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Impedance and modulus spectroscopic studies on 40PrTiTaO6 + 60YTiNbO6 ceramic composite

Authors D. B. Dhwajam, M. Buchi Suresh, U. S. Hareesh, J. K. Thomas, S. Solomon, Annamma John
Journal of Materials Science: Materials in Electronics
Volume: 23, Issue: 3, Pages: 653-658
Time of Publication: 2012-03
Abstract The 40PrTiTaO6 + 60YTiNbO6 ceramic composite is prepared through the solid state ceramic route. The structure is discussed using X-ray diffraction analysis. Surface morphology is examined by Scanning Electron Microscopy (SEM). Impedance and modulus spectroscopic studies are carried out. A decrease in the resistive behavior of the sample assisted by the grain boundary conduction with rise in temperature is found. The experimental results on electrical properties indicate that the material exhibits conduction both due to bulk and grain boundary effect. The microstructure was investigated by SEM micrographs in which grains separated by grain boundaries are visible. There is a probable change in the capacitance values of the material as a function of temperature. The relaxation time is small at higher temperatures than at lower temperatures. The activation energy is found as 1.52 eV, which suggests the possibility of electrical conduction due to the mobility of oxide ions (O2−) or oxide ion vacancies at higher temperature.
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Proton Conductivity in Acceptor-Doped LaVO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
J. Electrochem. Soc.
Volume: 158, Issue: 8, Pages: B857-B865
Time of Publication: 2011-06
Abstract Electrical characterization of nominally undoped LaVO4, La0.99Ca0.01VO4− and La0.95Ca0.05VO4− was performed in various partial pressures of oxygen, water vapor and hydrogen isotopes, from 300 to 1100C by impedance spectroscopy, AC conductivity measurements (10 kHz) and EMF-measurements. XRD, SEM and EDS were used for structural, micro structural and compositional analysis. Acceptor doped LaVO4 is a pure ionic conductor in oxidizing atmospheres in the entire measured temperature range; dominated by proton conductivity at low temperatures (T < 450C) under wet conditions and oxide ion conductivity at high temperatures. A maximum in the partial proton conductivity of ~ 6 10−5 S/cm was reached at 900C (pH2O2.510-2 atm). Thermodynamics of hydration and transport parameters for charge carriers in La0.99Ca0.01VO4 were derived from relations between defect chemistry, transport properties and the measured conductivity data and revealed: S=− 130 10 J/mol K, S =− 142 10 J/mol K, H=− 110 10 kJ/mol, 0,H+ = 50 6 cm2 K/Vs, Hmob,H+ = 75 10 kJ/mol, 0,v= 120 20 cm2 K/Vs and Hmob,v = 85 10 kJ/mol. The tetrahedron (XO4) volume and migration enthalpy were found to be correlated for the series of monoclinic LaXO4.

Nanostructuring phenomena in oxygen-conducting complex oxides of heavy REE

Authors A. V. Shlyakhtina, D. A. Belov, S. Yu. Stefanovich and L. G. Shcherbakova
Russian Journal of Electrochemistry
Volume: 47, Issue: 5, Pages: 620-627
Time of Publication: 2011-05
Abstract In complex oxides of REE (Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), Ln2TiO5 (Ln = Er-Yb)) and Ho2TiO5, the following phase transitions of the order-disorder type are studied for different cooling rates: rhombohedral δ-phase-defective fluorite in Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), pyrochlor-like phasedefective fluoride in Ln2TiO5 (Ln = Er-Yb), and hexagonal β-phase-pyrochlor in Ho2TiO5. The presence of nanostructuring phenomena typical of fluorite-like polymorphous modifications of complex oxides in the Ln2O3-MO2 (Ln = Ho-Lu; M = Ti, Zr, Hf) systems is confirmed. The conductivity of polymorphous modifications of Ln4Zr3O12 (Ln = Tm, Lu;) and Ln2TiO5 (Ln = Ho-Yb) with different thermal prehistory is studied. The comparative studies of the oxygen-ionic conductivity of fluorite- and pyrochlor-like Ln2TiO5 (Ln = Ho-Yb), pyrochlor Ho2TiO5, and β-Ho2TiO5 and also of the conductivity of fluorite-like compounds and δ-Ln4Zr3O12 (Ln = Tm, Lu) are carried out. The oxygen-ionic conductivity of complex oxides in the Ln2O3-MO2 (Ln = Er-Lu; M = Ti, Zr, Hf) system is shown to decrease in the following series: defective pyrochlor-defective fluorite-rhombohedral δ-phase ∼ hexagonal β-phase.

