Anisotropic susceptibility of the geometrically frustrated spin-chain compound Ca3Co2O6

Ca3Co2O6 is a system exhibiting a series of fascinating properties, including magnetization plateaus and remarkably slow dynamics at low-T. These properties are intimately related to the geometrical frustration, which results from a particular combination of features: (i) the chains are arranged on a triangular lattice; (ii) there is a large uniaxial anisotropy; (iii) the intrachain and interchain couplings are ferromagnetic and antiferromagnetic, respectively. The uniaxial anisotropy is thus an issue of crucial importance for the analysis of the physical properties of Ca3Co2O6. However, it turns out that no precise investigation of this magnetic anisotropy has been performed so far. On the basis of susceptibility data directly recorded on single crystals, the present study reports on quantitative information about the anisotropy of Ca3Co2O6.Comment: 10 pages, 5 figure

Qualitative and Semiquantitative Assessment of Exposure to Engineered Nanomaterials within the French EpiNano Program: Inter- and Intramethod Reliability Study

The relatively recent development of industries working with nanomaterials has created challenges for exposure assessment. In this article, we propose a relatively simple approach to assessing nanomaterial exposures for the purposes of epidemiological studies of workers in these industries. This method consists of an onsite industrial hygiene visit of facilities carried out individually and a description of workstations where nano-objects and their agglomerates and aggregates (NOAA) are present using a standardized tool, the Onsite technical logbook. To assess its reliability, we implemented this approach for assessing exposure to NOAA in workplaces at seven workstations which synthesize and functionalize carbon nanotubes. The prediction of exposure to NOAA using this method exhibited substantial agreement with that of the reference method, the latter being based on an onsite group visit, an expert’s report and exposure measurements (Cohen kappa = 0.70, sensitivity = 0.88, specificity = 0.92). Intramethod comparison of results for exposure prediction showed moderate agreement between the three evaluators (two program team evaluators and one external evaluator) (weighted Fleiss kappa = 0.60, P = 0.003). Interevaluator reliability of the semiquantitative exposure characterization results was excellent between the two evaluators from the program team (Spearman rho = 0.93, P = 0.03) and fair when these two evaluators’ results were compared with the external evaluator’s results. The project was undertaken within the framework of the French epidemiological surveillance program EpiNano. This study allowed a first reliability assessment of the EpiNano method. However, to further validate this method a comparison with robust quantitative exposure measurement data is necessary

Atomic layer fluorination of 5 V class positive electrode material LiCoPO4 for enhanced electrochemical performance

EJK would like to thank the Alistore ERI for the award of a studentship. The authors thank EPSRC Capital for Great Technologies Grant EP/L017008/1. The authors want to thank the French Research Network on the Electrochemical Energy Storage (RS2E) for YCB’s PhD grant. MD and NL are indebted to the IR-RMN-THC FR3050 CNRS for the spectrometer time access and the financial support of the NMR experiments.The surface fluorination of lithium cobalt phosphate (LiCoPO4, LCP) using a one‐step, room temperature processable, easily up‐scalable and dry surface modification method with XeF2 as fluorine source was developed. After fluorination, fluorine‐rich nanoparticles were observed mainly on the particle surface, which facilitates the improvement of surface stability and electrochemical performance such as cycling stability and rate capability, as the fluorinated LCP can be protected against side reactions with electrolyte or by‐products of electrolyte decomposition at high voltage (5 V). More importantly, the direct surface fluorination proved more efficient than adding a fluorinated electrolyte additive (i. e., FEC). These results suggest that surface fluorination using XeF2 is of great promise for practical applications of high voltage positive materials for lithium‐ion batteries.PostprintPeer reviewe

Oxydes de cobalt à structures dérivées de la pérovskite (états de spin et propriétés physiques)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Sign change of the thermoelectric power in LaCoO3

International audienceThe substitution of 1%-Ce4+ for La3+ in LaCoO 3 is found to change the sign of the Seebeck coefficient at room temperature. This demonstrates that not only holes but also electrons can be created in LaCoO3. The result is compatible with the Heikes formula for doping levels close to the "pure" trivalent Co3+ state. Nonetheless, the physical properties such as magnetic susceptibility, magnetization, thermal conductivity and resistivity are found to be asymmetric for hole and electron-doped LaCoO3. Such a different behaviour is ascribed to the very different spin-states of Co4+(low-spin, t 2g 5eg 0) and Co2+ (high-spin, tg 5 g 2)

Diluted magnetic interactions in an oxygen-deficient perovskite cobaltite: Magnetoresistance in the series SrCo 1-xSc xO 3-δ (0

