Search

In 1996 we initiated a study to evaluate several techniques for measuring light under broadleaf canopies. Hourly average photosynthetic photon flux density and percent transmittance were measured 1 m above the ground at four points in each of three canopy densities created by a spacing experiment in a 35-year-old paper birch (Betula papyrifera Marsh.) dominated stand located near Prince George, B.C. At each point, fisheye photographs were taken and LAI-2000 plant canopy analyzer (LAI-2000), spherical densiometer, and competition index (Lorimer'sindex) measurements were made. Percent transmittance measurements onan overcast day (1-h average), transmittance measured over periods of 3 h or longer on a clear day, LAI-2000 diffuse noninterceptance measurements, and gap light index determined from fisheye photographs were strongly correlated with growing season percent transmittance (r2>= 0.96) as was competition index (r2 = 0.928). Concave spherical densiometer measurements and midday percent transmittance measurements on clear days were also well correlated with measured percent transmittance (r2>= 0.89). Estimates of understory light by the LITE model were strongly correlated with growing season percent transmittance. Correlations improved with increasing length of the period simulated (r2 = 0.755 for a point measurement on a clear day; r2 = 0.936 for an entire sunny day;and, r2 = 0.953 for the entire growing season). However, this version of the model underestimated percent transmittance in these spaced birch stands by 34-90%. [ABSTRACT FROM AUTHOR]

Abstract: The structural properties of LiFePO4 prepared by the hydrothermal route and chemically delithiated have been studied using analytical electron microscopy and Raman spectroscopy. High-resolution transmission electron microscopy and selected area electron diffraction measurements indicate that the partially delithiated particles include LiFePO4 regions with cross-sections of finite size along the ac-plane, as a result of tilt grain boundary in the bc-plane, and dislocations in other directions. Only the boundary along the bc-plane is accompanied by a disorder over about 2nm on each side of the boundary. The Raman spectrum shows the existence of both LiFePO4 and FePO4 phases in the shell of the particles at a delithiation degree of 50%, which invalidates the core–shell model. This result also invalidates the recent model according to which each particle would be single-domain, i.e. either a LiFePO4 particle or a FePO4 particle. On the other hand, our results, like prior ones, can be understood within the framework of a model similar to the spinodal decomposition of a two-phase system, which is discussed within the framework of morphogenesis of patterns in systems at equilibrium. Both end-members, however, are well crystallized, suggesting a recovery similar to that observed in superplastic alloys, with dynamics that are due to the motion of nucleation fronts and dislocations, and not due to a diffusion phenomenon associated with a concentration gradient. [Copyright &y& Elsevier]

Abstract: Li x FePO4 glasses have been prepared by fast-quenching method in the whole range of composition 0 ⩽ x ⩽ 1. The amorphous state of glassy materials is confirmed by X-ray diffraction. Information concerning the local environment of Li and Fe cations and the configuration of (PO4)3− oxo-anions is obtained by Fourier transform infrared (FTIR) spectroscopy. While the LiFePO4 crystalline materials undergo a transition from the paramagnetic to the antiferromagnetic ordering at 52K, no magnetic ordering is observed in the vitreous samples that realize random field systems, so that a spin glass-like freezing is observed at low temperature. The paramagnetic Curie temperature of Li x FePO4 is independent of x and shifted to θ =−60K in the glassy state, due to a significant distortion of the FeO6 octahedra that alters the superexchange path inside the atomic FeO4 layers of the crystallized structure. On another hand, the PO4 tetrahedra are not significantly distorted in the glassy phase. The results are compared with highly disordered, but nanocrystallized LiFePO4 recently obtained at the early stage of synthesis by solid state reaction at 300°C. In this latter case, the lack of long-range antiferromagnetic ordering is due to substitutional disorder among the cationic sublattice. [Copyright &y& Elsevier]

Abstract: Currently, LiFePO4 is considered a good candidate as a positive electrode in rechargeable lithium-ion batteries for hybrid-electric vehicle (HEV) applications. A major difficulty with the preparation of the olivine structure (LiFePO4) comes from the existence of two oxidation states of iron, namely Fe(II) and Fe (III). Careful control of the synthesis procedure is needed to avoid any impurity which can poison the electrochemistry of LiFePO4 electrodes in Li-ion batteries. Analysis of the structure and morphology of the phospho-olivine LiFePO4 is presented as a function of the synthetic conditions. The combination of analytical methods, i.e. magnetization, M(H), susceptibility, χ m (T), and Raman scattering spectroscopy, appears to be a powerful tool for the detection of small amount of impurities. The electrochemical performance of optimized LiFePO4 is evaluated in Li4Ti5O12/LiPF6-EC-DEC/C-LiFePO4 cells operating at high temperature (60 °C). [Copyright &y& Elsevier]

