Correlation between Li+ adsorption capacity and the preparation conditions of spinel lithium manganese precursor

Spinel lithium manganese oxides can be used as Li⁺ adsorbent with topotactical extraction of lithium. In this paper, the solid state methods were introduced to prepare spinel lithium manganese precursors with Li₂CO₃ and LiOH·H₂O as different Li sources. The Li⁺ uptake was studied to clarify the correction between Li⁺ adsorption capacity and the preparation conditions of precursors, including different Li sources, Li/Mn mole ratios and heating time. The results indicated that the Li⁺-extracted materials prepared with LiOH·H₂O and MnCO₃ usually have higher Li⁺ adsorption capacity than Li₂CO₃ and MnCO₃, and an ascending trend was found in Li⁺ uptake with increasing Li/Mn mole ratio in the preparation of the precursor, but it is not proportional. The Mn₂O₃ impurities could be the primary reason for decreasing Li⁺ adsorption capacity. Furthermore, it is concluded that the Li⁺-extracted materials obtained from spinel manganese oxides synthesized with Li/Mn = 1.0 can serve as selective Li⁺ absorbents due to its high selectivity and large adsorption capacity.     

Muon spin relaxation studies of extremely concentrated paramagnetic electrolyte solutions

The diamagnetic signal in aqueous solutions of non-reacting salts arises from muons substituted for protons in water molecules. For concentrated solutions of paramagnetic salts, muon spin relaxation results from the strong dipolar and scalar interactions between the paramagnetic ion and the muon. Information on dynamic and structural aspects of such solutions is derived from measurements of the transverse relaxation rate as a function of applied field over a wide range. Data are presented for concentrated solutions of Mn(NO₃)₂ and solutions of composition Mn _x Ca_(1–x (NO₃)₂·6H₂O.     

Electron spin resonance of diluted solid solutions of MnO2 in Y2O3

Electron spin resonance spectra of Mn²⁺ in diluted solid solutions of MnO₂ in Y₂O₃ have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn²⁺ ions in sites with two different symmetries were observed, as well as Mn²⁺ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn²⁺ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C₂ symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn²⁺ ions of 0.53 nm, of the same order as that of Mn²⁺ ions in CaO.     

Secondary-Phase Formation in Spinel-Type LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>-Cathode Materials for Lithium-Ion Batteries: Quantifying Trace Amounts of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> by Electron Paramagnetic Resonance Spectroscopy

Spinel-type lithium manganese oxides are considered as promising cathode materials for lithium-ion batteries. Trace amounts of Li₂MnO₃ usually occur as a secondary phase in lithium-manganese spinels in the common high-temperature, solid-state synthesis, affecting the overall Li–Mn stoichiometry in the spinel phase and thereby the electrochemical performance. However, the formation of Li₂MnO₃ lower than 1 wt.% can hardly be quantified by the conventional analytical techniques. In this work, we synthesized lithium-manganese spinels with different Li/Mn molar ratios and demonstrate that electron paramagnetic resonance (EPR) enables quantifying trace amounts of Li₂MnO₃ below 10^?2 wt.% in the synthesized products. The results reveal that the formation of Li₂MnO₃ secondary phase is favored by lithium excess in the synthesis. Based on the quantitative evaluation of the EPR data, precise determining Li–Mn stoichiometry in the spinel phase in Li_1+xMn_2?xO₄ materials can be assessed. Accordingly, it is possible to estimate the amount of lithium on 16d-sites in the Li-rich manganese spinels.     

The muon depolarization rate in β-palladium hydride

A depolarization rate σ = 0.1205 ± 0.0050 μsec^?1, due to the proton nuclear dipolar fields, was observed for polarized muons implanted in Pd-H_0.97 in the β phase, at temperatures below 50 K, independent of temperature and applied field. The results indicate that the muon substitutes for one of the protons, and that nearest-neighbor protons are at octahedral lattice sites. On comparing our results with recent NMR data, it appears that the mean muon-proton nearest neighbor distance is significantly larger than that between protons alone. Also, a search for muon local moment magnetism gave a null result.     

Synthesis and characterization of lithium manganese oxides with core-shell Li4Mn5O12@Li2MnO3 structure as lithium battery electrode materials

By a facile LiNO₃ flux method, lithium manganese oxide composites (xLi₄Mn₅O₁₂? yLi₂MnO₃) were synthesized using a hierarchical organization precursor of manganese dioxide. Li₄Mn₅O₁₂ and Li₂MnO₃ have spinel and rocksalt structures, respectively. The lithiation and structural transformation from the precursor to the composites occurred topotactically from exterior toward interior in the precursor particle with the increase of reaction time, and the composites had core-shell spinel@rocksalt structures in addition to the original hierarchical core-shell organization. The electrochemical measurements at 50 °C after 50 cycles confirmed that a typical spinel@rocksalt cathode had higher capacity retention (87.1%) than that with the composition close to the stoichiometric spinel (64.6%), indicating the Li₂MnO₃ shell can improve cycling stability for the composite electrode at elevated temperature.     

