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Comparing Magnetism in Isostructural Oxides A0.8La1.2MnO4.1: Anisotropic Spin Glass (A = Ba) Versus Long Range Order (A = Sr)
No full textThis study presents the strikingly distinct magnetic properties of two isostructural compounds, Ba0.8La1.2MnO4.1 and Sr0.8La1.2MnO4.1 (K2NiF4 – type, I4/mmm). Spectroscopic studies have shown that Mn is in a +3.0(1) oxidation state only, in both compounds; therefore, the charge is balanced by accommodating extra oxygen at interstitials sites, as confirmed by neutron powder diffraction. We found that the Ba compound exhibits an exceedingly rare anisotropic spin glass behaviour, Tg = 26.4 K, with the moment freezing along the c-axis only while the in-plane spin components remain dynamic well below Tg. Experimental results including neutron diffraction, heat capacity, and magnetic (dc and ac) measurements performed on an oriented single crystal support this conclusion. This is a remarkable result, the only other known example of an anisotropic spin glass being Fe2TiO5. The spin glass state in Ba0.8La1.2MnO4.1 is argued to arise due to competing antiferromagnetic and ferromagnetic 180º Mn3+−O−Mn3+ superexchange interactions. In contrast, the Sr analogue shows 2D antiferromagnetic correlations and long range antiferromagnetic order below 95 K with a remarkably reduced ordered moment of 1.4 μB/Mn3+ instead of the ~ 4 μB expected for an S = 2 ion
Decomposition of single-source precursors under high-temperature high-pressure to access osmium–platinum refractory alloys
No full textOrder–disorder transition in nano-rutile TiO anodes: a high capacity low-volume change Li-ion battery material
No full textNano-sized particles of rutile TiO is a promising material for cheap high-capacity anodes for Li-ion batteries. It is well-known that rutile undergoes an irreversible order–disorder transition upon deep discharge. However, in the disordered state, the LiTiO material retains a high reversible ion-storage capacity of >200 mA h g. Despite the promising properties of the material, the structural transition and evolution during the repeated battery operation has so far been studied only by diffraction-based methods, which only provide insight into the part that retains some long-range order. Here, we utilize a combination of ex situ and operando total scattering with pair distribution function analysis and transmission electron microscopy to investigate the atomic-scale structures of the disordered LiTiO forming upon the discharge of nano-rutile TiO as well as to elucidate the phase behavior in the material during the repeated charge–discharge process. Our investigation reveals that nano-rutile upon Li-intercalation transforms into a composite of ∼5 nm domains of a layered LiTiO-type structure with ∼1 nm LiTiO grain boundaries with a columbite-like structural motif. During repeated charge–discharge cycling, the structure of this composite is retained and stores Li through a complete solid–solution transition with a remarkably small volume change of only 1 vol%
Kinetics of pressure-induced nanocrystal superlattice formation
No full textColloidal nanocrystals (NC) are known to self-organize into superlattices that promise many applications ranging from medicine to optoelectronics. Recently, the formation of high-quality PEGylated gold NC was reported at high hydrostatic pressure and high salt concentrations. Here, we study the formation kinetics of these superlattices after pressure jumps beyond their crystallisation pressure by means of small-angle X-ray scattering with few ms experimental resolution. The timescale of NC formation was found to be reduced the larger the width of the pressure jump. This is connected to an increase of crystal quality, i.e., the faster the NC superlattice forms, the better the crystal quality. In contrast to the formation kinetics, the melting of the NC superlattice is approximately one order of magnitude slower and shows linear kinetics
Understanding the Lithium Storage Mechanism in Core–Shell Hollow Nanospheres Derived from Metal–Organic Frameworks: An In operando Synchrotron Radiation Diffraction and in operando X-ray Absorption Spectroscopy Study
