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We report the structural, magnetic, electrical and magentoresistance properties of (La 0.75 Ca 0.15 Sr 0.1 MnO 3 ) 1− x (YBa 2 Cu 3 O 7−δ ) x (with x =0, 0.025, 0.05, 0.075, 0.1, 0.2, and 0.3) composites synthesized through sol–gel method. The powder X-ray diffraction patterns indicate no evidence of reaction between La 0.75 Ca 0.15 Sr 0.1 MnO 3 (LCSMO) and YBa 2 Cu 3 O 7−δ (YBCO). The addition of YBCO induces a reduction of the total magnetization while the Curie temperature remains almost constant (∼312 K). The behavior of the electrical resistivity evolves differently depending on the doping level. Above the paramagnetic–insulating transition temperature the resistivity data were best-fitted by using the adiabatic small polaron and variable range hopping models. Ferromagnetic–metallic regime in the composites seems to emanate from the electron–phonon or/and electron–magnon scattering processes. With increasing the YBCO doping content (until x =0.1), the positive magnetoresistance (MR) of YBCO phase dominates the negative MR of LCSMO one, which gives rise to the decreasing of MR of the composites.

International audience; Under-doped La-214 cuprates show a charge-and spin-modulation known as " stripes " [1]. These stripe modulations are (quasi)-static close to 1/8 hole doping where superconductivity is suppressed. The pseudo-gap phase of other cuprate compounds recently also revealed charge modulation, but interpreted rather as a charge density wave (CDW) [2, 3, 4], that possibly competes with superconductivity. In this context, to better understand the interplay between the stripe phase and the superconductivity, we use angle-resolved photoemission spectroscopy to study the electronic band structure and gap in La-214 cuprates near 1/8 doping (La 2−x−y Nd y Sr x CuO 4 (x = 0.12; y = 0.0 & 0.4)) and compare with the previous results in the same system [5] and La 1.86 Ba 0.14 CuO 4 [6]. Our data shows a loss of spectral intensity towards the end of the Fermi arcs, that is possibly due to a strong renormalisation, as already pointed out elsewhere * matteo.dastuto@neel.cnrs.fr-Institut Néel CNRS-25, av des Martyrs-38042 Grenoble cedex 9; tel: (+33)(0)4 76 88 12 84 [5], with a noisy but still measurable gap. On the nodal direction no gap is observed within our statistics, but a sizeable decrease in intensity with temperature. Moreover, we do not see any shadow band, but our Fermi surface can be well modelled with a single electron band calculation in the tight binding approximation, even very close to the 1/8 doping La 2−x−y Nd y Sr x CuO 4 with and without Nd substitution.

International audience; A new crystal growth device, in which a high static external electric voltage (up to 14 kV) is added to a floating zone method, is described. Our first experiments show that the application of such an electric field acts like an external force, introducing a pressure effect which is in direct competition with temperature in the solid/liquid thermodynamic equilibrium. High electric fields could therefore be an additional parameter in crystal growth, opening original routes to the synthesis of new materials.

The low energy magnetic excitations spectra of the pristine and doped quasi-one-dimensional spin chains cuprates $\mathrm{SrCu}{\mathrm{O}}_{2}$ have been investigated by inelastic neutron scattering. The momentum-integrated magnetic dynamical structure factor yields a constant integrated intensity with regard to energy in the pure compound, while it shows a strong decay, at low energies, in the compounds doped with nonmagnetic impurities, namely, $\mathrm{SrC}{\mathrm{u}}_{0.99}{\mathrm{M}}_{0.01}{\mathrm{O}}_{2}$ (with $M=\mathrm{Zn}$ or Mg) and $\mathrm{S}{\mathrm{r}}_{0.99}\mathrm{L}{\mathrm{a}}_{0.01}\mathrm{Cu}{\mathrm{O}}_{2}$ ($\mathrm{C}{\mathrm{u}}^{+}$ carrying $S=0$ created within the chains). These results evidence the opening of a spin pseudogap in the two-spinon continuum of $\mathrm{SrCu}{\mathrm{O}}_{2}$ upon doping, stemming from disruptions of the spin chains by quantum impurities.

The three polyoxotungstates [(NaOH2)2CoII2(As2W15O56)2]18– (1), [(NaOH2)(CoIIOH2)CoII2(As2W15O56)2]17– (2), and [(CoIIOH2)2CoII2(As2W15O56)2]16– (3) have been prepared in aqueous solution upon mixing cobalt(II) salts with the ligand [As2W15O56]12–. The reaction of 1 or 2 with the Fe3+ ion leads invariably to the same species [(FeIIIOH2)(CoIIOH2)CoII2(As2W15O56)2]15– (4) possessing three cobalt atoms and a single iron atom. However, if the Fe-containing homologue of compound 1, that is, the polyoxotungstate [(NaOH2)2FeIII2(As2W15O56)2]16– (5), is employed instead to react with the Co2+ ion, the species [(CoIIOH2)2FeIII2(As2W15O56)2]14– (6) is obtained, having two cobalt atoms and two iron atoms. The compounds 1, 2, 3, 4, and 6 are described for the first time and have been characterized by several physicochemical methods such as FTIR, UV–visible, ATG, and elemental analysis. Structural analysis by single-crystal X-ray diffraction has been carried out with compounds 2 (monoclinic space group P21/c, a = 17.0...

