Elucidating local diffusion dynamics in nickel-rich layered oxide cathodes.

Elucidating Li-ion transport properties is essential for designing suitable methodologies to optimise electrochemical performance in Ni-rich cathodes for high energy density Li-ion batteries. Here, we report the local-scale Li-diffusion characteristics of a series of nickel-rich layered oxide cathodes, prepared via microwave methods, using muon spin relaxation methods. Our results detail the effects of cation dopants, selected for structure stability, on transport properties in candidate nickel-rich chemistries. We find that the local diffusion properties improve with increasing nickel content. Our results demonstrate that these observations are dependant on substitutional effects.

Magnetic Field Induced Quantum Spin Liquid in the Two Coupled Trillium Lattices of K_{2}Ni_{2}(SO_{4})_{3}.

Quantum spin liquids are exotic states of matter that form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of K_{2}Ni_{2}(SO_{4})_{3} forming a three-dimensional network of Ni^{2+} spins. Using density functional theory calculations, we show that this network consists of two interconnected spin-1 trillium lattices. In the absence of a magnetic field, magnetization, specific heat, neutron scattering, and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field B≳4 T diminishes the ordered component and drives the system into a pure quantum spin liquid state. This shows that a system of interconnected S=1 trillium lattices exhibits a significantly elevated level of geometrical frustration.

Signatures of a Spin-1/2 Cooperative Paramagnet in the Diluted Triangular Lattice of Y_{2}CuTiO_{6}.

We present a combination of thermodynamic and dynamic experimental signatures of a disorder driven dynamic cooperative paramagnet in a 50% site diluted triangular lattice spin-1/2 system: Y_{2}CuTiO_{6}. Magnetic ordering and spin freezing are absent down to 50 mK, far below the Curie-Weiss scale (-θ_{CW}) of ∼134 K. We observe scaling collapses of the magnetic field and temperature dependent magnetic heat capacity and magnetization data, respectively, in conformity with expectations from the random singlet physics. Our experiments establish the suppression of any freezing scale, if at all present, by more than 3 orders of magnitude, opening a plethora of interesting possibilities such as disorder stabilized long range quantum entangled ground states.

Evaluating lithium diffusion mechanisms in the complex spinel Li2NiGe3O8.

Lithium-ion diffusion mechanisms in the complex spinel Li2NiGe3O8 have been investigated using solid-state NMR, impedance, and muon spectroscopies. Partial occupancy of migratory interstitial 12d sites is shown to occur at lower temperatures than previously reported. Bulk activation energies for Li+ ion hopping range from 0.43 ± 0.03 eV for powdered samples to 0.53 ± 0.01 eV for samples sintered at 950 °C for 24 h, due to the loss of Li during sintering at elevated temperatures. A lithium diffusion coefficient of 3.89 × 10-12 cm2 s-1 was calculated from muon spectroscopy data for Li2NiGe3O8 at 300 K.

Quantum Spin Liquid from a Three-Dimensional Copper-Oxalate Framework.

The quantum spin liquid (QSL) state is of great interest in relation to quantum computation and superconductivity and the search for new QSL materials is a current challenge in chemistry. Existing inorganic and molecular QSL compounds have two-dimensional structures, with spins arranged on triangular and kagome lattices, whereas three-dimensional structures with QSL characteristics are rare. In the copper-oxalate framework compound [(C2H5)3NH]2Cu2(C2O4)3, Cu(II) is coordinated with three bisbidentate oxalate bridges to form a three-dimensional (10,3) lattice and this produces a strong antiferromagnetic interaction between Cu2+ (S = 1/2) atoms (θ = -180 K). No long-range ordering (LRO) was observed in either magnetic susceptibility or specific heat measurements down to 2 K. Absence of LRO was further confirmed by µSR measurements down to 60 mK, indicating that it is a gapless QSL with f > 3000. Due to Jahn-Teller distortion and partial dimerization, the effective dimensionality of the magnetic lattice is reduced. This compound nevertheless highlights the great potential for obtaining QSLs of varying dimensionality from metal-organic frameworks.

Long-term Health-related Quality of Life Following Esophagectomy: A Nonrandomized Comparison of Thoracoscopically Assisted and Open Surgery.

