Craig A. Bridges

Conductive surface modification of LiFePO4 with nitrogen-doped carbon layers for lithium-ion batteries

The surface of rod-like LiFePO4 modified with a conductive nitrogen-doped carbon layer has been prepared using hydrothermal processing followed by post-annealing in the presence of an ionic liquid. The conductive surface modified rod-like LiFePO4 exhibits good capacity retention and high rate capability as the nitrogen-doped carbon layer improves conductivity and prevents aggregation of the rods during cycling.

High performance Cr, N-codoped mesoporous TiO2 microspheres for lithium-ion batteries

Cr, N-codoped TiO2 mesoporous microspheres have been successfully synthesized by a facile hydrothermal reaction followed by annealing under an ammonia atmosphere. Through introduction of Cr, the nitrogen doping level was increased from 2.81 at.% for N-doped TiO2 to 5.68 at.% for Cr, N-codoped TiO2, which improves the electrical conductivity of TiO2. When used as an anode for lithium-ion rechargeable batteries, the Cr, N-codoping TiO2 microspheres led to an enhanced performance of 159.6 mA h g−1 at 5 C with a drop of less than 1% after 300 cycles.

Orienting oxygen vacancies for fast catalytic reaction.

A strategy to enhance the catalytic activity at the surface of an oxide thin film is unveiled through epitaxial orientation control of the surface oxygen vacancy concentration. By tuning the direction of the oxygen vacancy channels (OVCs) in the brownmillerite SrCoO2.5 , a 100-fold improvement in the oxygen reduction kinetics is realized in an epitaxial thin film that has the OVCs open to the surface.

Tailored recovery of carbons from waste tires for enhanced performance as anodes in lithium-ion batteries

Morphologically tailored pyrolysis-recovered carbon black is utilized in lithium-ion battery anodes with improved capacity as a potential solution for adding value to waste tire-rubber-derived materials. Micronized tire rubber was digested in a hot oleum bath to yield a sulfonated rubber slurry that was then filtered, washed, and compressed into a solid cake. Carbon was recovered from the modified rubber cake by pyrolysis in a nitrogen atmosphere. The chemical pretreatment of rubber produced a carbon monolith with higher yield than that from the control (a fluffy tire-rubber-derived carbon black). The carbon monolith showed a very small volume fraction of pores of widths 3–5 nm, prominent nanoporosity (pore width < 2 nm), reduced specific surface area, and an ordered assembly of graphitic domains. Electrochemical studies revealed that the recovered-carbon-based anode had a higher reversible capacity than that of graphite. Anodes made with a sulfonated tire-rubber-derived carbon and a control tire-rubber-derived carbon exhibited an initial coulombic efficiency of 71% and 45%, respectively. The reversible capacity of the cell with the sulfonated tire rubber-derived carbon as the anode was 390 mA h g−1 after 100 cycles, with nearly 100% coulombic efficiency. Our success in producing a higher performance carbon material from waste tire rubber for potential use in energy storage applications adds a new avenue to tire rubber recycling.

Frustration of Magnetic and Ferroelectric Long-Range Order in Bi2Mn4/3Ni2/3O6

The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 A(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.