Abstract: The layered LiNi0.5Mn0.5O2 was synthesized by wet-chemical method and characterized by X-ray diffraction and SQUID magnetometry. The powders adopted the α-NaFeO2 structure. The ferromagnetism observed below Tc=140K is attributed to the linear Ni2+(3a)–O–Mn4+(3b)–O–Ni2+(3a) magnetic paths, from which we derive that 7% of the nickel occupies the (3a) Wyckoff position in place of Li, constituting a Ni2+(3a) defect. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni2+ (S =1) and Mn4+ (S =3/2) spin-only values. Results of structural and magnetic properties of chemically delithiated sample are consistent with the electronic state Mn4+/Ni4+ and the high-spin configuration for Ni4+ ions. The LiNi0.5Mn0.5O2 electrode sintered at 900°C delivers a capacity 166mAh/g at 0.1C rate which is capacity retention of 95%. [Copyright &y& Elsevier]

Abstract: We present the magnetic properties of LiNi0.5Mn1.5O4 spinels prepared by the sol–gel and pyrolysis techniques. Structural properties show that the material synthesized by pyrolysis method exhibit an ordered spinel structure. Characterization methods include SQUID magnetometry and ESR spectroscopy. Magnetic measurements have evidenced the ferromagnetic ordering below in LiNi0.5Mn1.5O4. Results show that actually no impurity phase is detected in LiNi0.5Mn1.5O4, thus the ferrimagnetic behavior is attributed to an intrinsic property of this material. The magnetic order in this case is trivially a collinear ferrimagnetic ordering in which both the Ni sublattice and the Mn sublattice are ferromagnetic. ESR measurements show a two-component signal with a complex shape. The dominant band is assigned to Mn4+ ions that are the only paramagnetic entities in this compound. [Copyright &y& Elsevier]

This paper reports the microstructure of LiXPO4 (X=Ni, Co, Mn) materials prepared by solid state chemical reaction. The variation in microstructure of these phospho-olivines is mainly due to a difference in the XO6 cationic octahedral environment, which is discussed using a molecular vibration model to elucidate the bonding between various structural units. A direct relationship is established between the vibrational frequencies and the second ionisation potential of the metal (X) in LiXPO4. [Copyright &y& Elsevier]

The structure and magnetic properties of lithium iron pyrophosphate, i.e., Li2Fe3(P2O7)2 or LiFe1.5P2O7, synthesized using a facile metal acetate approach for application in lithium-ion batteries, are investigated in detail. The high-resolution transmission electron microscopy, selected area electron diffraction, and x-ray diffraction measurements indicate that Li2Fe3(P2O7)2 is crystallized in the monoclinic structure, without any indication of crystallographic defects such as dislocations or misfits, and exhibit smooth surface morphology. The evaluated lattice parameters are a=0.698 76 nm, b=0.812 36 nm, c=0.964 22 nm, and β=111.83° (P21/c space group). Infrared spectroscopic measurements indicate the presence of P2O7 groups, which are formed by the two PO4 tetrahedral groups connected together. The magnetic measurements indicate that Li2Fe3(P2O7)2 is a weak antiferromagnetic material with TN=20 K exhibiting a Curie constant Cp=3.38 emu K/mol per Fe ion and a negative value of the Weiss temperature (Θp=-15 K). The absence of higher valence state Fe impurities and antiferromagnetic interactions due to the greater distance between two equivalent magnetic ions, which vanishes the Fe–O–Fe superexchange interactions, is confirmed. [ABSTRACT FROM AUTHOR]

Abstract: A series of LiNi1/3Mn1/3Co1/3O2 samples with α-NaFeO2 structure belonging to the D3d 5 space group were synthesized using tartaric acid as a chelating agent by wet-chemical method. Different acid to metal-ion ratios R have been used to investigate the effect of this parameter on the physical and electrochemical properties. We have characterized the reaction mechanism, the structure, and morphology of the powders by TGA, XRD, SEM and TEM imaging, completed by magnetic measurements, Raman scattering spectroscopy, and complex impedance experiments. We find that the LiNi1/3Mn1/3Co1/3O2 sintered at 900°C for 15h with an acid to metal-ion ratio R =2 was the optimum condition for this synthesis. For this optimized sample, only 1.3% of nickel-ions occupied the 3b Wyckoff site of the lithium-ions sublattice. The electrochemical performance has been investigated using a coin-type cell containing Li metal as the anode. The electronic performance is correlated to the concentration of the Ni(3b) defects that increase the charge transfer resistance and reduce the lithium diffusion coefficient. The optimized cell delivered an initial discharge capacity of 172mAhg−1 in the cut-off voltage of 2.8–4.4V, with a coulombic efficiency of 93.4%. [ABSTRACT FROM AUTHOR]

