35 research outputs found
In operando Synchrotron XRD/XAS Investigation of Sodium Insertion into the Prussian Blue Analogue Cathode Material Na 1.32 Mn[Fe(CN) 6 ] 0.83 · z H 2 O
Prussian Blue Analogues (PBAs) with general formula NaxMA[MB(CN)6]y·z H2O (MA, MB = transition metal) are promising low cost, high rate and high capacity cathodes for sodium ion battery (SIB) technology. Here, we have studied the PBA Na1.32Mn[Fe(CN)6]0.83·z H2O (z = 3.0 and 2.2) with varying structural modifications (monoclinic and cubic) using in operando quasi-simultaneous X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). We observed a series of reversible structural phase transitions which accompany Na insertion/extraction during electrochemical cycling. The samples show pronounced differences in their galvanostatic charge and discharge profiles which could be linked to structural and electronic response. Different desodiation and sodiation mechanisms were identified. The influence of [Fe(CN)6] vacancies and water content on the electrochemical performance was investigated
High-pressure high-temperature stability of hcp-IrxOs1âx (x = 0.50 and 0.55) alloys
An in situ powder X-ray diffraction has been used for a monitoring a formation of hcp-Ir0.55Os0.45 alloy from (NH4)2[Ir0.55Os0.45Cl6] precursor. A crystalline intermediate compound and nanodimentional metallic particles with a large concentration of defects has been found as key intermediates in the thermal decomposition process in hydrogen flow. High-temperature stability of titled hcp-structured alloys has been investigated upon compression up to 11 GPa using a multi-anvil press and up to 80 GPa using laser-heated diamond-anvil cells to obtain a phase separation into fcc + hcp mixture. Obtained high-pressure high-temperature data allowed us to construct the first model for pressure-dependent IrâOs phase diagram
High-pressure high-temperature tailoring of High Entropy Alloys for extreme environments
The exceptional performance of some High Entropy Alloys (HEAs) under extreme conditions holds out the possibility of new and exciting materials for engineers to exploit in future applications. In this work, instead of focusing solely on the effects of high temperature on HEAs, the effects of combined high temperature and high pressure were observed. Phase transformations occurring in a pristine HEA, the as-cast bccâAl2CoCrFeNi, are heavily influenced by temperature, pressure, and by scandium additions. As-cast bccâAl2CoCrFeNi and fccâAl0.3CoCrFeNi HEAs are structurally stable below 60 GPa and do not undergo phase transitions. Addition of scandium to bccâAl2CoCrFeNi results in the precipitation of hexagonal AlScM intermetallic (W-phase), which dissolves in the matrix after high-pressure high-temperature treatment. Addition of scandium and high-pressure sintering improve hardness and thermal stability of well-investigated fcc- and bcc- HEAs. The dissolution of the intermetallic in the main phase at high pressure suggests a new strategy in the design and optimization of HEAs
Local Structure of EuropiumâDoped Luminescent Strontium Fluoride Nanoparticles: Comparative Xâray Absorption Spectroscopy and Diffraction Study
Rareâearth based luminescent materials are key functional components for the rational design of lightâconversion smart devices. Stable Eu3+âdoped strontium fluoride (SrF2) nanoparticles were prepared at room temperature in ethylene glycol. Their luminescence depends on the Eu content and changes after heat treatment. The crystallinity of heatâtreated material increases in comparison with asâsynthesized samples. Particles were investigated in solution using Xâray diffraction, smallâangle Xâray scattering, and Xâray spectroscopy. After heat treatment, the size of the disordered nanoparticles increases together with a change of their local structure. Interstitial fluoride ions can be localized near Eu3+ ions. Therefore, nonâradiative relaxation from other mechanisms is decreased. Knowledge about the cation distribution is key information for understanding the luminescence properties of any material.BAM funding program âIdeasâ (Menschen Ideen): New insights on the thermal behavior of luminescent nanoparticles from Sol-Gel synthesis by inâ
situ characterization â towards efficient upconversionPeer Reviewe
Formation and Disruption of W-Phase in High-Entropy Alloys
High-entropy alloys (HEAs) are single-phase systems prepared from equimolar or near-equimolar concentrations of at least five principal elements. The combination of high mixing entropy, severe lattice distortion, sluggish diffusion and cocktail effect favours the formation of simple phasesâusually a bcc or fcc matrix with minor inclusions of ordered binary intermetallics. HEAs have been proposed for applications in which high temperature stability (including mechanical and chemical stability under high temperature and high mechanical impact) is required. On the other hand, the major challenge to overcome for HEAs to become commercially attractive is the achievement of lightweight alloys of extreme hardness and low brittleness. The multicomponent AlCrCuScTi alloy was prepared and characterized using powder X-ray diffraction (PXRD), scanning-electron microscope (SEM) and atomic-force microscope equipped with scanning Kelvin probe (AFM/SKP) techniques. Results show that the formation of complex multicomponent ternary intermetallic compounds upon heating plays a key role in phase evolution. The formation and degradation of W-phase, Al2Cu3Sc, in the AlCrCuScTi alloy plays a crucial role in its properties and stability. Analysis of as-melted and annealed alloy suggests that the W-phase is favoured kinetically, but thermodynamically unstable. The disruption of the W-phase in the alloy matrix has a positive effect on hardness (890 HV), density (4.83 g·cmâ3) and crack propagation. The hardness/density ratio obtained for this alloy shows a record value in comparison with ordinary heavy refractory HEAs