No full textIn this work, a core−shell structure of an Fe2O3@C hollow nanosphere derived from metal−organic frameworks is used as an anode material for Li-ion batteries. This material delivers a reversible capacity of 928 mAh g−1 at 0.2 A g−1 in 1 M LiPF6 in ethylene carbonate/dimethyl carbonate = 1:1. Although 1 M lithium bis(trifluoromethane sulfonyl)imide is used as a conductive salt, it delivers only 644 mAh g−1 at 0.2 A g−1. In operando synchrotron radiation diffraction revealed that the intermediate phases LixFe2O3 (R3̅m, hexagonal) and LixFe2O3 (Fd3̅m, Li-lean) form and subsequently convert to LixFe2O3 (Fd3̅m, Li-rich), which finally transforms into Fe, Li2O, and LixFe2O3 (Fd3̅m, X phase). During the delithiation process, the material does not return to the initial Fe2O3 structure; instead, the partially delithiated Lix−1Fe2O3 (Fd3̅m, X phase) and an amorphous metallic Fe phase remain. The Fe K-edge transition and the formation of Fe are confirmed by the in operando X-ray absorption spectroscopy measurement. Furthermore, the resistive contributions of this material in the two types of Li-salts are evaluated by electrochemical impedance spectroscopy, which highlights a different type of solid electrolyte interphase induced by the salt. This work provides fundamental insights into understanding the lithium-ion storage mechanism in conversion-type electrodes
A fungal family of lytic polysaccharide monooxygenase-like copper proteins
No full textLytic polysaccharide monooxygenases (LPMOs) are copper-containing enzymes that play a key role in the oxidative degradation of various biopolymers such as cellulose and chitin. While hunting for new LPMOs, we identified a new family of proteins, defined here as X325, in various fungal lineages. The three-dimensional structure of X325 revealed an overall LPMO fold and a His brace with an additional Asp ligand to Cu(II). Although LPMO-type activity of X325 members was initially expected, we demonstrated that X325 members do not perform oxidative cleavage of polysaccharides, establishing that X325s are not LPMOs. Investigations of the biological role of X325 in the ectomycorrhizal fungus Laccaria bicolor revealed exposure of the X325 protein at the interface between fungal hyphae and tree rootlet cells. Our results provide insights into a family of copper-containing proteins, which is widespread in the fungal kingdom and is evolutionarily related to LPMOs, but has diverged to biological functions other than polysaccharide degradation
The transverse momentum spectrum of low mass Drell-Yan production at next-to-leading order in the parton branching method
No full textThe transverse momentum spectrum of low mass Drell-Yan (DY) production at low center-of-mass energies is calculated by applying transverse momentum dependent (TMD) parton distributions obtained from the Parton Branching (PB) evolution method, combined with the next-to-leading-order (NLO) calculation of the hard process in the MCatNLO method. We compare our predictions with experimental measurements at low DY mass, and find very good agreement. In addition we use the low mass DY measurements at low to determine the width of the intrinsic Gauss distribution of the PB-TMDs at low evolution scales. We find values close to what has earlier been used in applications of PB-TMDs to high-energy processes at the Large Hadron Collider (LHC) and HERA. We find that at low DY mass and low even in the region of the contribution of multiple soft gluon emissions (included in the PB-TMDs) is essential to describe the measurements, while at larger masses () and LHC energies the contribution from soft gluons in the region of is small
Time- and momentum-resolved photoemission studies using time-of-flight momentum microscopy at a free-electron laser
No full textTime-resolved photoemission with ultrafast pump and probe pulses is an emerging technique with wide application potential. Real-time recording of nonequilibrium electronic processes, transient states in chemical reactions, or the interplay of electronic and structural dynamics offers fascinating opportunities for future research. Combining valence-band and core-level spectroscopy with photoelectron diffraction for electronic, chemical, and structural analyses requires few 10 fs soft X-ray pulses with some 10 meV spectral resolution, which are currently available at high repetition rate free-electron lasers. We have constructed and optimized a versatile setup commissioned at FLASH/PG2 that combines free-electron laser capabilities together with a multidimensional recording scheme for photoemission studies. We use a full-field imaging momentum microscope with time-of-flight energy recording as the detector for mapping of 3D band structures in (kx, ky, E) parameter space with unprecedented efficiency. Our instrument can image full surface Brillouin zones with up to 7 Å−1 diameter in a binding-energy range of several eV, resolving about 2.5 × 105 data voxels simultaneously. Using the ultrafast excited state dynamics in the van der Waals semiconductor WSe2 measured at photon energies of 36.5 eV and 109.5 eV, we demonstrate an experimental energy resolution of 130 meV, a momentum resolution of 0.06 Å−1, and a system response function of 150 fs