Abstract: Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M =Ni+Mn+Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined α-NaFeO2 structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li1−y Ni y ]3b [Li x+y Ni(1−x)/3−y Mn(1−x)/3Co(1−x)/3]3a O2 (x =0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni2+-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M =1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge–discharge cycling. Data obtained with Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 reflected the high degree of sample optimization. An initial discharge capacity of 150mAhg−1 was delivered at 1C-rate in the cut-off voltage of 3.0–4.3V. More than 95% of its initial capacity was retained after 30 cycles at 1C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li1+x (Ni1/3Mn1/3Co1/3)1−x O2. [Copyright &y& Elsevier]

Abstract: A novel lithium iron phosphate has been synthesized by a solution route at moderate temperature. The structure was determined from powder by XRD, HRTEM and SAED experiments. LiFe2P3O10 tripolyphosphate crystallizes in the monoclinic system, space group P21 /m, with lattice constants a =4.597(7)Å, b =8.566(4)Å, c =9.051(4)Å, β =97.47° and Z =2. Internal and external vibrational modes (Raman and FTIR) show that the dominant spectral features come from the (P3O10)5− oxo-anions displaying internal and external modes along with the P–O–P bridging modes. Magnetic measurements are consistent with the high-spin configuration of Fe2+ cation with an effective magnetic moment 5.51μB. A weak antiferromagnetic ordering is observed below the Néel temperature at T N =19K. Electron paramagnetic resonance spectroscopy confirms this electronic configuration and provides evidence of the presence of a carbonaceous layer onto the particle surface. Electrochemical measurements were carried out in lithium cells with LiPF6–EC–DEC electrolyte at 25°C. The material delivered a capacity 70mAh/g in the voltage range 2.7–3.9V, close to the theoretical value (72mAh/g). The resulting cyclic voltammogram indicates a stable structure with a good reversibility with the redox peaks at 3.26 and 3.13V vs. Li0/Li+. [Copyright &y& Elsevier]

Abstract: A series of LiMn y Fe1−y PO4 samples have been prepared in the whole range 0≤ y ≤1. Chemical delithiation could be achieved to obtain Mn y Fe1−y PO4 in the range 0≤ y ≤0.8, keeping the same crystal phase (olivine structure, space group Pnma). The composition y =0.8 is the limit where the delithiated phase is still crystallized, but abruptly suffers strains at the molecular scale evidenced by both optical spectroscopy and X-ray diffraction. The analysis of the magnetic properties shows that in all the samples the concentration of impurities is negligible. The concentration of polarons, either holes associated to Li vacancies in LiMn y Fe1−y PO4 or electrons associated to the existence of Li left in the matrix of Mn y Fe1−y PO4, is found to be small (≤1%) in all the samples. For y ≤0.6, all the Mn3+ ions Mn y Fe1−y PO4 are in the high-spin state (S =2). At larger manganese concentration, however, the Mn3+ ions in excess of the critical concentration y c =0.6 undergo a transition to the low-spin state (S =1). As a consequence, and in contrast with prior works, we find that Mn0.8Fe0.2PO4 has magnetic interactions that are much smaller, and no antiferromagnetic ordering in this compound is detected, at least above 20K. Antiferromagnetic ordering that had been reported so far for Mn y Fe1−y PO4 at large y-composition might come from incomplete delithiation. The spin-transition of Mn3+ in concentration (y–y c) to the low-spin state is at the origin of the strain fields at the molecular scale that increase with y for y >0.6, and ultimately prevents the full delithiation for y >0.8. This result sheds light on the reason for the degradation of cathode properties in Mn-rich compounds of the heterosite–purpurite series, while the electrochemical properties are good in the range y ≤0.6 but only at slow rates, due to the very small hopping mobility of the small polaron. [Copyright &y& Elsevier]