OBJECTIVE: The aim of this study was to assess long-term health-related quality of life (HRQL) in patients after thoracoscopic and open esophagectomy. SUMMARY OF BACKGROUND DATA: Trials comparing minimally invasive with open transthoracic esophagectomy have shown improved short-term outcomes; however, long-term HRQL data are lacking. This prospective nonrandomized study compared HRQL and survival after thoracoscopically assisted McKeown esophagectomy (TAMK) and open transthoracic Ivor Lewis esophagectomy (TTIL) for esophageal or gastroesophageal junction (GEJ) cancer. METHODS: Patients with esophageal or GEJ cancer selected for TAMK or TTIL completed baseline and follow-up HRQL assessments for up to 24 months using the EORTC generic and disease-specific measures, QLQ-C30 and QLQ-OES18. Baseline clinical variables were examined between the treatment groups and changes in mean HRQL scores over time estimated and tested using generalised estimating equations with propensity score (generated by boosted regression) adjustment. RESULTS: Of the 487 patients, 377 underwent TAMK and 110 underwent TTIL. Most clinical variables were similar in the 2 groups; however, there were significantly more patients with AJCC stage 3 disease who underwent TTIL than TAMK (54% vs 32%, P < 0.01) and this was reflected in the survival data.Mean symptom scores for pain were significantly higher in the TTIL group than in TAMK for 2 years postoperatively (P = 0.036). In addition, mean constipation scores were significantly higher for the TTIL group, with a 15-point difference in mean score at 3 months postoperatively (P = 0.037). CONCLUSIONS: This large comprehensive nonrandomized analysis of longitudinal HRQL shows that TTIL is associated with more pain and constipation than TAMK.

Quantum Griffiths Phase Inside the Ferromagnetic Phase of Ni_{1-x}V_{x}.

We study by means of bulk and local probes the d-metal alloy Ni_{1-x}V_{x} close to the quantum critical concentration, x_{c}≈11.6%, where the ferromagnetic transition temperature vanishes. The magnetization-field curve in the ferromagnetic phase takes an anomalous power-law form with a nonuniversal exponent that is strongly x dependent and mirrors the behavior in the paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous magnetic order and indicate the presence of dynamic fluctuating magnetic clusters. These results provide strong evidence for a quantum Griffiths phase on the ferromagnetic side of the quantum phase transition.

Muon Spin Relaxation Evidence for the U(1) Quantum Spin-Liquid Ground State in the Triangular Antiferromagnet YbMgGaO_{4}.

Muon spin relaxation (µSR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO_{4} indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the µ^{+} spin relaxation rates, which are proportional to the dynamic correlation function of the Yb^{3+} spins, exhibit temperature-independent plateaus. All these µSR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO_{4}.

Studies of a Large Odd-Numbered Odd-Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8 Mn.

The spin dynamics of Cr8 Mn, a nine-membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8 Mn is a rare example of a large odd-membered AF ring, and has an odd-number of 3d-electrons present. Odd-membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated-spin ground states. The chemical synthesis and structures of two Cr8 Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (µSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that µSR is sensitive to the ground-spin-state crossing from S=1/2 to S=3/2 in Cr8 Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin-pair correlations and scalar-spin chirality, shows a non-collinear spin structure that fluctuates between non-planar states of opposite chiralities.

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine).

The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3), and NCS (4)) were determined by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]EF6 (E = P, Sb), which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggered packing of adjacent layers. Long-range antiferromagnetic (AFM) order occurs below 1.5 (Cl), 1.9 (Br and NCS), and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3, and 4 were measured by electron-spin resonance with no evidence for zero-field splitting (ZFS) being observed. The magnetism of 1-4 spans the spectrum from quasi-two-dimensional (2D) to three-dimensional (3D) antiferromagnetism. Nearly identical results and thermodynamic features were obtained for 2 and 4 as shown by pulsed-field magnetization, magnetic susceptibility, as well as their Néel temperatures. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. Compound 3 is characterized as a 3D AFM with the interlayer interaction (J⊥) being slightly stronger than the intralayer interaction along Ni-pyz-Ni segments (J(pyz)) within the two-dimensional [Ni(pyz)2](2+) square planes. Regardless of X, J(pyz) is similar for the four compounds and is roughly 1 K.

Polymorphism control of superconductivity and magnetism in Cs(3)C(60) close to the Mott transition.

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition, which is governed by the role of electron correlations characteristic of high-temperature superconducting materials other than fullerides.

Ambient temperature and lung function in children with asthma in Australia.