Magnetite synthesized via three different synthesis routes (coprecipitation process in aqueous media, electrochemical synthesis in presence of complexing agents and solid state reaction at high temperature) has been characterized by X-Ray diffraction, scanning electron microscopy, thermal analysis (TGA), FT-IR and Mossbauer spectroscopies. Although each procedure gave homogeneous magnetite powders, many differences could be seen in the physico-chemical properties of the samples mostly depending on the synthesis conditions. For instance, at least two factors seem to have a huge impact onto the Fe3O4 behaviour: the presence of hydration water molecules and the particle size of the powders since a superparamagnetic behaviour was observed with the thinnest particles, at room temperature, on the Mossbauer spectra via the appearance of line broadening and a pronounced central doublet.

The structural characterization and electrochemical performance of three nanosized iron oxyhydroxides (β-FeOOH, γ-FeOOH and δ-FeOOH) are reported in this work. The interest of having small particle sizes is to be able to circumvent the low intrinsic ionic conductivity of these materials through the increase of the active volume proportion of the operating grain, during the insertion process. Low temperature synthesis routes, in aqueous media, were thus used to obtain such crystallites with nanometer dimensions. The theoretical specific capacity of these materials is as high as 300 mA h g −1 which is actually very interesting for lithium batteries applications. However, the electrochemical behaviour greatly depends on the structure of the compounds. A phase transformation was, for example, evidenced in the case of γ-FeOOH first lithiation whereas the best performance were obtained with β-FeOOH, which develops a stable capacity of 180 mA h g −1 , after 10 cycles, at C/10.

The three novel, multi-nickel-substituted heteropolytungstates [Ni6As3W24O94(H2O)2]17- (1), [Ni3Na(H2O)2(AsW9O34)2]11- (2), and [Ni4Mn2P3W24O94(H2O)2]17- (3) have been synthesized and characterized by IR, elemental analysis, electrochemistry, and magnetic studies. Single-crystal X-ray analysis was carried out on Na16.5Ni0.25[Ni6As3W24O94(H2O)2]·54H2O, which crystallizes in the triclinic system, space group P1, with a = 17.450(4) A, b = 17.476(4) A, c = 22.232(4) A, α = 85.73(3)°, β = 89.74(3)°, γ = 84.33(3)°, and Z = 2, Na11[Ni3Na(H2O)2(AsW9O34)2]·30.5H2O, which crystallizes in the triclinic system, space group P1, with a = 12.228(2) A, b = 16.743(3) A, c = 23.342(5) A, α = 78.50(3)°, β = 80.69(3)°, γ = 78.66(3)°, and Z = 2, and Na17[Ni4Mn2P3W24O94(H2O)2]·50.5H2O, which crystallizes in the monoclinic system, space group P21/c, with a = 17.540(4) A, b = 22.303(5) A, c = 35.067(7) A, β = 95.87(3) A, and Z = 4. Polyanion 1 consists of two B-α-(Ni3AsW9O40) Keggin moieties linked via a unique AsW6O16 fragmen...

Fault-filling calcite crystals sampled from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been studied in order to test the potentiality of calcite (U-Th)/He dating, based on recognized He retention behavior in crystal lattice at surface temperature (Copeland et al., 2007). The samples have been selected because of their relatively old Eocene to Oligocene precipitation age and cold thermal history (

We combine a wide variety of experimental techniques to analyze two heretofore mysterious phase transitions in multiferroic bismuth ferrite at low temperature. Raman spectroscopy, resonant ultrasound spectroscopy, EPR, X-ray lattice constant measurements, conductivity and dielectric response, specific heat and pyroelectric data have been collected for two different types of samples: single crystals and, in order to maximize surface/volume ratio to enhance surface phase transition effects, BiFeO3 nanotubes were also studied. The transition at T=140.3K is shown to be a surface phase transition, with an associated sharp change in lattice parameter and charge density at the surface. Meanwhile, the 201K anomaly appears to signal the onset of glassy behaviour., submitted to PRB

We report a direct observation of a sharp Kohn-type anomaly in the doubly degenerate copper-oxygen bond-stretching phonon mode occurring at $\mathbf{q}=(0.3,0,0)$ in ${\text{La}}_{2\ensuremath{-}x}{\text{Ba}}_{x}{\text{CuO}}_{4+\ensuremath{\delta}}$, with $x=0.14\ifmmode\pm\else\textpm\fi{}0.01$, thanks to the high $\mathbf{Q}$ resolution of inelastic x-ray scattering. This anomaly is clearly seen when the inelastic signal is analyzed using a single mode but is also consistent with a two-mode hypothesis, possibly due to a splitting of the degenerate modes due to symmetry-breaking stripes. Our observation shows that the effect persists at the stripe-propagation vector in a superconducting system close to optimal doping.