Partial Oxidation of Methane and Oxygen Permeation in SrCoFeOx Membrane Reactor with Different Catalysts

Author Jay Kniep and Y.S. Lin
Ind. Eng. Chem. Res.
Volume: 50, Issue: 13, Pages: 7941–7948
Time of Publication: 2011-05
Abstract Partial oxidation of methane (CH4) and oxygen permeation in a dense SrCoFeOx disk membrane reactor were studied with the reducing side of the membrane packed with different catalysts (catalyst support γ-Al2O3, La0.6Sr0.4Co0.8Fe0.2O3−δ, and 10 wt % Ni/γ-Al2O3) of increasing reaction activities for CH4 oxidation. The influence of temperature, flow rates, and inlet CH4 concentration (diluted with helium) on the performance of the different membrane reactors was investigated. The oxygen permeation flux and CH4 conversion increased in the following order: γ-Al2O3 < La0.6Sr0.4Co0.8Fe0.2O3−δ < 10% Ni/γ-Al2O3. The membrane reactor with the reforming catalyst of 10 wt % Ni/γ-Al2O3 had the highest CH4 conversion (90%), CO selectivity (97%), and oxygen permeation flux (2.40 mL/(cm2 min)) at 900 C. The improvement of the oxygen permeation through the membranes with different catalysts emphasizes the effect of the CH4 oxidation reaction rate on the reducing side of the membrane on the oxygen permeation flux through the mixed-conducting ceramic membranes. Under identical conditions, the oxygen permeation flux through mixed-conducting ceramic membrane with a reducing gas is a strong function of the catalytic activity for the oxidation of the reducing gas.
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Phase transition and electrical properties of gallium- and indium-doped Bi10Ti3W3O30

Authors E. P. Kharitonova, D. A. Belov, A. V. Mosunov and V. I. Voronkova
Inorganic Materials
Volume: 47, Issue: 5, Pages: 513-520
Time of Publication: 2011-05
Abstract Polycrystalline samples of gallium- and indium-doped Bi10Ti3W3O30 (mixed-layer Aurivillius phase with the Ti4+ and W6+ distributed at random over the perovskite-like slabs) have been prepared by solid-state reactions, and their polymorphism and electrical properties have been studied. Doping with both In3+ and Ga3+ yields limited solid solutions and shifts the ferroelectric phase transition to lower temperatures. The heterovalent substitutions of In3+ and Ga3+ for Ti4+ and W6+ increase the oxygen vacancy concentration and, accordingly, the conductivity of the material relative to the undoped compound.

Lamellar Titanates: A Breakthrough in the Search for New Solid Oxide Fuel Cell Anode Materials Operating on Methane

Authors Cdric Prillat-Merceroz, Pascal Roussel, Rose-Nolle Vannier, Patrick Glin, Sbastien Rosini, Gilles Gauthier
Advanced Energy Materials
Volume: 1, Issue: 4, Pages: 573–576
Time of Publication: 2011-07
Abstract Decreasing the dimensionality of the LaxSr1–xTiOmath image family structure from 3D to 2D by increasing the La content greatly enhances the electrochemical performance of the material as an SOFC anode. This is attested to by the strong decrease in the polarization resistance values deduced from the complex impedance spectra (Nyquist plot) recorded at 900 C in H2/H2O(3%) on a symmetrical cell.
Keywords Solid oxide fuel cells; Anode materials; Titanate; Methane
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An ion-plasma technique for formation of anode-supported thin electrolyte films for IT-SOFC applications