International audienceA series of the oxygen-deficient perovskite SrCo 1- xSc xO 3-δ has been successfully prepared by using close ampoules for compositions in the range 0.05≤x≤0.5. The unit cell expansion with x is ascribed to the larger Sc 3+ ionic radius than those of the Co 3+/Co 4+ cations. At 300 K, resistivity (ρ) values of about ∼10 -2 Ω cm are measured for both x=0.05 and 0.10, but for larger x values ρ increases, reaching ρ 300 K=10 2 Ω cm for x=0.5. For the former, the lower resistivity values result from their weak ferromagnetic behavior characterized by a Curie temperature T C of ∼60 K. Interestingly, these oxides exhibit similar negative magnetoresistance values, reaching 12% in 7 T at 5 K, to those reported for the SrFe 1-xCo xO 3-δ samples. It is concluded that the simultaneous presence of non-magnetic (3d0) Sc 3+ species, substituted for cobalt, and of oxygen vacancies induce magnetic disordering, exemplified by the spin-glass like behavior of SrCo 0.5Sc 0.5O 3-δ, which favors the existence of magnetoresistance. T dependence of the ac-magnetic susceptibility (χ′) for oxygen pressure annealed SrCo 1-xSc xO 3-δ samples showing the effect of magnetic dilution induced by Sc 3+. © 2004 Elsevier Inc. All rights reserved

Magnetic quantum tunneling in Ca3Co2O6 studied by ac susceptibility: Temperature and magnetic-field dependence of the spin-relaxation time

International audienceThe geometrically frustrated spin-chain compound Ca3Co 2O6 was recently found to exhibit properties suggesting the phenomenon of quantum tunneling of the magnetization (QTM). The present paper addresses this issue by investigating the temperature and magnetic-field dependence of the characteristic spin-relaxation time τ. This study is based on the analysis of the out-of-phase ac magnetic susceptibility of single crystals. The overall behavior is found to support the occurrence of QTM in Ca3Co2O6: (i) saturation of τ at low T; (ii) observation of identical τ values in the magnetic fields corresponding to the steps in the M vs H curve at low T; (iii) existence of a dip centered at zero field in the τ vs H curve at low T. These QTM-like features found in Ca3Co2O6 are compared to those previously reported in other materials such as single-molecular magnets

Diluted magnetic interactions in an oxygen-deficient perovskite cobaltite: Magnetoresistance in the series SrCo 1-xSc xO 3-δ (0

International audienceA series of the oxygen-deficient perovskite SrCo 1- xSc xO 3-δ has been successfully prepared by using close ampoules for compositions in the range 0.05≤x≤0.5. The unit cell expansion with x is ascribed to the larger Sc 3+ ionic radius than those of the Co 3+/Co 4+ cations. At 300 K, resistivity (ρ) values of about ∼10 -2 Ω cm are measured for both x=0.05 and 0.10, but for larger x values ρ increases, reaching ρ 300 K=10 2 Ω cm for x=0.5. For the former, the lower resistivity values result from their weak ferromagnetic behavior characterized by a Curie temperature T C of ∼60 K. Interestingly, these oxides exhibit similar negative magnetoresistance values, reaching 12% in 7 T at 5 K, to those reported for the SrFe 1-xCo xO 3-δ samples. It is concluded that the simultaneous presence of non-magnetic (3d0) Sc 3+ species, substituted for cobalt, and of oxygen vacancies induce magnetic disordering, exemplified by the spin-glass like behavior of SrCo 0.5Sc 0.5O 3-δ, which favors the existence of magnetoresistance. T dependence of the ac-magnetic susceptibility (χ′) for oxygen pressure annealed SrCo 1-xSc xO 3-δ samples showing the effect of magnetic dilution induced by Sc 3+. © 2004 Elsevier Inc. All rights reserved

One dimensional compounds with large thermoelectric power: Ca 3Co2O6 and Ca3CoMO6 with M = Ir4+ and Rh4+

International audienceIn the Ca-Co-O system, there exists at least two identified phases, Ca 3Co4O9 and Ca3Co2O 6 exhibiting 2D CoO2 planes and 1D Co-Co chains, respectively. Both oxides are characterized by large thermopower values at room temperature, the largest value being obtained for Ca3Co 2O6 (Seebeck coefficient, S300 K = 450 μV K-1). However, the electrical resistivity of the latter is too large (typically 50 Ω cm) for applications as thermopower materials. Interestingly, the substitutions of Ir4+ or Rh4+ for one cobalt out of two in the chain do not greatly affect the electronic properties in contrast to the substitution by Sc3+ (3d0). This emphasizes that the Ir or Rh cations can play a similar role to that of the Co cations. This opens a new route for the search of new thermoelectric materials alternative to the cobaltites. © 2003 Elsevier B.V. All rights reserved