A high-entropy alloy (HEA) of HfNbTiVZr was synthesized using an arc furnace followed by ball milling. The hydrogen absorption mechanism was studied by in situ X-ray diffraction at different ...temperatures and by in situ and ex situ neutron diffraction experiments. The body centered cubic (BCC) metal phase undergoes a phase transformation to a body centered tetragonal (BCT) hydride phase with hydrogen occupying both tetrahedral and octahedral interstitial sites in the structure. Hydrogen cycling of the alloy at 500 °C is stable. The large lattice strain in the HEA seems favorable for absorption in both octahedral and tetrahedral sites. HEAs therefore have potential as hydrogen storage materials because of favorable absorption in all interstitial sites within the structure.
Glass–ceramic solid electrolytes have been reported to exhibit high ionic conductivities. Their synthesis can be performed by crystallization of mechanically milled Li2S–P2S5 glasses. Herein, the ...amorphization process of Li2S–P2S5 (75:25) induced by ball milling was analyzed via X-ray diffraction (XRD), Raman spectroscopy, and 31P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Several structural building blocks such as P4S10, P2S64–, P2S74–, and PS43– occur during this amorphization process. In addition, high-temperature XRD was used to study the crystallization process of the mechanically milled Li2S–P2S5 glass. Crystallization of phase-pure β-Li3PS4 was observed at temperatures up to 548 K. The kinetics of crystallization was analyzed by integration of the intensity of the Bragg reflections. 7Li NMR relaxometry and pulsed field-gradient (PFG) NMR were used to investigate the short-range and long-range Li+ dynamics in these amorphous and crystalline materials. From the diffusion coefficients obtained by PFG NMR, similar Li+ conductivities for the glassy and heat-treated samples were calculated. For the glassy sample and the glass–ceramic β-Li3PS4 (calcination at 523 K for 1 h), a Li+ bulk conductivity σLi of 1.6 × 10–4 S/cm (298 K) was obtained, showing that for this system a well-crystalline material is not essential to achieve fast Li-ion dynamics. Impedance measurements reveal a higher overall conductivity for the amorphous sample, suggesting that the influence of grain boundaries is small in this case.
The atomistic mechanisms occurring during the processes of aging and rejuvenation in glassy materials involve very small structural rearrangements that are extremely difficult to capture ...experimentally. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in Cu
Zr
Al
Hf
Co
bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. Using a measure of the configurational entropy calculated from the X-ray pair correlation function, the structural footprint of the deformation-induced rejuvenation in bulk metallic glass is revealed. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. This opens hitherto unavailable experimental possibilities allowing to unambiguously correlate changes in atomic configuration and structure to calorimetrically observed signals and can attribute those to changes of the dynamic and vibrational relaxations (α-, β- and γ-transition) in glassy materials. The results suggest that the structural footprint of the β-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the β-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature γ-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.
Polymorphic phase transitions are common in crystalline solids. Recent studies suggest that phase transitions may also exist between two liquid forms with different entropy and structure. Such a ...liquid-liquid transition has been investigated in various substances including water, Al2O3-Y2O3 and network glass formers. However, the nature of liquid-liquid transition is debated due to experimental difficulties in avoiding crystallization and/or measuring at high temperatures/pressures. Here we report the thermodynamic and structural evidence of a temperature-induced weak first-order liquid-liquid transition in a bulk metallic glass-forming system Zr(41.2)Ti(13.8)Cu(12.5)Ni10Be(22.5) characterized by non- (or weak) directional bonds. Our experimental results suggest that the local structural changes during the transition induce the drastic viscosity changes without a detectable density anomaly. These changes are correlated with a heat capacity maximum in the liquid. Our findings support the hypothesis that the 'strong' kinetics (low fragility) of a liquid may arise from an underlying lambda transition above its glass transition.
