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Azough F.,University of Manchester | Freer R.,University of Manchester | Yeandel S.R.,University of Bath | Baran J.D.,University of Bath | And 20 more authors.
Journal of Electronic Materials | Year: 2015

Semiconducting Ba6−3xNd8+2xTi18O54 ceramics (with x = 0.00 to 0.85) were synthesized by the mixed oxide route followed by annealing in a reducing atmosphere; their high-temperature thermoelectric properties have been investigated. In conjunction with the experimental observations, atomistic simulations have been performed to investigate the anisotropic behavior of the lattice thermal conductivity. The ceramics show promising n-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical conductivity, and temperature-stable, low thermal conductivity; For example, the composition with x = 0.27 (i.e., Ba5.19Nd8.54Ti18O54) exhibited a Seebeck coefficient of S1000K = 210 µV/K, electrical conductivity of σ1000K = 60 S/cm, and thermal conductivity of k1000K = 1.45 W/(m K), leading to a ZT value of 0.16 at 1000 K. © 2015 The Author(s) Source

Prytuliak A.,European Space Agency | Godlewska E.,AGH University of Science and Technology | Mars K.,AGH University of Science and Technology | Berthebaud D.,Laboratoire CRISMAT
Journal of Electronic Materials | Year: 2014

The crystal structure of Ag-doped Mg2Si was investigated using synchrotron and neutron powder diffraction analysis, including in situ synchrotron x-ray powder diffraction patterns, recorded during a thermal cycle from room temperature up to 600°C. Rietveld refinement of diffraction patterns indicated that Ag doping results in partial substitution at Si sites. During heating, the Mg2Si lattice parameters exhibited a shift in the temperature dependence at 300°C to 350°C, which was attributed to Ag precipitation out of Mg2Si1−xAgx solid solution. In turn, an increase of the Ag present in the Mg2Si lattice after 350°C could be linked to thermally activated diffusion of Ag from β-AgMg phase. The Ag-dopant migration may explain previously outlined instabilities in the thermopower of Ag-doped Mg2Si, e.g., the drop of the Seebeck coefficient value after heating to 150°C to 200°C and its subsequent increase after 350°C to 450°C. © 2014, European Union. Source

Brard Y.,Laboratoire CRISMAT | Fjellvg H.,University of Oslo | Hauback B.,Institute for Energy Technology of Norway
Solid State Communications | Year: 2011

Presently, the crystal structure and magnetic properties of Sc 2-xFexO3 samples are described for 0.0≤x≤1.0. The cubic bixbyite structure (space group: Ia-3) prevails for all compositions. Excellent homogeneity of the samples was confirmed by energy dispersive spectroscopy analysis performed with a Transmission Electron Microscope. The crystal structure of ScFeO3 was determined by combined refinements of powder X-ray and neutron diffraction data. The magnetic behavior is typical of a frustrated system and no long range order prevails at 9 K. © 2010 Elsevier Ltd. All rights reserved. Source

Savary E.,Laboratoire CRISMAT | Marinel S.,Laboratoire CRISMAT | Gascoin F.,Laboratoire CRISMAT | Kinemuchi Y.,Japan National Institute of Advanced Industrial Science and Technology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

Non-ohmic properties of doped zinc oxide are widely used in varistors applications. It is well established that final properties of the component are strongly correlated with reactivity of the added phases during sintering process and with final microstructure. In this paper, the specific effects of the hybrid single-mode microwave sintering process on the microstructure and electrical properties of a ZnO-based composition are investigated. Nano-sized ZnO-based powder with a proper amount of Bi2O3, Sb 2O3, CoO and MnO is synthesized by a liquid route and is sintered within a short time (less than 10 min) in a conventional (CV) or by an hybrid single-mode microwave (MW) furnaces. Distinct differences can be seen in the density, reaction kinetics and dopant diffusivity: higher kinetics of MW leads to denser pellet, faster reaction among dopants and faster diffusion of cobalt and manganese into ZnO grains although grain sizes are almost identical between CV and MW. These differences in terms of chemistry and microstructure lead to sharp contrasts in electrical properties. © 2011 Elsevier B.V. All rights reserved. Source

Demont A.,University of Liverpool | Sayers R.,University of Liverpool | Tsiamtsouri M.A.,University of Liverpool | Romani S.,University of Liverpool | And 9 more authors.
Journal of the American Chemical Society | Year: 2013

Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO3 perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO3 network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO 3 network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation. © 2013 American Chemical Society. Source

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