The recent discovery of spin ice is a spectacular example of the noncoplanar spin arrangements that can arise in the pyrochlore ${A}_{2}{B}_{2}{\mathrm{O}}_{7}$ structure. We present magnetic and thermodynamic studies on the metallic ferromagnet pyrochlore ${\mathrm{Sm}}_{2}{\mathrm{Mo}}_{2}{\mathrm{O}}_{7}$. Our studies, carried out on oriented crystals, suggest that the Sm spins have an ordered spin-ice ground state below about ${T}^{*}=15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature and field evolution of the ordered spin-ice state are governed by an antiferromagnetic coupling between the Sm and Mo spins. We propose that as a consequence of a robust feature of this coupling, the tetrahedra aligned with the external field adopt a one-in, three-out spin structure as opposed to the three-in, one-out structure in dipolar spin ices, as the field exceeds a critical value.

A tetranuclear manganous Wells–Dawson sandwich-type polyoxometalate has been synthesized by the reaction of α-Na12(As2W15O56) with an aqueous solution of MnCl2·4H2O. The structure of this complex, αββα-Na16(MnIIOH2)2MnII2(As2W15O56)2·55H2O (Na1), was determined by single-crystal X-ray crystallography (a = 14.5230(12) A, b = 14.7104(13) A, c = 19.8927(17) A, α = 84.326(2)°, β = 81.709(2)°, γ = 65.584(2)°, triclinic, R1 = 6.2%, based on 26721 independent reflections) and is similar to the phosphorus analogue, αββα-Na16(MnIIOH2)2MnII2(P2W15O56)2 (Na2). Magnetization studies confirm that both Na1 and Na2 show antiferromagnetic coupling of the four Mn(II) centers. Despite the structural similarities, electrochemical studies reveal that the presence of arsenic shifts the Mn waves to more positive potentials. Catalytic studies confirm that 1 is a significantly better catalyst than 2 for the H2O2-based epoxidation of cis-cyclooctene, cyclohexene, and 1-hexene.

The novel nickel-substituted, dimeric phosphotungstate [Ni(3)Na(H(2)O)(2)(PW(9)O(34))(2)](11-) (1) has been synthesized and characterized by IR spectroscopy, elemental analysis, and electrochemistry. X-ray single-crystal analysis was carried out on Na(11)[Ni(3)Na(H(2)O)(2)(PW(9)O(34))(2)].21.25H(2)O, which crystallizes in the triclinic system, space group P1, with a = 12.2467(6) A, b = 16.6031(7) A, c = 22.4017(12) A, alpha = 73.9870(10) degrees, beta = 87.6060(10) degrees, gamma = 79.344(2) degrees, and Z = 2. The polyanion consists of two lacunary B-alpha-[PW(9)O(34)](9-) Keggin moieties linked via three nickel(II) centers and a sodium ion. The structure of 1 is composed of two fused Keggin fragments that represent different Baker-Figgis isomers (alpha- vs beta-type). Electrochemical studies show that 1 exhibits a stable and reproducible voltammetric pattern, with a first wave featuring a chemically reversible four-electron/four-proton process. An investigation of the magnetic properties indicates that the three nickel centers exhibit ferromagnetic exchange interaction.

A levitation device associated with laser heating has been developed in order to measure the structure of ceramics at very high temperature by using synchrotron radiation sources. Combined X-ray diffraction and X-ray absorption measurements have been performed on spherical solid and liquid samples in a controlled atmosphere up to 2800°C. The analysis chamber was integrated with the 7-circles goniometer of the D2AM station at the ESRF. This technique presents a novel opportunity to probe the short-range and long-range properties of high-temperature oxides up to the liquid phase. By studying the local structure around cations in oxides, we have shown that the combined XAFS and XRD data, deriving from in-situ synchrotron radiation experiments, contain valuable information on phase transitions, contributing to the optimisation of the fabrication of ceramics.

A new high temperature chamber using aerodynamic levitation and laser heating has been used to study spheres of oxide materials at temperatures up to 2100°C. Near edge studies of Fe3O4 (MP : 1597°C) and FeO (MP 1377°C) have been performed by fluorescent XANES and in situ X-ray Diffraction (XRD). Both iron oxides reveal a shift in the Fe K-absorption edge on melting to lower energies by between 2 and 3 eV. This is accompanied by an increase in the threshold resonance. Experiments with neutral and oxidising levitating gases show the same behaviour and suggest a physical origin. A possible explanation is an increase in the Fe-O bond length with a consequent reduction in physical density on melting. This would naturally result in a narrower energy gap which would lead to the observed shift in the absorption threshold to lower energies in passing from the solid to the liquid state. This would also account for the rise in the threshold resonance on melting. By performing high temperature XRD, the thermal expansion coefficients α of Al2O3 (MP 2054°C) have been obtained crystallographically by measuring the increase of the unit cell parameters. XRD curves have been recorded at several temperatures from 800°C up to the melting point. The measured coefficients are in agreement with literature data. On the technical side, some problems relating to the levitation state and temperature measurements are discussed indicating the need for improvement of the chamber.