In this work, Co66-xFexHf6.5B27.5 (x = 0, 10, 15, 20) metallic glasses (MGs) have been prepared by melt-spinning, and a comprehensive qualitative study including the atomic structure, thermal ...behavior, crystallization kinetics, and magnetic properties of the MGs is presented. The addition of Fe notably improves the thermal stability of the prepared glasses by increasing the width of the supercooled liquid region (SLR) from 26 K to 55 K. Analysis of the structure factor and the reduced-pair distribution function (PDF) reveal subtle variations in short-range ordering (SRO) and an increase of the atomic packing density of the glassy phase by 20 at% Fe addition. Notable rises in saturation polarization, Js, (from 0.21 T to 0.67 T), Curie point, Tc, (from 315 K to 530 K) and coercivity, Hc, (from 0.5 A/m to 2.5 A/m) are found after Fe alloying. The isothermal crystallization kinetics determined by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach demonstrate that the novel Co46Fe20Hf6.5B27.5 MG exhibits a remarkably higher activation energy and a significantly longer incubation time (about 16 min) before crystallization compared to existing Fe-free (x = 0) as well as most other Fe/Co-based MGs. Slight increases in Js (up to 5%) and Tc (about 4.7%), and a remarkable drop in Hc (up to 80%) are achieved for the Co46Fe20Hf6.5B27.5 MG upon isothermal annealing for a period of 3600 s. The attractive features such as high thermal stability, low coercivity of 0.5 A/m, and higher Js (up 0.7 T) compared to many Co-based glasses, make Co46Fe20Hf6.5B27.5 MG a promising soft magnetic material for future applications in power electronics, electric machines, and fabrication of large-size glassy samples by hot consolidation of MG particles.
•Soft magnetic Co66xFexHf6.5B27.5 (x = 0, 10, 15, 20) glasses were developed.•Fe addition notably improved the width of supercooled liquid region.•The atomic packing density of glassy phase increases by 20% Fe addition.•One of the longest incubation times before crystallization was obtained for x = 20.•A coercivity of 0.5 A/m was achieved for the relaxed glass with 20% Fe.
Synthetic steps leading to the preparation of a Schiff base and its complexation reactions with Co(II), Ni(II), Cu(II) and Pd(II) ions with corresponding colour changes.
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•Novel ...azo-azomethine-tetracarboxylic Shiff base (L2) was prepared and characterized.•L2 forms stable complexes with Co(II), Ni(II), Cu(II) and Pd(II) ions.•Prepared complexes were characterized in solution and solid-state.•UV–VIS titration and Job́s plot confirmed the formation of complexes in 1:1 (M(II):L2) stoichiometry.
Novel tetracarboxylic Schiff-base ligand, namely 5,5′-((1E,1′E)-(((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(4-hydroxy-3,1-phenylene))bis(diazene-2,1-diyl)) diisophthalic acid (L2) was prepared by the condensation reaction of ethane-1,2-diamine with 4-((3-formyl-4-hydoxyphenyl)diazenyl) isophthalic acid (L1) in anhydrous ethanol. A prepared organic compound is potential N,O-multidentate chelating ligand, which forms stable complexes with metal(II) ions in 1:1 up to 1:5 M ratio of the metal to ligand. Its reactions with corresponding nitrate salts have synthesized the complexes of L2 with Co(II) (1), Ni(II) (2), Cu(II) (3) and Pd(II) (4) ions. The prepared dye and its metal-containing complexes were investigated by the combination of elemental and ICP-MS analyses, infrared spectroscopy, thermal analysis, powder X-ray diffraction, 1H and 13C NMR and UV/VIS spectroscopy. UV/VIS titration measurements showed the stable formation of 1:1 Schiff-based complexes with four free carboxylic groups. Prepared metal-containing complexes are suitable linkers for metal–organic frameworks preparation with promising applications in gas storage and heterogeneous redox-catalysis.
The aim of the present work was to study the negative lattice expansion of the La(Fe,Si)13 phase in the LaFe11.2Co0.7Si1.1 alloy modified by Ce, Ho, Pr or Mn. The highest change of lattice constant ...was observed for sample doped with Ce, which was result of the first order phase transition, previously observed in this alloy. The gradual decrease of relative change of lattice parameter with increase of Mn content was detected. Furthermore, anomalous behavior of temperature dependence of lattice constant for α-Fe phase was also observed. The X-ray diffraction analysis showed that this phenomenom is caused by negative lattice expansion of the La(Fe,Si)13 phase.
•The anomalous behavior of temperature dependence of lattice constant for α-Fe was observed in LaFe11.2Co0.7Si1.1 alloy modified by Ce, Ho, Pr or Mn.•The gradual decrease of relative change of lattice parameter with increase of Mn content was detected.•The highest change of lattice constant was observed for sample doped with Ce.