Authors N.S. Sochugov, A.A. Soloviev, A.V. Shipilova, V.P. Rotshtein
International Journal of Hydrogen Energy
Volume: 36, Issue: 9, Pages: 5550-5556
Time of Publication: 2011-05
Abstract This paper describes a preparation method and structural and electrochemical properties of a thin bilayer anode-electrolyte structure for a solid oxide fuel cell operating at intermediate temperatures (IT-SOFC). Thin anode-supported yttria-stabilized zirconia electrolyte films were prepared by reactive magnetron sputtering of a Zr–Y target in an Ar–O2 atmosphere. Porous anode surfaces of IT-SOFCs were modified by a pulsed low-energy high-current electron beam prior to film deposition; the influence of this pretreatment on the performance of both the deposited films and a single cell was investigated. The optimal conditions of the pulsed electron beam pretreatment were obtained. For the electrolyte thickness about 2.5 μm and the value of gas permeability of the anode/electrolyte structure 1.01 10−7 mol m−2 s−1 Pa−1, the maximum power density achieved for a single cell at 800 C and 650 C was found to be 620 and 220 mW cm−2 in air, respectively.
Keywords Solid oxide fuel cell; YSZ electrolyte; Magnetron sputtering; Surface modification of material; Pulsed electron beam treatment; Electrical performance

Microwave-assisted synthesis of gadolinia-doped ceria powders for solid oxide fuel cells

Authors A. Gondolini, E. Mercadelli, A. Sanson, S. Albonetti, L. Doubova and S. Boldrini
Ceramics International
Volume: 37, Issue: 4, Pages: 1423-1426
Time of Publication: 2011-05
Abstract Gadolinia doped ceria (GDC) is an attractive electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) for its high ionic conductivity at low temperature (500–700 C). A number of different methods are currently used to prepare nano-sized doped-ceria powder. Among the others, precipitation in solution remains the best method to obtain well-dispersed particles of controlled properties. In this work, nanocrystalline Ce1−xGdxO2−δ (GDC) particles were produced by polyol microwave assisted method in very mild conditions (170 C, 2 h, 1 atm). The as-synthesized powder showed good sinterability and ionic conductivity comparable to the ones of the corresponding nanometric commercial GDC.
Keywords GDC; Microwave heating; Polyol method; IT-SOFC

Solid oxide fuel cells with Sm0.2Ce0.8O2−δ electrolyte film deposited by novel aerosol deposition method

Authors Sea-Fue Wang, Yung-Fu Hsu, Chih-Hao Wang and Chin-Ting Yeh
Journal of Power Sources
Volume: 196, Issue: 11, Pages: 5064-5069
Time of Publication: 2011-06
Abstract In this study, dense electrolyte ceramic Sm0.2Ce0.8O2−δ (SDC) thin films are successfully deposited on NiO-SDC anode substrate by aerosol deposition (AD) with oxygen as the carrier gas at the substrate temperature ranging from room temperature to 300 C. To remove the effect of humidity on the starting powders, this study found that, in depositing SDC films, having the starting powders preheat-treated at 200 C helped generate a smooth and dense layer, though a lower deposition rate was achieved. At a deposition time of 22 min, SDC films with a uniform thickness of 1.5 μm and grain sizes of ≈67 nm are obtained. SOFC single cells are then built by screen printing a LSCF cathode on the anode-supported substrates with SDC electrolyte. The cross-sectional SEM micrographs exhibit highly dense, granular, and crack-free microstructures. The open circuit voltages (OCV) of the single cells decrease with the rise in temperature, dropping from 0.81 V at 500 C to 0.59 V at 700 C. Maximum power densities (MPD) decline with decreasing operating temperature from 0.34 to 0.01 W cm−2 due to the increase of the R0 and RP of the single cells. The electrochemical results testify to the fine quality of SDC films as well as illustrate the electrolyte thickness effect and the effect of mixed ionic and electronic conduction of the SDC electrolyte in the reducing atmosphere.
Keywords SDC films, NiO-SDC substrate, aerosol deposition, Very dense SDC films, uniform thickness of 1.5 μm, Single cell with a MPD of 0.34 W cm−2, 700 C, Solid oxide fuel cell; Ceria; Aerosol deposition; Electrolyte

Conductivity, transport number measurements and hydration thermodynamics of BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ)