The association between ambient temperature and lung function in children with asthma is still uncertain. A panel of 270 children (aged 7-12 years) with asthma was recruited from six Australian cities. They performed three successive forced expiratory manoeuvres twice daily for 4 weeks. The highest peak expiratory flow rate (PEF) and forced expiratory volume in 1 s (FEV1) were stored for each session. During the same period, data were obtained daily on ambient temperature, relative humidity and air pollution. Mixed models were used to examine the effects of temperature on lung function, controlling for individual characteristics and environmental factors. Ambient temperature was negatively related to both morning and evening PEF and FEV1 for 0-3 days lag. In general, the effects of temperature were stronger in males than in females for evening PEF, while the effects were stronger in females for evening FEV1. Children with asthma living in southern cities were more sensitive to high temperature than those in the northernmost city. Higher ambient temperature is associated with lower lung function in children with asthma. Preventive health policies will be required to protect children with asthma from increasingly frequent high temperatures.

Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer.

The discovery of high-temperature superconductivity in a layered iron arsenide has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the chemical composition of the spacer layer between adjacent anionic iron arsenide layers. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li(+), Na(+), K(+), Ba(2+)) or PbO- or perovskite-type oxide layers, and also in Fe(1.01)Se (ref. 8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Li(x)(NH(2))(y)(NH(3))(1-y)Fe(2)Se(2) (x~0.6; y~0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1) K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family.

An Australian national panel study of diurnal temperature range and children's respiratory health.

BACKGROUND: It is still uncertain whether diurnal temperature range (DTR) affects children's respiratory function. OBJECTIVE: To examine the effects of DTR on lung function and respiratory symptoms for school children with asthma in Australia. METHODS: A panel of 270 children (ages 7-12 years) with asthma living in 6 Australian cities was recruited. They were asked to perform 3 successive forced expiratory maneuvers using a portable electronic peak flow meter twice daily for 4 weeks. The highest values for peak expiratory flow (PEF) were stored for each session. At the same time, they were asked to record their respiratory symptoms (eg, cough and/or phlegm and wheeze and/or chest tightness) every day in the morning (for nighttime symptoms) and evening (for daytime symptoms). Daily data on different metrics of ambient temperature and air pollution were obtained from fixed monitors nearby. Relative humidity data were downloaded from the Weather Underground website. Mixed models, adjusting for children's individual characteristics and air pollution, were used to examine the effects of DTR on PEF and respiratory symptoms. RESULTS: DTR had linear effects on PEF and respiratory symptoms. An increase in DTR induced a reduction in PEF and increased the occurrence of respiratory symptoms. In general, the effects lasted for 3 days (lag, 0-2 days). The effects occurred for both boys and girls. CONCLUSION: Our findings provide evidence that DTR had significant effects on lung function and respiratory symptoms for children with asthma. These results indicate that it is important and necessary to protect children with asthma from the effect of unstable weather.

Are children׳s asthmatic symptoms related to ambient temperature? A panel study in Australia.

OBJECTIVES: To examine the short-term effects of ambient temperature on respiratory symptoms for school children with asthma across Australia. METHODS: A panel of 270 children (7-12 years) with asthma was recruited from six Australian cities. They were asked to record their respiratory symptoms every day in the morning (for night-time symptoms) and evening (for daytime symptoms) for four weeks. Daily ambient temperature, relative humidity and air pollution data were obtained from fixed monitors nearby. A mixed logistic regression model was used to examine the effects of ambient temperature on respiratory symptoms adjusted for children's sex, age, standing height, weight and air pollution. Subjects were specified as random effects. RESULTS: The relationships between ambient temperature and respiratory symptoms were linear. Increasing temperatures induced the risks of children's asthmatic symptoms, especially for "wheeze/chest tightness" and to a lesser extent for "cough/phlegm". The effects were acute and lasted for four days (lag 0-3) in general. With increasing ambient temperature, boys were more at risk than girls. CONCLUSIONS: High ambient temperature is a risk factor for respiratory symptoms in children with asthma. As ambient temperature increases, policies and strategies for rising temperatures will be necessary to protect asthmatic children.

Spatially homogeneous ferromagnetism below the enhanced Curie temperature in EuO(1-x) thin films.

We have used low-energy implanted muons as a volume sensitive probe of the magnetic properties of EuO(1-x) thin films. We find that static and homogeneous magnetic order persists up to the elevated T(C) in the doped samples, and the muon signal displays the double dome feature also observed in the sample magnetization. Our results appear incompatible with either the magnetic phase separation or bound magnetic polaron descriptions previously suggested to explain the elevated T(C), but are compatible with an RKKY-like interaction mediating magnetic interactions above 69 K.

