zyklus) Zustand durchgeführt und jeweils nach fünf und nach 70 Zyklen. Die Nanokompositstruktur wurde über transmissionselektronenmikroskopische Methoden (TEM) bestimmt und die Interpretation der Hochauflösungsmuster (HRTEM) über entsprechende Simulationen unterstützt. Zusätzlich wurden Synchrotron Pulverdiffraktogramme der verschiedenen Materialien aufgenommen, um auch statistisch belastbare Aussagen zur Struktur zu erlangen, und über Rietveld-Verfeinerung und DIFFaX Simulationen ausgewertet. Es wurden auch in-situ Synchrotron Pulverbeugungsexperimente des Formierzyklus an Materialien mit der Zusammensetzung x = 0,5 und x = 0,7 durchgeführt. Durch Korrelation der gemessenen spezifischen Kapazitäten im ersten Zyklus mit den Strukturdaten wurde der Einfluss der pristinen Nanokompositstruktur auf die elektrochemischen Eigenschaften, insbesondere auf redoxaktiven Sauerstoff, isoliert. Eine besonders feine Nanokopositstruktur mit möglichst kleinen und gleichverteilten Li2MnO3 Domänen im Nanokomposit führt zu der höchsten reversiblen Kapazität und somit der stärksten Teilnahme des Sauerstoffs am Redoxprozess. Über eine Korrelation der strukturellen Veränderungen bei zunehmender Zyklenzahl mit den Veränderungen in der elektrochemischen Charakteristik wurde die Entwicklung einer LiMnO2 Schichtstruktur und einer LiMn2O4 spinellartigen Phase im Nanokomposit nachgewiesen. Für das Material, welchem die höchste reversible Sauerstoff Redoxaktivität nachgewiesen werden konnte, wurde die schnellste Umwandlung in die LiMnO2- und Spinell-Komponente detektiert. Es wird ein Modell präsentiert, welches die Entwicklung von LiMnO2 und Spinell in Abhängigkeit von redoxaktivem Sauerstoff erklären kann

Influence of annealing temperature on the mechanical properties of carbon supersaturated TaW coatings

The combination of ceramic hardness with metallic toughness is a major challenge in the development of protective coatings. The relative new concept of high entropy alloys (HEAs) can be a promising pathway to achieve new high-performance materials While HEA thin films have been studied to some extent by experimental and computational materials science, there is only limited information available about the influence of carbon on HEA thin films, especially when prepared with physical vapor deposition techniques. We have recently studied the properties of CrNbTaTiW thin films and observed a combination of high hardness and crack resistance for Ta and W-rich compositions when small amounts of carbon (\u3c 10 at%) is added [1]. To increase our understanding of the properties of these multicomponent HEA films, we have studied the influence of temperature and carbon on the structure and properties alloys in the ternary TaW-C system. The Ta-W-C thin films were deposited by non-reactive magnetron sputtering from elemental targets. The material properties were strongly depending on the carbon content. The TaW films crystallise in a bcc structure with a strong (110) texture with coherent grain boundaries. TEM analysis revealed that the films exhibit coherent grain boundaries with specific crystallographic directions. The addition of 8 at.% led to the formation of a metastable bcc supersaturated solid-solution without the formation of carbide precipitates. The main effect of the carbon addition was agrain refinement reducing the column width, which resulted in an increase in hardness from 14 to 16 GPa while the reduced E-modulus was unaffected. The enhanced hardness will be discussed in terms of solid solution hardening and grain refinement strengthening. The films were also annealed up to 900 °C to investigate the thermal stability. The TaW(C) remained in the bcc structure and no carbide formation was observed. Furthermore, the annealing had an age-hardening effect leading to a peak hardness of 26 GPa. These results indicate that TaW-C alloys are suitable for future high temperature application. [1] S. Fritze, P. Malinovskis, L. Riekehr, L. von Fieandt, E. Lewin, U. Jansson, Hard and crack resistant carbon supersaturated refractory multicomponent nanostructured coatings, Sci. Rep. (2018) 1–8