Authors S. Ricotea, The Corresponding Author, N. Bonanos, H.J. Wang and R. Haugsrud
Solid State Ionics
Volume: 185, Issue: 1, Pages: 11-17
Time of Publication: 2011-03
Abstract BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ) compounds with ξ = 0.01 and 0.02 have been synthesized by solid state reaction at 1400 C and sintered at 1450 C. TEM analyses were performed and showed a segregation of nickel at the grain boundaries for ξ = 0.02. This apparent solubility limit of Ni in the B-site of the perovskite is in agreement with similar data obtained earlier for the two compositions. The first aim of this work was to evaluate the conductivity of BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ) at temperature between 500 and 900 C, using impedance spectroscopy at different oxygen partial pressures and water vapor pressures, as well as the emf technique. The compounds exhibit p-type conduction in oxidizing atmosphere, and ionic conduction elsewhere. The oxide ion contribution of the conductivity is negligible only for temperatures below 600 C. The determination of hydration enthalpies, our second goal, was achieved by modelling of the conductivity data and by thermogravimetric measurements (TG-DSC).

Fabrication and Characterization of Anode-Supported BaIn0.3Ti0.7O2.85 Thin Electrolyte for Solid Oxide Fuel Cell

Authors M. Rieu, P. K. Patro, T. Delahaye*, E. Bouyer
International Journal of Applied Ceramic Technology
Article first published online: 28 MAR 2011
Time of Publication: 2011-03
Abstract BaIn0.3Ti0.7O2.85 (BIT07) is a promising electrolyte for solid oxide fuel cells, due to its chemical compatibility with most of the cathode electrode material such as LSM and Ln2NiO4. The present work is aimed on the fabrication of anode-supported half cells with thin BIT07 electrolyte. For this, Ni-8YSZ cermet was chosen due to its excellent mechanical and electrochemical properties, in addition to its low cost. The NiO–8YSZ anode support was prepared by tape casting, and for this, an organic slurry formulation was optimized. The BIT07 electrolyte thin film was deposited through screen printing on the green anode. The formulation of the ink was optimized, and sintering at 1350C for 3 h led to a dense electrolyte with controlled thickness varying from 2 to 12 μm. Further, the cermet electrode still had a homogeneous microstructure with well-defined anode/electrolyte interface. The electrode ASR was about 0.5 Ω cm2 and was stable over 500 h at 800C under H2–3% H2O. The fabrications of half cells were successfully scaled up to 100 mm 100 mm retaining the dimensional control and without any surface defects.

Curing of a network polyimide modified with a linear component

Authors D.A. Belov, S.Yu. Stefanovich, M.Yu. Yablokova
Russian Journal of Applied Chemistry
Volume: 84, Issue: 2, Pages: 301-306
Time of Publication: 2011-03
Abstract The curing and relaxation processes in polymeric composites based on blends of network and linear polyimides applied onto a filler were studied by dielectric spectroscopy. The sensitivity of dielectric spectroscopy to processes occurring in the course of curing was examined.

Structure, Water Uptake, and Electrical Conductivity of TiP2O7

Authors Vajeeston Nalini, Magnus H. Srby, Koji Amezawa, Reidar Haugsrud, Helmer Fjellvg, Truls Norby
Journal of the American Ceramic Society
Volume: 94, Issue: 5, Pages: 1514–1522
Time of Publication: 2011-05
Abstract We report here on the structure of TiP2O7 and electrical properties of nominally acceptor (Sc, Fe)-doped TiP2O7 synthesized by an aqueous phosphoric acid route. Structural characterization, including studies of the high-temperature phase transition in TiP2O7, was carried out by powder X-ray and neutron diffraction. Ceramic disks were sintered by the spark plasma technique and their conductivities were characterized as a function of p(O2) and p(H2O) in the temperature range of 500–1000C by means of AC constant frequency measurements and impedance spectroscopy. As reported earlier, the acceptor doping appears not to influence the defect structure of TiP2O7 significantly. Effects of H+/D+ isotope shift were utilized to identify proton conduction. The conductivity was independent of p(O2) at 500–900C under oxidizing conditions suggesting predominantly protonic conduction at these temperatures. Under reducing atmosphere n-type conductivity contributed to the total conductivity at the higher temperatures. p(H2O) dependencies of the conductivities are interpreted in terms of a defect-chemical model involving protons and oxygen interstitials as the dominating defects. The uptake of water was studied by thermogravimetry at high p(H2O) and the thermodynamics of the hydration reaction was derived. Finally, parameters for the mobility of protons were extracted by combining the conductivity and thermogravimetry data.
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Microstructural characterization and electrical properties of spray pyrolyzed conventionally sintered or hot-pressed BaZrO3 and BaZr0.9Y0.1O3 − δ