Abstract: The effect of H2O on carbon-coated LiFePO4 particles was investigated by chemical analysis, structural analysis (X-ray diffraction, SEM, TEM), optical spectroscopy (FTIR, Raman) and magnetic measurements. Upon immersion in water, part of the product floats while the main part sinks. Both the floating and the sinking part have been analyzed. We find that the floating and sinking part only differ by the amount of carbon that partly detaches from the particles upon immersion in water. Exposure to H2O results in rapid attack, within minutes, of the surface layer of the particles, because the particles are no longer protected by carbon. The deterioration of the carbon coat is dependent on the synthesis process, either hydrothermal or solid-state reaction. In both cases, however, the carbon coat is permeable to water and fails to protect the surface of the LiFePO4 particles. The consequence is that this immersion results in the chemical attack of LiFePO4, but is restricted to the surface layer of the particles (few nanometers-thick). In case the particles are simply exposed to humid air, the carbon coat protects the particles more efficiently. In this case, the exposure to H2O mainly results in the delithiation of the surface layer, due to the hydrophilic nature of Li, and only the surface layer is affected, at least for a reasonable time of exposure to humid air (weeks). In addition, within this timescale, the surface layer can be chemically lithiated again, and the samples can be dried to remove the moisture, restoring the reversible electrochemical properties. [Copyright &y& Elsevier]

Abstract: Amorphous analogs of lithium–iron–phosphates (LFP) with olivine-like local order were prepared by standard press-quenching method and their thermal stabilities as well as structural and electric properties were studied for the first time. Glass transition temperature T g determined by DTA method is equal to 492–523 °C depending on the glass composition. Fourier transform infrared (FTIR) absorption spectroscopy was used to study local order. Local structure and thermal properties are almost independent on the lithium content. Electrical properties were studied by impedance spectroscopy. Impedance measurements indicated that the studied lithium–iron–phosphate glasses with olivine-like local order exhibit predominantly electronic (polaronic) conductivity. Total electrical conductivity at 450 °C for a glass of nominal composition LiFePO4 approaches 10−2 S/cm. Electrical conductivity at 25 °C of Li0.4FePO4 glass after nanocrystallization (caused by heating up from room temperature to the beginning of crystallization temperature) increased by a factor close to 4. Nanocrystallization seems to be the way for electrical conductivity improvement of olivine-like cathode materials. [Copyright &y& Elsevier]

We use the combination of density functional theory and dynamical mean-field theory to compute the Curie temperature of the iron body-centered cubic α phase and probe its pressure dependence. Our calculations reveal thatTCshows a decrease which is very weak over a domain of pressures that is much larger than the stability domain of the α phase. This is consistent with the experimental results. We highlight the importance of the Hund's coupling J not only on the electronic and magnetic properties but also on the structural properties. Lastly, we analyze the electronic and magnetic properties under pressure and discuss the evolution of magnetic moments in both phases in relation to the change of Curie temperature., (© 2022 IOP Publishing Ltd.)

Objective: The aim was to improve distressing patient-reported outcomes (PROs) that persisted in RA patients with clinically controlled inflammation (controlled RA)., Methods: In a pragmatic pilot study, we offered mindfulness-based stress reduction (MBSR), a group intervention, to controlled RA patients who had high (≥16) Centre for Evaluation Studies depression (CES-D) scores and/or patient general assessment of disease activity (PGA) at least 2/10 larger than evaluator general assessment (EGA) (PGA-EGA: Delta). Evaluations before, 6 and 12 months after MBSR included CES-D, PGA, modified HAQ, simple disease activity index (SDAI), anxiety (general anxiety disorder 7; GAD-7), coping strategies (coping with health injuries and problems; CHIP), sleep disturbance and pain. Facilitators and obstacles to recruitment and participation were identified. A subset of patients was interviewed for qualitative analysis of their experience., Results: Out of 306 screened patients, 65 were referred, 39 (60%) agreed and 28 (43%) completed MBSR. Anticipated burden, timing and frequency of group meetings, commuting issues, age extremes and co-morbidities were barriers to participation. Up to 12 months after MBSR, anxiety, depression, emotion-oriented coping, sleep and function significantly improved. Nonetheless, no significant impact was observed on pain, PGA, Delta or SDAI. The interviews revealed that benefits, including integration of effective coping strategies, were maintained., Conclusion: We addressed MBSR feasibility issues and selection of outcomes in controlled RA patients with distressing PROs. For patients who chose to participate in MBSR, lasting benefits were evident for anxiety, depression, sleep and function. Larger studies are required to evaluate the weaker impact of MBSR on RA-related pain and PGA., (© The Author(s) 2022. Published by Oxford University Press on behalf of the British Society for Rheumatology.)