Great interests on high temperature shape memory alloys (HTSMAs) are recently raised, driven primarily by the aerospace and automotive industries, for their potential to serve as solid state ...actuators at high temperatures over 373 K. Near equiatomic Ti-Ni conventional SMAs, as the most applied SMA system, were considered to possess appreciable shape memory effect and superelasticity only below 373 K, which owes to low martensitic transformation temperatures. Here we utilized the martensite stabilization effect and successfully expanded the viable zone of B19′ (monoclinic) martensite to 616 K in a 35% cold-rolled Ti-50Ni (CR35) SMA. After a training cycle, it exhibited quasi-linear superelasticity of narrow hysteresis, ~3% superelastic strain and high strength over 1.2 GPa in a wide temperature range up to 483 K. It is the first exploration of high temperature superelasticity associated with the stabilized martensite. Using transmission electron microscopy and in-situ heating/tensile synchrotron X-ray diffraction, we reveal the origin of martensite stabilization and the underlying mechanisms of unique superelasticity in the CR35. Our work provides an attractively facile approach to realize high temperature superelasticity in Ti-Ni conventional SMAs, as well as in other kinds of SMAs, for precise actuation within an expanded range of working temperature and stress.
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•High temperature superelasticity associated with stabilized martensite was achieved upto 483K in 35% cold rolled Ti-50Ni.•Superelasticity possesses quasi-linearity of narrow hysteresis, 3% strain and >1.2GPa strength in 185K temperature range.•Martensite stabilization in severely deformed Ti-50Ni is attributed to biased local stress fields of dislocation network.•Superelasticity originates from elasticity, reversible stress-induced B2➔B19’ transition and reorientation of B19’ domains.•We provide a facile approach to expand the working temperature and stress zones of superelasticity in shape memory alloys.
Metal-organic frameworks (MOFs) represent a class of nanoporous materials built up by metal ions and organic linkers with several interesting potential applications. The present study described the ...synthesis and characterization of Gd(III)-based MOF with the chemical composition Gd(BTC)(H2O)·DMF (BTC – trimesate, DMF = N,N′-dimethylformamide), known as MOF-76(Gd) for hydrogen adsorption/desorption capacity and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning and transmission electron microscopy. The crystal structure of MOF-76(Gd) consists of gadolinium (III) and benzene-1,3,5-tricarboxylate ions, one coordinated aqua ligand and one crystallization DMF molecule. The polymeric framework of MOF-76(Gd) contains 1D sinusoidally shaped channels with sizes of 6.7 × 6.7 Å propagating along c crystallographic axis. The thermogravimetric analysis, heating infrared spectroscopy and in-situ heating powder X-ray diffraction experiments of the prepared framework exhibited thermal stability up to 550 °C. Nitrogen adsorption/desorption measurement at −196 °C showed a BET surface area of 605 m2 g−1 and pore volume of 0.24 cm3 g−1. The maximal hydrogen storage capacity of MOF-76(Gd) was 1.66 wt % and 1.34 wt % −196 °C and −186 °C and pressure up to 1 bar, respectively. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Gd) is a suitable material for moisture sensing application with a fast response (11 s) and recovery time (2 s) in the relative humidity range of 11–98%.
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•A simple and effective method to synthesize Gd(III) MOF is presented.•Structural and Morphological properties are discussed.•Investigated its humidity sensing and gas adsorption properties.•H2 storage capacities at 77 K and pressure up to 20 bar are discussed.
Using synchrotron X-ray scattering, we investigate liquid Ge15Te85 spanning a wide temperature range from near Tg to the melt, and demonstrate that the density anomaly and fragile-strong transition ...are not only related to short-range-order (SRO) structural change (e.g. Peierls-like distortion), but also accompanied by a remarkable development of medium-range-order (MRO). The latter manifests as an emerging pre-peak in total structure factor S(Q) and atomic pair correlations on the length scale of ∼8 Å in the real space G(r) function. The results highlight the role of medium-range structural ordering in the evolution of the configurational entropy which, according to the Adam-Gibbs theory, can be linked to the fragile-strong transition (FS-transition). Based on the relation between structure and liquid dynamics, the FS-transitions at high pressures are examined in terms of experimental data and the Ehrenfest relation. This work identifies the length scale for the atomic correlations in MRO structural evolutions and presents a structural approach to exploring liquid dynamics, which may be useful for investigating relevant phase-change alloys.
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