Authors Paul Inge Dahl, Hilde Lea Lein, Yingda Yu, Julian Tolchard, Tor Grande, Mari-Ann Einarsrud, Christian Kjlseth, Truls Norby and Reidar Haugsrud
Solid State Ionics
Volume: 182, Issue: 1, Pages: 32-40
Time of Publication: 2011-02
Abstract A spray pyrolysis route to BaZrO3 (BZ) and BaZr0.9Y0.1O2.95 (BZY) powders was developed starting from nitrate solutions. Homogeneous powders with a grain size of ~ 100 nm were achieved. A calcination of the powder was necessary to remove carbonates formed during the spray pyrolysis. Hot pressing was in comparison with conventional sintering more effective to enhance densification and suppress grain growth, and dense (> 96%) materials with homogeneous microstructure were obtained. The Y-substitution decreased the densification rate. Minor amounts of a secondary phase was observed at the grain boundary triple points of BZY, but the grain boundaries were otherwise found to be coherent and without significant secondary phase accumulation. Impedance spectroscopy vs T, pO2 and pH2O of conventionally sintered BZ and hot-pressed BZY demonstrated that the conductivity of BZ was orders of magnitude lower than compared to BZY. The conductivity of BZ displayed mixed proton and p-type electronic conduction characteristics in the grain interior which was depressed at the grain boundaries. The grain boundaries showed an additional n-type electronic conduction under reducing conditions. The conductivity characteristics were according to core-space charge layer theory. BZ seems to exhibit a larger ratio of p-type electronic to protonic conduction as compared to BZY, contrary to the prediction of simple defect chemistry.

BiFeO3–PbZrO3–PbTiO3 ternary system for high Curie temperature piezoceramics

Authors Wei Hu, Xiaoli Tan and Krishna Rajan
Journal of the European Ceramic Society
Volume: 31, Issue: 5 Time of Publication: 2011-05
Abstract BiFeO3–PbZrO3–PbTiO3 ternary solid solution system was investigated for the development of piezoelectric ceramics with high Curie temperatures. The search for the morphotropic phase boundary (MPB) compositions in this ternary system started from mixing two MPB compositions: 0.70BiFeO3–0.30PbTiO3 and 0.52PbZrO3–0.48PbTiO3. The content of PbTiO3 was then further fine tuned in order to reach the appropriate volume fraction between the rhombohedral and tetragonal phases in the sintered ceramics. It was observed that the sintering temperature has a profound impact on the density, grain morphology, dielectric and ferroelectric properties of the ceramics. The composition that displays the best combined structure and properties was identified to be 0.648BiFeO3–0.053PbZrO3–0.299PbTiO3, with a Curie temperature TC of 560 C, a remanent polarization Pr of 15.0 μC/cm2, and a piezoelectric coefficient d33 of 64 pC/N.

Synthesis and characterization of Ca-substituted YAlO3 by pechini route for solid oxide fuel cells

Authors Ramya Hariharan, Prakash Gopalan
Solid State Sciences
Volume: 13, Issue: 1, Pages: 168-174
Time of Publication: 2011-01
Abstract The high operating temperature requirement of solid oxide fuel cells demands electrolyte materials stable at temperatures around 800 C. The perovskite material YAlO3, with yttrium ion on the A-site and the aluminium ion on the B-site is being investigated as an electrolyte for solid oxide fuel cells. This work investigates the structure and electrical conductivity of undoped and Ca-doped YAlO3 compositions that has been synthesized by the Pechini route. The samples have been investigated by X-ray diffraction studies. The electrical conductivity studies have been performed using a.c impedance spectroscopy in the range 200–800 C in air. The doped YAlO3 of composition x = 0.1 exhibits a total conductivity of about 2.2 mS/cm at 800 C. The microstructural evaluation of the samples has been conducted by scanning electron microscopy coupled with energy dispersive spectrum analysis.