Review over international forskningslitteratur om digitale læringsplatforme

DA: Denne artikel afsøger den seneste internationale engelsk­sprogede forskningslitteratur om anvendelse af digitale lærings­platforme. Reviewet behandler forskning fra i alt 21 studier og sammenfatter resultaterne i tre hovedkategorier, der henholds­vis omfatter implementering af læringsplatforme, kompetence­udviklingsbehov i forbindelse med platforme og relationen mellem elevers brug af platforme og deres faglige udbytte. Reviewet afsluttes med en diskussion af, hvordan resultaterne af litteraturgennemgangen kan have relevans for en dansk uddan­nelseskontekst i forhold til særlige opmærksomhedspunkter i den pædagogiske praksis, forskning og beslutningstagning.ENG: The article is a review of current international research literature on the use of digital learning platforms in educational settings. The review includes a total of 21 studies and summarizes the results in three main categories: 1. Support of students’ learning and performance, 2. implementation of digital learning platforms, and 3. competence development of instructors. The relevance of the results in a Danish educational context is discussed in relation to educational practice, research and decision making.The article is a review of current international research literature on the use of digital learning platforms in educational settings. The review includes a total of 21 studies and summarizes the results in three main categories: 1. Support of students’ learning and performance, 2. implementation of digital learning platforms, and 3. competence development of instructors. The relevance of the results in a Danish educational context is discussed in relation to educational practice, research and decision making

Perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage

Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 (x=0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization (Pr) and high maximum polarization (Pmax). Moreover, Pmax was further increased due to reversible electric field induced phase transitions. Comprehensive structural and electrical studies were performed to confirm the PNRs and the reversible phase transitions. And finally a high energy density (1.70 J/cm3) with an excellent efficiency (87.2%) was achieved using the contribution of PNRs and field-induced transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage

Degradation von Li-reichen xLi2MnO3:(1-x)Li(Ni1/3Co1/3Mn1/3)O2 Nanokompositen als Aktivmaterial für Lithium-Ionen Batterien

Fünf verschiedene Li-reiche Nanokomposite vom Typ xLi2MnO3:(1-x)Li(Ni1/3Mn1/3Co1/3)O2 mit den Zusammensetzungen x = 0,3, x = 0,5 (drei verschiedene Proben) und x = 0,7 wurden elektrochemisch und strukturell charakterisiert. Die elektrochemische Charakterisierung fand über galvanostatische Messungen in Knopfzellen gegen Lithium bis zum 70. Zyklus statt. Die Strukturanalyse wurde an den verschiedenen Proben im pristinen (unzyklierten) und formierten (nach erstem Zyklus) Zustand durchgeführt und jeweils nach fünf und nach 70 Zyklen. Die Nanokompositstruktur wurde über transmissionselektronenmikroskopische Methoden (TEM) bestimmt und die Interpretation der Hochauflösungsmuster (HRTEM) über entsprechende Simulationen unterstützt. Zusätzlich wurden Synchrotron Pulverdiffraktogramme der verschiedenen Materialien aufgenommen, um auch statistisch belastbare Aussagen zur Struktur zu erlangen, und über Rietveld-Verfeinerung und DIFFaX Simulationen ausgewertet. Es wurden auch in-situ Synchrotron Pulverbeugungsexperimente des Formierzyklus an Materialien mit der Zusammensetzung x = 0,5 und x = 0,7 durchgeführt. Durch Korrelation der gemessenen spezifischen Kapazitäten im ersten Zyklus mit den Strukturdaten wurde der Einfluss der pristinen Nanokompositstruktur auf die elektrochemischen Eigenschaften, insbesondere auf redoxaktiven Sauerstoff, isoliert. Eine besonders feine Nanokopositstruktur mit möglichst kleinen und gleichverteilten Li2MnO3 Domänen im Nanokomposit führt zu der höchsten reversiblen Kapazität und somit der stärksten Teilnahme des Sauerstoffs am Redoxprozess. Über eine Korrelation der strukturellen Veränderungen bei zunehmender Zyklenzahl mit den Veränderungen in der elektrochemischen Charakteristik wurde die Entwicklung einer LiMnO2 Schichtstruktur und einer LiMn2O4 spinellartigen Phase im Nanokomposit nachgewiesen. Für das Material, welchem die höchste reversible Sauerstoff Redoxaktivität nachgewiesen werden konnte, wurde die schnellste Umwandlung in die LiMnO2- und Spinell-Komponente detektiert. Es wird ein Modell präsentiert, welches die Entwicklung von LiMnO2 und Spinell in Abhängigkeit von redoxaktivem Sauerstoff erklären kann

