Large magnetoresistances and non-Ohmic conductivity in EuWO[1+x]N[2-x]

The magnetic field and voltage dependent electronic transport properties of EuWO[1+x]N[2-x] ceramics are reported. Large negative magnetoresistances are observed at low temperatures, up to 70% in the least doped (x=0.09) material. Non-Ohmic conduction emerges below the 12 K Curie transition. This is attributed to a microstructure of ferromagnetic conducting and antiferromagnetic insulating regions resulting from small spatial fluctuations in the chemical doping

Síntesis, estructura y propiedades de transporte de nuevos óxidos complejos de cobre, plata y plomo

A solid solution of formula Ag5Pb2-xCuxO6, (x = 0, 0.1, 0.3, 0.5) is reported. The synthesis was carried out by coprecipitation of Ag(I), Pb(II) and Cu(II) nitrates in alkaline media. The structure of the series is that of the parent Ag5Pb2O6, with Cu(II) occupying part of the octahedral Pb(IV) sites. This substitution induces interesting changes in the transport properties of the different members of the series, which range from metallic conductivity to semiconducting behavior. From Rietveld analysis for Ag5Pb1.5Cu0.5O6, the best fit is obtained for a model with Pb and Cu disordered occupying the octahedral site (Pm1, a = 5.8306(9) Å, c = 6.3430(6) Å, V = 187.37 Å3).<br><br>Se presenta la síntesis y caracterización de la serie de disolución sólida Ag5Pb2-xCuxO6, (x = 0, 0.1, 0.3, 0.5). La síntesis se llevó a cabo mediante coprecipitación de los nitratos de Ag(I), Pb(II) y Cu(II) en medio básico. La estructura de la serie es la del óxido Ag5Pb2O6, con el Cu(II) ocupando parcialmente los sitios octaédricos del Pb(IV). Esta sustitución induce cambios interesantes en las propiedades de transporte eléctrico de los miembros de la serie, que van desde conductividad metálica a comportamiento semiconductor. El análisis Rietveld para el óxido Ag5Pb1.5Cu0.5O6, mostró un modelo estructural óptimo en el que Pb y Cu comparten el sitio octaédrico en una distribución desordenada (Pm1, a = 5.8306(9) Å, c = 6.3430(6) Å, V = 187.37 Å3)

ChemInform Abstract: Electronic Tuning of Two Metals and Colossal Magnetoresistances in EuWO1+xN2-x Perovskites.

This article is closed access.A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN 2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN 2-x perovskites that show a wide range of compositions -0.16 < x < 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x < 0 regime corresponds to oxidation of Eu (hole doping of the Eu:4f band), whereas x > 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified. © 2010 American Chemical Society

Electronic tuning of two metals and colossal magnetoresistances in EuWO1+ xN2- x perovskites

A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN 2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN 2-x perovskites that show a wide range of compositions -0.16 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified. © 2010 American Chemical Society

Nanoporous polymeric templates systems for the confined growth of epitaxial ferromagnetic complex oxides nanostructures.

9-13 March 2015International audienceSelective synthesis for integrated nanomaterials with controllable morphology and composition represents an emerging research area in nanoscience and nanotechnology because the intrinsic properties behind nanostructures are generally phase-, shape-, and size- dependent. In this direction the present work shows the capabilities of nanoporous polymeric template systems directly supported on different substrates for the confined growth of epitaxial ferromagnetic complex oxides nanostructures (see figure1). In particular, we describe the versatility and potentiality of sol-gel precursor solutions combined with track-etched polymers to synthesize i) vertical polycrystalline La0.7Sr0.3MnO3 nanorods on top of single crystal perovskites [1,2], ii) single crystalline manganese based octahedral molecular sieves (OMS) nanowires on silicon substrates [3-5], and iii) the epitaxial directional growth of single crystal OMS nanowires when grown on top of fluorite-type substrates [6]. The influence of the distinct growth parameters on the nanostructural evolution of the resulting nanostructures and their magnetic properties are studied in detail. Therefore, we demonstrate that the combination of soft-chemistry and epitaxial growth opens new opportunities for the effective integration of novel technological functional complex oxides nanomaterials on different substrates. [1] A. Carretero-Genevrier et al. Chem.Soc.Rev., 43, 2042-2054 (2014) [2] A. Carretero-Genevrier et al. Adv.Funct.Mater., 20, 892-897. (2010). [3] A. Carretero-Genevrier et al. Chem.Mater., 26 (2), 1019–1028 (2014) [4] A. Carretero-Genevrier et al. JACS., 133 (11), 4053–4061 (2011) [5] J. Gazquez et al. M&M., 20 (03) 760-766 (2014) [6] A. Carretero-Genevrier et al. Chem.Comm., 48, 6223-6225 (2012

Chemical solution growth of La0.7Sr0.3MnO3 nanotubes in confined geometries

International audienceSelf-standing La0.7Sr0.3MnO3 nanotubes with outer diameter ranging from 100 - 200 nm have been successfully synthesized by template assisted chemical solution deposition using nanoporous anodized alumina membranes of varying pore size. This template synthetic strategy provides rather monodisperse size distributed nanotubes. A sol-gel based polymer precursor route was used to fill the porous membranes and a subsequent heat treatment (700-1000ºC) enabled the phase formation and crystallization of the nanotubes. A good control over viscosity, stoichiometry and stability of the precursor solution were identified as crucial parameters for the template aided synthesis. The synthesized La0.7Sr0.3MnO3 nanotubes are polycrystalline and ferromagnetic with a Curie temperature of 350 K. Control over the nanowall thickness is attained by varying template filling time which is corroborated by magnetic moment results

Nanoporous polymeric templates systems for the confined growth of epitaxial ferromagnetic complex oxides nanostructures.

