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Markovich V.,Ben - Gurion University of the Negev | Fita I.,Polish Academy of Sciences | Wisniewski A.,Polish Academy of Sciences | Puzniak R.,Polish Academy of Sciences | And 5 more authors.
IEEE Transactions on Magnetics | Year: 2017

Magnetic and structural properties of CaMn1-xRexO3 (0.02 ≤ x ≤ 0.1) have been investigated. Substitution of Re5+ ion for the Mn4+ site of 3 generates Mn3+ ions according to the chemical formula CaMn1-2x 4+Mnx 3+Rex 5+O3, accompanied by an increase of lattice parameters and unit-cell volume with increasing {x}. With increasing doping level x , the magnetic ground state evolves from an antiferromagnetic (AFM) with a weak ferromagnetic (FM) component, for x = 0.02 - 0.06 , to the charge ordered {C} -type AFM state at x = 0.1. Spontaneous magnetization at T = 10 K increases quickly with increasing x , approaches the maximum value of 3.5 eμg for x = 0.04 , and then decreases rapidly to 0.2 eμg for x = 0.1. Anomalous negative magnetization (NM) for x = 0.02 has been observed in the zero-field-cooled and field-cooled (FC) magnetization below the magnetic transition temperature. Exchange bias (EB) effect, manifested by horizontal shift in the hysteresis loops of FC samples, has also been observed. This effect is very small for x = 0.02 , almost zeroes for 0.04, and monotonously increases with increasing x. The EB appears due to low-temperature phase separation into FM clusters and charge-ordered AFM phases. The effect of hydrostatic pressure for all samples revealed a significant increase of the FM phase volume under pressure, linked to both suppression of NM in x = 0.02 sample and reduction of the EB effect in all samples. © 1965-2012 IEEE.


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.


Tsuzuki K.,Tokyo University of Marine Science and Technology | Hara S.,Tokyo University of Marine Science and Technology | Xu Y.,Tokyo University of Marine Science and Technology | Morita M.,Nippon Steel & Sumitomo Metal Corporation | And 5 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2011

For bulk HTS rotating machines, enhancement of the trapped flux is a crucial task to achieve practical applications with high torque density. The increase of critical current density Jc using artificial pinning centers is an efficient technique for the enhancement of the flux trapping properties. We attempted to enhance both Jc and the trapped flux in bulk HTS with magnetic/ ferromagnetic particles additions. Fe-B-Si-Nb-Cr-Cu amorphous alloy, Fe2O3 and CoO particles were introduced into the Gd123 matrix. The melt growth of the single-domain bulks with different magnetic particles was performed in air. Enhancement of the critical current density Jc at 77Kwas derived in the bulks with Fe2O 3 and Fe-B-Si-Nb-Cr-Cu additions, while the superconducting transition temperature of 93 K was not degraded significantly. The experiment of the magnetic flux trapping was then conducted under static magnetic field magnetization with liquid nitrogen cooling. In the bulk with 0.4 mol% of Fe-B-Si-Nb-Cr-Cu, the integrated trapped flux exceeds over 35% compared to the one without magnetic particle addition. On the other hand, the addition of CoO particles resulted in a reduction of both Jc and trapped magnetic flux. Present results indicate that the introduction of magnetic particles gives a significant effect to the flux pinning performance. © 2010 IEEE.


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)


Skomedal G.,University of Agder | Holmgren L.,Termo Gen AB | Middleton H.,University of Agder | Eremin I.S.,RAS Ioffe Physical - Technical Institute | And 9 more authors.
Energy Conversion and Management | Year: 2016

Silicides have attracted considerable attention for use in thermoelectric generators due mainly to low cost, low toxicity and light weight, in contrast to conventional materials such as bismuth and lead telluride. Most reported work has focused on optimizing the materials properties while little has been done on module testing. In this work we have designed and tested modules based on N-type magnesium silicide Mg2(Si-Sn), abbreviated MGS, and P-type Higher Manganese Silicide, abbreviated HMS. The main novelty of our module design is the use of spring loaded contacts on the cold side which mitigate the effect of thermal expansion mismatch between the MGS and the HMS. We report tests carried out on three modules at different temperatures and electric loads. At a hot side temperature of 405 °C we obtained a maximum power of 1.04 W and at 735 °C we obtained 3.24 W. The power per thermoelectric material cross section area ranged from 1 to 3 W cm- 2. We used the modeling tool COMSOL to estimate efficiencies at 405 and 735 °C and obtained values of 3.7% and 5.3% respectively - to our knowledge the highest reported value to date for silicide based modules. Post-test examination showed significant degradation of the N-type (MGS) legs at the higher hot side temperatures. Further work is underway to improve the lifetime and degradation issues. © 2015 Elsevier Ltd.


Srivastava D.,University of Manchester | Norman C.,University of Manchester | Azough F.,University of Manchester | Schafer M.C.,Laboratoire CRISMAT | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2016

Ceramics based on Sr0.8La0.067Ti0.8Nb0.2O3-δ have been prepared by the mixed oxide route. The La1/3NbO3 component generates ∼13.4% A-site vacancies; this was fixed for all samples. Powders were sintered under air and reducing conditions at 1450 to 1700 K; products were of high density (>90% theoretical). Processing under reducing conditions led to the formation of a Ti1-xNbxO2-y second phase, core-shell structures and oxygen deficiency. X-ray diffraction (XRD) confirmed a simple cubic structure with space group Pm3m. Transmission electron microscopy revealed a high density of dislocations while analytical scanning transmission electron microscopy at atomic resolution demonstrated a uniform distribution of La, Nb and vacancies in the lattice. X-ray photoemission spectroscopy and thermogravimetry showed the oxygen deficiency (δ value) to be ∼0.08 in reduced samples with enhanced carrier concentrations ∼2 × 1021 cm-3. Both carrier concentration and carrier mobility increased with sintering time, giving a maximum figure of merit (ZT) of 0.25. Selective additional doping by La or Nb, with no additional A site vacancies, led to the creation of additional carriers and reduced electrical resistivity. Together these led to enhanced ZT values of 0.345 at 1000 K. The contributions from oxygen vacancies and charge carriers have been investigated independently. © 2016 the Owner Societies.


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.


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.


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.

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