δ-Phase to defect fluorite (order–disorder) transition in the R2O3–MO2 (R = Sc; Tm; Lu; M = Zr; Hf) systems

Authors A.V. Shlyakhtina, D.A. Belov, S.Yu. Stefanovich, I.V. Kolbanev, O.K. Karyagina, A.V. Egorov, S.V. Savilov and L.G. Shcherbakova
Materials Research Bulletin
Volume: 46, Issue: 4, Pages: 512–517
Time of Publication: 2011-04
Abstract We have studied the δ-phase to defectfluoriteF* (order–disorder) transition in the R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) compounds. The temperature of the δ–F* phasetransition in Tm4Zr3O12 is ∼1600 C. The rate of this transition in R4Zr3O12 (R = Sc, Tm, Lu) decreases markedly with decreasing difference in ionic radius between the R3+ and Zr4+, leading to stabilization of the δ-phasesR4Zr3O12 with R = Sc and Lu at high temperatures (∼1600 C). During slow cooling (5 C/h), the high-temperature defectfluoritesF*-R2Hf2O7 (R = Tm, Lu) decompose reversibly to form the δ-phasesR4Hf3O12. Some of the materials studied exhibit microdomains formation effects, typical of the fluorite-related oxide compounds in the R2O3–MO2 (M = Ti, Zr, Hf) systems of the heavy rare earths. The high-temperature defectfluoritesF*-R4M3O12 (R = Tm, Lu; M = Zr, Hf) as a rule contain antiphase microdomains of δ-R4Zr3O12. After slow cooling (5 C/h), such microdomains are large enough for the δ-phase to be detected by X-ray diffraction. The conductivity data for R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) and Ln2Hf2O7 (Ln = Dy, Lu) prepared by different procedures show that the rhombohedral phasesδ-R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) are poorer conductors than the defectfluorites, with 740 C conductivity from 10−6 to 10−5 S/cm. The conductivity drops with decreasing rare-earth ionic radius and, judging from the Ea values obtained (1.04–1.37 eV), is dominated by oxygen ion transport. The highest conductivity, ∼6 10−4 S/cm at 740 C, is offered by the rapidly cooled F*-Dy2Hf2O7. In the fluorite homologous series, oxygen ion conductivity decreases in the orderdefect pyrochlore > defectfluorite > δ-phase.
Keywords Fluorite; δ-Phases R4M3O12; Pyrochlore; Order–disorder transition; Antiphase microdomains; High-temperature conductivity
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Polymorphism and high-temperature conductivity of Ln2M2O7 (Ln = Sm─Lu; M = Ti, Zr, Hf) pyrochlores

Authors A.V. Shlyakhtina, L.G. Shcherbakova
Solid State Ionics
Volume: 192, Issue: 1, Pages: 200–204
Time of Publication: 2011-06
Pyrochlore; Fluorite; Order─disorder; Defects; High-temperature conductivity; Ionic conductivity; Solid electrolyte

Proton conductivity in Sm2Sn2O7 pyrochlores

Authors K.E.J. Eurenius, E. Ahlberg and C.S. Knee
Solid State Ionics
Volume: 181, Issue: 35-36, Pages: 1577-1585
Time of Publication: 2010-11
Abstract The electrical conductivity of the pyrochlore systems, Sm2Sn2O7, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ was studied using impedance spectroscopy under wet and dry gas (O2 and Ar) in the temperature range 150–1000 C. Enhancements of the bulk conductivity of all samples at temperatures up to ~ 550 C were observed for wet conditions consistent with significant levels of proton conduction. The presence of dissolved protons in the acceptor-doped materials, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ, is supported by infrared spectroscopy and thermogravimetric analysis. Proton conduction was confirmed by isotope effects under heavy water (O2/D2O and Ar/D2O). The A-site substituted sample Sm1.92Ca0.08Sn2O7 − δ yielded the highest levels of proton conduction and displayed mixed ionic and electronic conduction under dry oxidising conditions. Electron hole conduction dominates in dry oxygen for Sm2Sn1.92Y0.08O7 − δ and Sm2Sn2O7. For the A-site doped sample bulk and grain boundary conduction could be separated. The specific grain boundary conduction was calculated using the brick layer model and was found to be two orders of magnitude lower compared to the bulk conductivity. The unexpected increase in conductivity seen for the undoped sample under wet gas is discussed in the context of structural disorder and possible filling of the un-occupied anion site in the pyrochlore structure by OH-groups.
Keywords Sm2Sn2O7; Proton conductor; Pyrochlore; Oxide ion conductivity; p-type conductivity; Infra-red spectroscopy; Thermogravimetric analysis