Magnetron Sputtering of Nanolaminated Cr2AlB2

A ternary Cr(2)AlB(2)phase was deposited as a film using magnetron sputtering. Its anisotropic structure displays both structural and chemical similarities with the nanolaminated MAX phases (M(n+1)AX(n)(n = 1-3) where M usually is an early transition metal, A is typically an element in group 13-14 and X is C or N), and can be described as CrB slabs separated by layers of Al. Combinatorial sputtering was used to optimise the sputtering process parameters for films with the Cr(2)AlB(2)composition. The influences of substrate, temperature and composition were studied using X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. Films deposited at room temperature were X-ray amorphous but crystalline films could be deposited on MgO substrates at 680 degrees C using a composite Al-B, Cr and Al targets. X-ray diffraction analyses showed that the phase composition and texture of the films was strongly dependent on the chemical composition. Films with several phases or with a single Cr(2)AlB(2)phase could be deposited, but an additional Al target was required to compensate for a loss of Al at the high deposition temperatures used in this study. The microstructure evolution during film growth was strongly dependent on composition, with a change in texture in Al-rich films from a preferred [010] orientation to a [100]/[001] orientation. A model based on Al desorption from the surface of the growing grains is proposed to explain the texture variations

Phase formation in magnetron sputtered CrMnFeCoNi high entropy alloy

Thin films of the CrMnFeCoNi high entropy alloy were deposited by magnetron sputtering from a sintered equimolar target. The substrate temperature and bias were varied during deposition, and the structure, morphology and elemental distribution were studied in detail. All films formed phase mixtures of multiple crystal structures. This contrasts with studies on the bulk alloy, where it typically forms a single phase with a simple cubic closed packed (ccp) structure, with other phases precipitating only after long annealing times. For higher substrate temperatures, we observed a mixture of phases with ccp and bcc (body centered cubic) structures, and the intermetallic phases o-phase and L1(0), the first three being the predicted equilibrium phases at the deposition temperature. For room temperature depositions, we found evidence of very limited diffusion of metal atoms during the deposition. These films formed a mixture of a ccp and the intermetallic chi-phase. Two mechanisms can be distinguished that govern the phase formation at lower and higher temperatures. From the present results and comparisons with the literature, we also discuss why the small grain size, the low process temperature, and the fast surface diffusion during synthesis causes magnetron sputtering to yield different results compared to bulk synthesis from the melt. These principles explain why it is easier to form the equilibrium phases by sputtering, and why a single ccp phase should not be expected as a rule for this deposition method. Following the thermodynamic principles of high entropy alloys, this may also be the case in other high entropy alloy systems

On the Paramount Role of Absorber Stoichiometry in (Ag,Cu)(In,Ga)Se2 Wide‐Gap Solar Cells

This contribution evaluates the effect of absorber off‐stoichiometry in wide‐gap (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells. It is found that ACIGS films show an increased tendency to form ordered vacancy compounds (OVCs) with increasing Ga and Ag contents. Very little tolerance to off‐stoichiometry is detected for absorber compositions giving the desired properties of 1) an optimum bandgap (EG) for a top cell in tandem devices (EG = 1.6–1.7 eV) and at the same time 2) a favorable band alignment with a CdS buffer layer. Herein, massive formation of either In‐ or Ga‐enriched OVC patches is found for group I‐poor ACIGS. As a consequence, carrier transport and charge collection are significantly impeded in corresponding solar cells. The transport barrier appears to be increasing with storage time, questioning the long‐term stability of wide‐gap ACIGS solar cells. Furthermore, the efficiency of samples with very high Ga and Ag contents depends on the voltage sweep direction. It is proposed that the hysteresis behavior is caused by a redistribution of mobile Na ions in the 1:1:2 absorber lattice upon voltage bias. Finally, a broader perspective on OVC formation in the ACIGS system is provided and fundamental limitations for wide‐gap ACIGS solar cells are discussed.