Properties of new magnetic surfactants.

This Article describes the synthesis and detailed characterization of a new set of magnetic surfactants containing lanthanide metal counterions. SQUID magnetometry has been used to elucidate the magnetic phase behavior, and small-angle neutron scattering (SANS) provides evidence of micellar aggregation in aqueous media. This study also reveals that for cationic surfactants in aqueous systems there appears to be no significant increase in magnetic susceptibility after micellization.

Proteinase K-catalyzed synthesis of linear and star oligo(L-phenylalanine) conjugates.

Chemoenzymatic synthesis of peptides is a green and clean chemical reaction that offers high yields without using organic synthesis and serves as an alternative to traditional peptide synthesis methods. This report describes the chemoenzymatic synthesis of oligo(L-phenylalanine) mediated by proteinase K from Tritirachium album, which is one of the most widely used proteases in molecular biological studies. The synthesized linear oligo-phenylalanine showed a unique self-assembly in aqueous solutions. To further functionalize linear oligo(L-phenylalanine) as a low-molecular-weight gelator, it was cosynthesized with tris(2-aminoethyl)amine to obtain star-oligo(L-phenylalanine), which was bioconjugated to demonstrate its self-assembly into fluorescent fibers. The self-assembled fibers of star-oligo(L-phenylalanine) formed fibrous networks with various branching ratios, which depended on the molecular weights and molecular aspect ratios of star-oligo(L-phenylalanine). This is the first study to demonstrate that proteinase K is a suitable enzyme for chemoenzymatic cosynthesis of oligopeptides and star-shaped heteropeptides.

Direct Observation of Dynamic Lithium Diffusion Behavior in Nickel-Rich, LiNi0.8Mn0.1Co0.1O2 (NMC811) Cathodes Using Operando Muon Spectroscopy.

Ni-rich layered oxide cathode materials such as LiNi0.8Mn0.1Co0.1O2 (NMC811) are widely tipped as the next-generation cathodes for lithium-ion batteries. The NMC class offers high capacities but suffers an irreversible first cycle capacity loss, a result of slow Li+ diffusion kinetics at a low state of charge. Understanding the origin of these kinetic hindrances to Li+ mobility inside the cathode is vital to negate the first cycle capacity loss in future materials design. Here, we report on the development of operando muon spectroscopy (µSR) to probe the Å-length scale Li+ ion diffusion in NMC811 during its first cycle and how this can be compared to electrochemical impedance spectroscopy (EIS) and the galvanostatic intermittent titration technique (GITT). Volume-averaged muon implantation enables measurements that are largely unaffected by interface/surface effects, thus providing a specific characterization of the fundamental bulk properties to complement surface-dominated electrochemical methods. First cycle measurements show that the bulk Li+ mobility is less affected than the surface Li+ mobility at full depth of discharge, indicating that sluggish surface diffusion is the likely cause of first cycle irreversible capacity loss. Additionally, we demonstrate that trends in the nuclear field distribution width of the implanted muons during cycling correlate with those observed in differential capacity, suggesting the sensitivity of this µSR parameter to structural changes during cycling.

In Situ Diffusion Measurements of a NASICON-Structured All-Solid-State Battery Using Muon Spin Relaxation.

In situ muon spin relaxation is demonstrated as an emerging technique that can provide a volume-averaged local probe of the ionic diffusion processes occurring within electrochemical energy storage devices as a function of state of charge. Herein, we present work on the conceptually interesting NASICON-type all-solid-state battery LiM2(PO4)3, using M = Ti in the cathode, M = Zr in the electrolyte, and a Li metal anode. The pristine materials are studied individually and found to possess low ionic hopping activation energies of ∼50-60 meV and competitive Li+ self-diffusion coefficients of ∼10-10-10-9 cm2 s-1 at 336 K. Lattice matching of the cathode and electrolyte crystal structures is employed for the all-solid-state battery to enhance Li+ diffusion between the components in an attempt to minimize interfacial resistance. The cell is examined by in situ muon spin relaxation, providing the first example of such ionic diffusion measurements. This technique presents an opportunity to the materials community to observe intrinsic ionic dynamics and electrochemical behavior simultaneously in a nondestructive manner.