Experimental and theoretical studies of hydrogen permeation for doped strontium cerates

Authors Maki Matsuka, Roger D. Braddock, Hiroshige Matsumoto, Takaaki Sakai, Igor E. Agranovski and Tatsumi Ishihara
Solid State Ionics
Volume: 181, Issue: 29-30, Pages: 1328-1335
Time of Publication: 2010-09
Abstract Non-galvanic hydrogen permeation properties of SrCe0.95Yb0.05O3 − α (SCYb-5) and SrCe0.95Tm0.05O3 − α (SCTm-5) dense membranes were investigated in a ‘wet’ hydrogen atmosphere where water vapour partial pressures were well defined and monitored for the entire duration of the experiments. The theoretical modelling of hydrogen permeation flux for SCYb-5 and SCTm-5 was also undertaken, and compared with experimental results. The parameter tuning was also performed by fitting the model to the experimental data obtained in this study. The experimental hydrogen permeation flux for SCYb-5 and SCTm-5 dense membranes was 6.8e− 9 mol/cm2/s and 7.1e− 9 mol/cm2/s, respectively, under the upstream hydrogen partial pressure of 0.25 atm (25%H2/Ar) at 900 C. As expected, the hydrogen permeation flux increases with the increase in the upstream hydrogen partial pressures, reaching the maximum flux of 1.4e− 8 mol/cm2/s and 1.6e− 8 mol/cm2/s, for SCYb-5 and SCTm-5 respectively, under the upstream hydrogen partial pressure of 1 atm (100%H2) at 900 C. Previous modelling used hydrogen permeation data collected by others in a permeation test conducted in a ‘dry’ hydrogen atmosphere (with unknown water vapour pressures). The modelled hydrogen permeation flux agreed well with the experimental data attained in this study, for both SCYb-5 and SCTm-5 samples. The parameter tuning further improved the model predictions for those samples. It was apparent that the modelled hydrogen flux agreed better with the experimental data obtained in this study (i.e. in a wet hydrogen atmosphere with known water vapour pressures).
Keywords Dense ceramic membranes; Hydrogen permeation; Modelling

Directed integration of ZnO nanobridge sensors using photolithographically patterned carbonized photoresist

Authors Chien-Chih Huang, Brian D Pelatt and John F Conley Jr
Volume: 21, Issue: 19 Time of Publication: 2010-05
Abstract A method for achieving large area integration of nanowires into electrically accessible device structures remains a major challenge. We have achieved directed growth and integration of ZnO nanobridge devices using photolithographically patterned carbonized photoresist and vapor transport. This carbonized photoresist method avoids the use of metal catalysts, seed layers, and pick and place processes. Growth and electrical connection take place simultaneously for many devices. Electrical measurements on carbonized photoresist/ZnO nanobridge/carbonized photoresist structures configured as three-terminal field effect devices indicate bottom gate modulation of the conductivity of the n-type ZnO channel. Nanobridge devices were found to perform well as ultraviolet and gas sensors, and were characterized as regards ultraviolet light pulsing, oxygen concentration, and humidity. The sensitivity of the three-terminal nanobridge sensors to UV light and oxygen was enhanced by application of a negative bottom gate voltage.

Yttria-stabilized zirconia thin film electrolyte produced by RF sputtering for solid oxide fuel cell applications

Authors Federico Smeacetto, Milena Salvo, Lakshmi Chandru Ajitdoss, Sergio Perero, Tomasz Moskalewicz, Stefano Boldrini, Lioudmila Doubova and Monica Ferraris
Materials Letters
Volume: 64, Issue: 22, Pages: 2450-2453
Time of Publication: 2010-11
Abstract Thin film (40–600 nm) yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC) were deposited on NiO-YSZ anodes and fused silica substrates by RF sputtering, using low applied power without the use of post deposition annealing heat treatment. YSZ film showed a nanocrystalline structure and consisted of the Zr.85Y.15O1.93 (fcc) phase. The film was dense and the YSZ/anode interface was continuous and crack free. According to preliminary in-plane conductivity measurements (temperature range 550–750 C) on the YSZ film, the activation energy for ionic conduction was found to be 1.18 0.01 eV.
Keywords Thin films; Ceramics; Microstructure; Nanomaterials