This article reports on a historical investigation carried out on the conical object MIN000-3519 preserved in the mineralogy collections of the Muséum National d'Histoire Naturelle at Paris (France). The mineralogist René-Just Haüy (1743-1822) included this object, cut in a single pyrite (FeS 2 ) crystal, in his working collection with the references 'Sulphured iron, mirror of the Incas, of Peru, M. de Jussieu'. All of the research lines followed lead the author to Joseph de Jussieu (1704-1779) and his shipments of botanical specimens and various other samples from South America. As a member of the Godin-La Condamine-Bouguer geodesic expedition on the equator (1735-1743), he returned to France only after 36 years (1771), ill, exhausted and dispossessed of the scientific product of his Andean collections. This pyrite mirror is important because, in addition to appearing to be the only archaeological object that can be linked to Joseph's peregrinations in America, it resembles other specimens found at sites of the Cañaris culture (500-1500 AD) in Ecuador. Preserved within the de Jussieu family, this object would presumably have been given to Haüy by Joseph's heirs, his nephews Antoine-Laurent (1748-1836) or Laurent-Pierre (1792-1866), with whom he had close ties.

Electric field gradient (EFG) tensors in the equatorial plane of the linear UO 2 2+ ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn-Sham methods with and without environment embedding for Cs 2 UO 2 Cl 4 and Cs 2 UO 2 Br 4 . This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U-O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U-X bond (X = Cl, Br), and the second is parallel to the UO 2 2+ ion; in Cs 2 UO 2 Cl 4 , the components are nearly equal in magnitude, whereas in Cs 2 UO 2 Br 4 , due to short-range bromide-cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair. The directions and relative magnitudes of the field gradient principal axes are found to be sensitive to the σ and π electron donation by the ligands and the model of the environment. Chlorine-35 NQR spectra of 235 U-depleted and 235 U-enriched Cs 2 UO 2 Cl 4 exhibited no uranium-isotope-dependent shift, but the resonance of the depleted sample displayed a 58% broader line width.

The electronic structure and circular dichroism spectra of the ytterbium(III) complex [Yb(DOTMA)] - are calculated using complete and restricted active space self-consistent field wavefunction methods with the spin-orbit coupling treated by the state interaction approach. The influence of the dynamical correlation effect is then included via the 2nd order perturbation method. The experimental circular dichroism spectrum is well reproduced by calculations, both in terms of relative energy excitations and in terms of rotatory strength intensities. The results allow highlighting the mechanism that drives the chiroptical properties in Yb(III) complexes and reveal the importance of taking into account the 4f 12 5d 1 electronic configurations in the calculated wavefunctions to properly describe the chiroptical properties of the 4f-4f transitions.

The synthesis, structural and photophysical characterization, and theoretical studies on homo/heteroleptic neutral 2D-layered coordination polymers (CPs), obtained by combining the Er III ion with chlorocyananilate (ClCNAn) and/or tetrafluoroterephthalate (F 4 BDC) linkers, are herein reported. The structure of the heteroleptic Er III -based CP, formulated as [Er 2 (ClCNAn) 2 (F 4 BDC)(DMSO) 6 ] n ( 1 ) is also reported. 1 crystallizes in the triclinic P 1̅ space group, and the structure consists of neutral 2D layers formed by Er III ions linked through the two linkers oriented in such a way that the neighboring 2D layers are eclipsed along the a axis, leading to parallelogram-like cavities. Photophysical measurements highlight the prominent role of chlorocyananilate linkers as optical antennas toward lanthanide ions, while wave-function-theory analysis supports the experimental findings, providing evidence for the effect of ligand substitution on the luminescence properties of homo/heteroleptic 2D CPs.

Sandwich complexes of lanthanides have recently attracted a considerable amount of interest due to their applications as Single Molecule Magnet (SMM). Herein, a comprehensive series of heteroleptic lanthanide sandwich complexes ligated by the cyclononatetraenyl (Cnt) and the cyclooctatetraenyl (Cot) ligand [Ln(Cot)(Cnt)] (Ln=Tb, Dy, Er, Ho, Yb, and Lu) is reported. The coordination behavior of the Cnt ligand has been investigated along the series and shows different coordination patterns in the solid-state depending on the size of the corresponding lanthanide ion without altering its overall anisotropy. Besides the characterization in the solid state by single-crystal X-ray diffraction and in solution by 1 H NMR, static magnetic studies and ab initio computational studies were performed., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)