9-13 March 2015International audienceSelective synthesis for integrated nanomaterials with controllable morphology and composition represents an emerging research area in nanoscience and nanotechnology because the intrinsic properties behind nanostructures are generally phase-, shape-, and size- dependent. In this direction the present work shows the capabilities of nanoporous polymeric template systems directly supported on different substrates for the confined growth of epitaxial ferromagnetic complex oxides nanostructures (see figure1). In particular, we describe the versatility and potentiality of sol-gel precursor solutions combined with track-etched polymers to synthesize i) vertical polycrystalline La0.7Sr0.3MnO3 nanorods on top of single crystal perovskites [1,2], ii) single crystalline manganese based octahedral molecular sieves (OMS) nanowires on silicon substrates [3-5], and iii) the epitaxial directional growth of single crystal OMS nanowires when grown on top of fluorite-type substrates [6]. The influence of the distinct growth parameters on the nanostructural evolution of the resulting nanostructures and their magnetic properties are studied in detail. Therefore, we demonstrate that the combination of soft-chemistry and epitaxial growth opens new opportunities for the effective integration of novel technological functional complex oxides nanomaterials on different substrates. [1] A. Carretero-Genevrier et al. Chem.Soc.Rev., 43, 2042-2054 (2014) [2] A. Carretero-Genevrier et al. Adv.Funct.Mater., 20, 892-897. (2010). [3] A. Carretero-Genevrier et al. Chem.Mater., 26 (2), 1019–1028 (2014) [4] A. Carretero-Genevrier et al. JACS., 133 (11), 4053–4061 (2011) [5] J. Gazquez et al. M&M., 20 (03) 760-766 (2014) [6] A. Carretero-Genevrier et al. Chem.Comm., 48, 6223-6225 (2012

Confined Sol-Gel route to epitaxial Octahedral Molecular Sieve nanowires on silicon

26-30 Mai 2014International audienceManganese oxides octahedral molecular sieves (OMS) with mixed-valence frameworks have been widely used as bulk material in catalysis, semiconductor industry, and batteries. Monolithic direct integration of OMS with vertically oriented crystals on a semiconductor platform is challenging due to difficulties on preserving epitaxy, crystalline phase, and composition. Here, we developed a new strategy to produce vertical epitaxial single crystalline OMS nanowires with tunable composition and enhanced ferromagnetic properties on Si substrates by using a chemical solution deposition approach [1]. The nanowire growth mechanism involves the use of track-etched nanoporous polymer templates combined with the controlled growth of α-quartz thin films at the Si surface, which allowed OMS nanowires to stabilize and crystallize. α-quartz layers were obtained by thermally activated devitrification of the native amorphous silica surface layer assisted by a heterogeneous catalysis driven by alkaline earth cations (Sr2+, Ba2+ or Ca2+) present in the precursor solution [2]. Therefore, the combination of soft-chemistry and epitaxial growth opens new opportunities for the effective integration of novel technological functional tunneled complex oxides nanomaterials on Si substrates [3]. [1] A. Carretero-Genevrier et al. Chem.Soc.Rev. 10.1039/C3CS60288E (2013) [2] A. Carretero-Genevrier et al. Science 340, 827 (2013) [3] A. Carretero-Genevrier et al. Chem.Mater. 10.1021/cm403064u (2013

Heteroepitaxial devitrification of silica to integrate functional oxide nanostructures on silicon

26-30 Mai 2014International audienceThe integration of quartz on silicon in thin film form is a challenging issue due to the differences in the crystal structures of these materials. In this regard, this work overcomes the main challenges for the integration of novel functional oxide materials on silicon including (i) epitaxial piezoelectric α-quartz thin films [1] and (ii) 1D single crystalline phases of manganese oxides that share common growth mechanisms [2,3]. The aim of this contribution is to discuss in detail the non classical nucleation and crystallization mechanisms of these materials grown from chemical solutions. Quartz films are crystallized by a confined devitrification of amorphous silica films assisted by a heterogeneous catalysis driven by alkaline earth cations present in the precursor solution. The films are made of perfectly oriented individual crystallites epitaxially grown on (100)-Si. The active influence of the Si substrate mediates the preferential orientation of crystal nuclei, yielding competitive growth and producing a columnar microstructure. Quartz films are piezoelectric and can be used as template for the epitaxial growth of manganese oxide nanowires on silicon. This methodology exhibits a great potential for the design of novel oxide compounds on silicon with unique properties. [1]A. Carretero-Genevrier et al. Science 340, 827 (2013) [2]A. Carretero-Genevrier et al. Chem.Mater. 10.1021/cm403064u (2013) [3]A. Carretero-Genevrier et al. Chem.Soc.Rev. 10.1039/C3CS60288E (2013