High-temperature proton conductivity and defect structure of TiP2O7

Authors Vajeeston Nalini, Reidar Haugsrud and Truls Norby
Solid State Ionics
Volume: 181, Issue: 11-12, Pages: 510-516
Time of Publication: 2010-04
Abstract Nominally undoped TiP2O7 and TiP2O7 with 2 mol-% substitution of Ti by Al were synthesized from TiO2 (Al2O3) and H3PO4(aq), sintered at 1050 C, and characterized by XRD, TEM and SEM. The electrical conductivity was investigated at 300–1000 C as a function of p(O2), p(H2O), and p(D2O). The material's phase transition around 700 C is clearly visible in the conductivity curves. Al substitution hardly increased the conductivity. The conductivity was higher in H2O- than in D2O-containing and dry atmospheres, indicating the dominance of proton conduction. The conductivity was accordingly mainly independent of p(O2). A slight increase in the conductivity with decreasing p(O2) at the highest temperatures was indicative of a minor contribution of n-type electronic conduction. The p(H2O) and temperature dependencies of the conductivity have been modelled as a sum of proton and electron partial conductivities under a situation with protons charge compensated by oxygen interstitials as dominating defects.
Keywords Titanium pyrophosphate; TiP2O7; Al-substituted TiP2O7; Proton conduction; Defect structure

Scandium stabilized zirconium thin films formation by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis, Oresta Katkauskė and Darius Milčius
Solid State Ionics
Volume: 184, Issue: 1, Pages: 10–13
Time of Publication: 2011-03
Abstract Scandiumstabilizedzirconium (10ScSZ) thin ceramic films were deposited by e-beam evaporation of (ZrO2)0.90(Sc2O3)0.10 micro powder (particle size 0.5 0.7 μm). The influence of deposition rate on formed thinfilms microstructure and electrical properties was studied. 10ScSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy-600 (Fe–Ni–Cr) substrates. Deposition rate was changed from 2 to 16 /s to test its influence on thinfilmformation and its properties. The microstructure of formed 10ScSZ thin ceramic films was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical parameters of formed thin ceramics were investigated in the frequency range from 0.1 Hz to 1.0 MHz (in temperature range from 473 to 873 K). The ionic conductivity of the deposited electrolyte 10ScSZ thinfilms was determined by impedance spectroscopy. It was determined that the deposition rate (in range from 2 to 16 /s) has influence on crystallite size. It increases by increasing the deposition rate from 18.4 to 26.9 nm. The XRD measurements show that the formed 10ScSZ thinfilms do not repeat the crystallographic phase of the initial evaporated powder material—it is changes from rhombohedra (initial powder) to cubic (the formed thinfilms).
Keywords Scandium stabilized zirconium (ScSZ); Ionic conductivity; Electron beam deposition; Solid oxide fuel cells (SOFC)
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Effect of sintering temperature and sintering additives on ionic conductivity of LiSi2N3

Authors Eiichirou NARIMATSU, Yoshinobu YAMAMOTO, Toshiyuki NISHIMURA and Naoto HIROSAKI
Journal of the Ceramic Society of Japan
Volume: 118 , Issue: 1381 , Pages: 837-841
Time of Publication: 2010-09
Abstract The effect of sintering temperature and sintering additives on the ionic conductivity of LiSi2N3 was studied by performing complex impedance measurements. LiSi2N3 materials were fabricated by the reaction of Li3N, Si3N4, and sintering additives at temperatures of 1873–2073 K. Dense hot-pressed bodies were obtained at 1973–2073 K in the case of undoped LiSi2N3 and at 1873 K in the case of Y2O3, CaF2, and B2O3 addition. The ionic conductivity increased greatly with increasing sintering temperature and exhibited a strong dependence on the type of sintering additive. When the sintering temperature was constant at 1873 K, although the conductivities of Y2O3-doped LiSi2N3 and CaF2-doped LiSi2N3 were lower than that of undoped LiSi2N3, the conductivity of B2O3-doped LiSi2N3 was higher than that of undoped LiSi2N3. The enhanced conductivity of B2O3-doped LiSi2N3 can be attributed to the increase in the density of the sintered material without the formation of a phase of significant resistance at the grain boundaries.
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