Dynamics of muons in the ferroelectric material KDP

Muon spin relaxation in zero field and longitudinal field was measured in single crystal samples of KH₂PO₄ (KDP) and KD₂PO₄ (DKDP) over a temperature range of 5 K to 300 K. At low temperatures, diamagnetic muons and muon substituted radicals with nuclear hyperfine coupling can be observed. For both KDP and DKDP, a minor change was observed in the dynamics of the muon below 140 K. Above 140 K, the mobility of the muon appears to increase and the diffusion rate becomes faster with increasing temperature. Only a small increase in the relaxation rate is observed in KDP due to the presence of theH ⁺, suggesting that the relaxation effects probably originate from the³¹P.     

Medium energy neutrinos from solar flares

The production of neutrinos with energies higher than 0.1 GeV in the solar atmosphere during solar flares is discussed. Neutrinos and muons are generated in decays of π^+- mesons produced in nuclear interactions of accelerated solar flare protons with matter of the Sun. Muons themselves decay yielding neutrinos. These neutrinos could come to the Earth and be detected with neutrino telescopes. Estimations of fluxes of such neutrinos are given.     

Luminescence and EPR spectroscopy of neutron-irradiated single crystals of magnesium aluminium spinel

Neutron irradiated single crystals of stoichiometric MgAl₂O₄ and MgAl₂O₄:Mn²⁺ (0.15 wt. %) were studied using the methods of luminescence spectroscopy and versions of electron paramagnetic resonance. In stoichiometric MgAl₂O₄:Mn²⁺ single crystals, the transition of a part of manganese impurity ions from tetrahedral to octahedral coordination, caused by irradiation with fast fission neutrons, is detected using photoluminescence spectra. This fact confirms the partial inversion of a normal spinel due to neutron-irradiation. Using pulse EPR technique it is shown that an electron in the field of oxygen vacancy (i.e. from neutron-irradiation induced F⁺ centres, which are spatially separated from each other) is in hyperfine interaction only with neighbouring ²⁷Al nuclei with nuclear spin 5/2.     

Do right-handed neutrinos exist?

The weak interaction of the four components of the muon is discussed. Using a high-energy pion beam as a source of polarized muons, the components μ^?_R or μ⁺_L can be selected and used in a sensative search for massive right-handed neutrinos. This search may be extended to higher mass by the use of colliding beams of protons and polarized electrons.     

Muon spin relaxation measurements of CsC60, RbC60, KC60

Muon spin relaxation (μ⁺SR) measurements of CsC₆₀ and RbC₆₀ have revealed magnetic ordering at 20 K and 15 K respectively, with static internal fields at the muon site of \sim7 G for both samples. No magnetic ordering is seen in KC₆₀ down to 2.5 K. An apparent small increase in muon spin relaxation which had been seen at 70 K in RbC₆₀ is ascribed to an extrinsic effect, originating in muons which stopped in the aluminum sample holder. This revised version was published online in July 2006 with corrections to the Cover Date.     

Proton magnetic relaxation in solutions of E. coli ribosomal RNA containing Mn2+ ions

A study has been made over a range of temperatures and magnetic field strengths of the spin relaxation of water protons in aqueous solutions of E. coli ribosomal RNA containing Mn²⁺ ions. The effects of the paramagnetic ions are enhanced in the presence of the RNA. As the temperature falls T ₁ passes through a minimum value, the magnitude of which is field dependent, and this is attributed to a change in dipolar relaxation mechanism from rotation of the aquocomplex to electron spin relaxation. The relevance of this work is assessed in relation to other work on proton relaxation enhancement in Mn²⁺-containing solutions of biopolymers.     

Indirect Raman identification of the proton insertion in the high‐temperature [Ba/Sr][Zr/Ti]O3‐modified perovskite protonic conductors

OH⁻ and H₃O⁺ species in hydrates and simple oxides are rather well characterised from their IR, Raman and inelastic neutron points of view. For the H⁺ (H₂O) species in solid state the variability is well established and assignment remains discussed. The question of the vibrational signature of isolated proton (e.g. the ionic proton, a proton sharing its interaction with more than two acceptors) and its dynamic nature (proton gas, polaron,…) is open. H⁺‐containing modified perovskites A(Ba,Sr,…) B(Zr,Ce,Ti,…) O₃ are potential ceramic membranes for fuel cell and medium temperature water electrolysis (300–800 °C). Comparison studies of the protonated and non‐protonated lanthanide/rare earth‐modified perovskites of type Ba(Sr)Zr(Ti)O₃ as well as Al‐modified BaTiO₃ show that a broad component centred at 2500 cm⁻¹ is observed after ‘proton insertion’. Its intensity is correlated to the protonic species content as well as to the conductivity of the materials. The mixed nature of this feature is discussed: fluorescence related to the dangling bonds, A, B, C bands or new phenomena related to the ionic protons and associated electronic defect. Copyright © 2008 John Wiley & Sons, Ltd.     