Neutron scattering in the proximate quantum spin liquid α-RuCl3

Quantum matter provides an effective vacuum out of which arise emergent particles not corresponding to any experimentally detected elementary particle. Topological quantum materials in particular have become a focus of intense research in part because of the remarkable possibility to realize Majorana fermions, with their potential for new, decoherence-free quantum computing architectures. In this paper we undertake a study on high-quality single crystal of -RuCl3 which has been identified as a material realizing a proximate Kitaev state, a topological quantum state with magnetic Majorana fermions. Four-dimensional tomographic reconstruction of dynamical correlations measured using neutrons is uniquely powerful for probing such magnetic states. We discover unusual signals, including an unprecedented column of scattering over a large energy interval around the Brillouin zone center which is remarkably stable with temperature. This is straightforwardly accounted for in terms of the Majorana excitations present in Kitaevs topological quantum spin liquid. Other, more delicate, features in the scattering can be transparently associated with perturbations to an ideal model. This opens a window on emergent magnetic Majorana fermions in correlated materials.Sighting of magnetic Majorana fermions? Quantum spin liquids—materials whose magnetic spins do not settle into order even at absolute zero temperature—have long captured the interest of physicists. A particularly lofty goal is finding a material that can be described by the so-called Kitaev spin model, a network of spins on a honeycomb lattice that harbors Majorana fermions as its excitations. Banerjee et al. present a comprehensive inelastic neutron scattering study of single crystals of the material α-RuCl3, which has been predicted to a host a Kitaev spin liquid. The unusual dependence of the data on energy, momentum, and temperature is consistent with the Kitaev model. Science, this issue p. 1055 Unusual inelastic neutron scattering signal is consistent with predictions of the Kitaev spin model. The Kitaev quantum spin liquid (KQSL) is an exotic emergent state of matter exhibiting Majorana fermion and gauge flux excitations. The magnetic insulator α-RuCl3 is thought to realize a proximate KQSL. We used neutron scattering on single crystals of α-RuCl3 to reconstruct dynamical correlations in energy-momentum space. We discovered highly unusual signals, including a column of scattering over a large energy interval around the Brillouin zone center, which is very stable with temperature. This finding is consistent with scattering from the Majorana excitations of a KQSL. Other, more delicate experimental features can be transparently associated with perturbations to an ideal model. Our results encourage further study of this prototypical material and may open a window into investigating emergent magnetic Majorana fermions in correlated materials.

Degradation mechanisms of lithium-rich nickel manganese cobalt oxide cathode thin films

This paper reports a method to prepare Li-rich NMC (Li1.2Mn0.55Ni0.15Co0.1O2) thin film cathodes for Li-ion batteries using RF magnetron sputtering and post-annealing in O2. Thin film cathodes with high reversible capacities (260 mA h g−1) and potential profiles similar to those of the powder material have been obtained. Structural and electrochemical studies show that the grown materials consist of a layered structure with trigonal symmetry in which Li/TM ordering is partially achieved. Using XPS we determine that the surface is comprised of Mn4+, Co3+ and Ni2+ cations inside an O2− framework. The loss mechanisms of these electrodes have been studied after 184 cycles. The data after cycling shows the absence of Li/TM ordering, confirming that Li2MnO3 activation is irreversible, while electron diffraction data indicates extensive structural modifications upon cycling. In addition, we identified that the surface chemistry is dominated by inorganic species (LiF, Lix′POy′Fz′, LixPFy), along with small amounts of organic species with C–O and O–CO groups such as PEO, LiOR and RCO2Li. Moreover, XPS results indicate that Ni and Co migrate into the bulk while the reduction of Mn4+ into Mn3+ is clearly evidenced, as expected from the activation of Li2MnO3 domains and discharging to 2.5 V.

Excitations in the field-induced quantum spin liquid state of α-RuCl3

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations. However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.Condensed Matter Physics: magnetic field drives spins to a liquidA sufficiently large magnetic field suppresses long-range magnetic order in α-RuCl3, leaving a disordered state with a gapped continuum spectrum of magnetic excitations, similar to that expected for the famous Kitaev quantum spin liquid. An international team led by Stephen E. Nagler from Oak Ridge National Laboratory in the USA performed time-of-flight neutron scattering to study low energy magnetic excitations of α-RuCl3. They observed that the application of a sufficiently large magnetic field to this material suppressed spin waves associated with the long-range order, and drove it to an unusual excited state. By comparison with calculations, these results are consistent with the Kitaev quantum spin liquid state in a magnetic field. The results provide important information of a possible route to producing gapped excitations related to magnetic Majorana Fermions towards topologically protected quantum computation.

Unconventional spin dynamics in the honeycomb-lattice material α-RuCl3 : High-field electron spin resonance studies

The honeycomb-lattice material

A POM–organic framework anode for Li-ion battery

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