Structure and magnetic property of potassium intercalated pentacene: observation of superconducting phase in KxC22H14
We report the results from systematic investigations on the structure and magnetic properties of potassium intercalated pentacene as a function of potassium content, K x C22H14 (1âââ€ââxâââ€ââ3). Synchrotron radiation powder x-ray diffraction technique revealed that there are two different stable phases can be obtained via potassium intercalation, namely, K1C22H14 phase and K3C22H14 phase. Structural phase transition was induced when the potassium content was increased to the nominal value xââ=ââ3. This phase transition is accompanied by drastic change in their magnetic property, where those samples with compositions K1C22H14 shows ferromagnetic behavior and those with near K3C22H14 lead to observation of superconductivity with transition temperature, T c, of 4.5âK. It is first time that superconductivity was observed in linear oligoacenes. Both magnetization study and synchrotron radiation powder x-ray diffraction clearly indicates that the superconducting phase belong to K3C22H14 as a result of phase transition from triclinic to monoclinic structure induced by chemical doping
Monoâ, Diâ, and TriâValent Cation Doped BiFe0.95Mn0.05O3 Nanoparticles: Ferroelectric Photocatalysts
The ferroelectricity of multivalent codoped Bismuth ferrite (BiFeO3; BFO) nanoparticles (NPs) is revealed and utilized for photocatalysis, exploiting their narrow electronic bandgap. The photocatalytic activity of ferroelectric photocatalysts BiFe0.95Mn0.05O3 (BFM) NPs and monoâ, diâ, or triâvalent cations (Ag+, Ca2+, Dy3+; MDT) coincorporated BFM NPs are studied under ultrasonication and in acidic conditions. It is found that such doping enhances the photocatalytic activity of the ferroelectric NPs approximately three times. The correlation of the photocatalytic activity with structural, optical, and electrical properties of the doped NPs is established. The increase of spontaneous polarization by the monoâ and triâvalent doping is one of the major factors in enhancing the photocatalytic performance along with other factors such as stronger light absorption in the visible range, low recombination rate of charge carriers, and larger surface area of NPs. Aâsite doping of BFO NPs by divalent elements suppresses the polarization, whereas trivalent (Dy3+) and monovalent (Ag+) cations provide an increase of polarization. The depolarization field in these single domain NPs acts as a driving force to mitigate recombination of the photoinduced charge carriers.The ferroelectricity of Ag/Ca/Dyâdoped BiFe0.95Mn0.05O3 nanoparticles are utilized for photocatalysis under ultrasonic conditions. The mitigated recombination of photoinduced chargeâcarriers in the nanoparticles due to the depolarization field, is one of the important factors for the photocatalytic rate. The piezoresponse becomes a crucial parameter under ultrasonic conditions for ferroelectric photocatalysts. The pink dye (rhodamine B) is photodegraded using MDT doped nanoparticles. The ease of photoinduced charge carrier separation in single domain nanoparticles using the depolarization field as a driving force is shown.
imageDeutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659Peer Reviewe
The Effect of Scandium Ternary Intergrain Precipitates in Al-Containing High-Entropy Alloys
We investigate the effect of alloying with scandium on microstructure, high-temperature phase stability, electron transport, and mechanical properties of the Al2CoCrFeNi, Al0.5CoCrCuFeNi, and AlCoCrCu0.5FeNi high-entropy alloys. Out of the three model alloys, Al2CoCrFeNi adopts a disordered CsCl structure type. Both of the six-component alloys contain a mixture of body-centered cubic (bcc) and face centered cubic (fcc) phases. The comparison between in situ high-temperature powder diffraction data and ex situ data from heat-treated samples highlights the presence of a reversible bcc to fcc transition. The precipitation of a MgZn2-type intermetallic phase along grain boundaries following scandium addition affects all systems differently, but especially enhances the properties of Al2CoCrFeNi. It causes grain refinement; hardness and electrical conductivity increases (up to 20% and 14% respectively) and affects the CsCl-type â fcc equilibrium by moving the transformation to sensibly higher temperatures. The maximum dimensionless thermoelectric figure of merit (ZT) of 0.014 is reached for Al2CoCrFeNi alloyed with 0.3 wt.% Sc at 650 °C
The Earlier the Better: Structural Analysis and Separation of Lanthanides with Pyrroloquinoline Quinone
Lanthanides (Ln) are critical raw materials, however, their mining and purification have a considerable negative environmental impact and sustainable recycling and separation strategies for these elements are needed. In this study, the precipitation and solubility behavior of Ln complexes with pyrroloquinoline quinone (PQQ), the cofactor of recently discovered lanthanide (Ln) dependent methanol dehydrogenase (MDH) enzymes, is presented. In this context, the molecular structure of a biorelevant europium PQQ complex was for the first time elucidated outside a protein environment. The complex crystallizes as an inversion symmetric dimer, Eu2PQQ2, with binding of Eu in the biologically relevant pocket of PQQ. LnPQQ and Ln1Ln2PQQ complexes were characterized by using inductively coupled plasma mass spectrometry (ICPâMS), infrared (IR) spectroscopy, 151EuâMössbauer spectroscopy, Xâray total scattering, and extended Xâray absorption fine structure (EXAFS). It is shown that a natural enzymatic cofactor is capable to achieve separation by precipitation of the notoriously similar, and thus difficult to separate, lanthanides to some extent