Measurement of17O quadrupole interactions and identification of the diamagnetic fraction in ice by muon level crossing resonance

By means of Level Crossing Resonance in a sample of ice which is enriched in H₂ ¹⁷O, the final diamagnetic state of implanted positive muons is determined to be the muonium-substituted molecule HMuO, accommodated in the regular and fully relaxed Ih structure. The¹⁷O quadrupole coupling constant is measured to be 6.1 MHz at 200 K assuming an asymmetry parameter close to unity, a decrease of about 5% relative to that in normal ice Ih at 77 K. The isotope effect is attributed to a greater polarization in the vicinity of a muonium (as opposed to a normal hydrogen) bond. At 50 K, an additional resonance is observed which could correspond to a precursor state, so far not definitely identified. One possibility is a muon trapped at a Bjerrum L-defect, giving a {H₂O−Mu−OH₂}⁺ species with an,¹⁷O quadrupole coupling constant of 8.2 MHz and asymmetry parameter of 0.55. Above this temperature, the fall in the (Gaussian) line-width parameter is attributed to the increasing rate of proton or muon migration, the correlation time dropping from 4 μs at 80 K to 1 μs near the melting-point. The increase in the diamagnetic fraction with rise in temperature is attributed to the increasing proportion of trapping sites available for muon capture.     

Direct muon production in proton-nuclear collisions at 70, 50 and 35 GeV

Direct muon yields (μ^±) in the transverse momentum range of 1.9–3.1 GeV/c on Cu and Be nuclei at the proton energies 70, 50 and 35 GeV have been measured. The yield of direct μ/π is shown to considerably decrease when proton energy varies from 70 to 35 GeV. The charge ratio of direct muon μ⁺/μ^? as well as the dependence of the yield of direct muons on the atomic number of the target have been measured.     

Materials for spintronic: Room temperature ferromagnetism in Zn–Mn–O interfaces

In this paper we study the room temperature ferromagnetism reported on Mn-doped ZnO and ascribed to spin polarization of conduction electrons. We experimentally show that the ferromagnetic behaviour is associated to the coexistence of Mn³⁺ and Mn⁺⁴ in MnO₂ grains where diffusion of Zn promotes the Mn⁴⁺→Mn³⁺ reduction. Potential uses of this material in spintronic devices are analysed.     

Computation of transverse muon-spin relaxation functions including trapping-detrapping reactions,with application to electron-irradiated tantalum

A new technique for the economical evaluation of transverse muon spin relaxation functions in situations involving μ⁺ trapping at and detrapping from crystal defects is applied to electron-irradiated Ta exhibiting relaxation maxima at about 35 K, 100 K, and 250 K. The longrange μ⁺ diffusion is shown to be limited by traps over the entire temperature range investigated. The (static) relaxation rates for several possible configurations of trapped muons are discussed, including the effect of the simultaneous presence of a proton in a vacancy. Work supported by the Bundesministerium für Forschung und Technologie, Bonn, Fed. Rep. of Germany     

Muon level crossing resonance of the R3NMu+ ion

Observation of muon level crossing resonance with¹⁴N nuclei in frozen triethylamine is reported and assigned to the ionic species (C₂H₅)₃NMu⁺. In forming this species, the implanted positive muons mimic the chemical behaviour of protons as usual, here in a process analogous to the protonation of a base. The resultant molecular ion has the axial symmetry necessary for detection of level crossing with an integral-spin nucleus. The quadrupole coupling constant is determined to be ¦e ² qQ/h¦=0.41(4) MHz, corresponding to an electric field gradient on¹⁴N of 0.10(1) a.u. and consistent with anab initio estimate for species of the type R₃NMu⁺. The prospects for detection of the muonium-substituted ammonium ion NH₃Mu⁺ ion in ammonia are discussed.     

First μ+SR studies on thin films with a new beam of low energy positive muons at energies below 20 keV

At the Paul Scherrer Institute slow positive muons (μ⁺) with nearly 100% polarization and an energy of about 10 eV are generated by moderation of an intense secondary beam of surface muons in an appropriate condensed gas layer. These epithermal muons are used as a source of a tertiary beam of tunable energy between 10 eV and 20 keV. The range of these muons in solids is up to 100 nm which allows the extension of the μ⁺SR techniques (muon spin rotation, relaxation, resonance) to the study of thin films. A basic requirement for the proper interpretation of μ⁺SR results on thin films and multi-layers is the knowledge of the depth distribution of muons in matter. To date, no data are available concerning this topic. Therefore, we investigated the penetration depth of μ⁺ with energies between 8 keV and 16 keV in Cu/SiO₂ samples. The experimental data are in agreement with simulated predictions. Additionally, we present two examples of first applications of low energy μ⁺ in μ⁺SR investigations. We measured the magnetic field distribution inside a 500-nm thin High-T_C superconductor (YBa₂Cu₃O_7-δ), as well as the depth dependence of the field distribution near the surface. In another experiment a 500-nm thin sample of Fe-nanoclusters (diameter 2.4(4) nm), embedded in an Ag matrix with a volume concentration of 0.1%, was investigated with transverse field μ⁺SR. This revised version was published online in August 2006 with corrections to the Cover Date.