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H and Li Related Defects in ZnO and their Effect on Electrical Properties

Authors Tor Svendsen Bjrheim , Skjalg Erdal , Klaus Magnus Johansen , Knut Erik Knutsen , and Truls Norby
Source
J. Phys. Chem. C
Volume: 166, Issue: 44, Pages: 23764–23772
Time of Publication: 2012-10
Abstract Li and H are important electrically active impurities in ZnO and this work presents a detailed experimental and computational study of the behavior of H and Li in ZnO, and their effect on its defect structure. We employ AC conductivity measurements as a function of temperature and partial pressure of O2, H2O and D2O, which is combined with first principles density functional theory (DFT) calculations and thermodynamic modeling (TDM) of finite temperature defect structures in undoped and Li doped ZnO. Undoped ZnO is dominated by protons as hydroxide defects (OH_O^•), oxygen vacancies (v_O^(••)) and electrons under a large variety of atmospheric conditions, and we also predict from DFT and TDM the substitutional hydride ion (H_O^•) to dominate concentration-wise under the most reducing conditions at temperatures above 500 C. The equilibrium concentrations of defects in ZnO are small, and dopants such as Li strongly affect the electrical properties. Experimentally, Li doped ZnO is found to be n-type under all available atmospheric conditions and temperatures, with a n-type conductivity significantly lower than that of as-grown ZnO. The n-type conductivity also increases with decreasing p_(O_2 ) and with increasing p_(H_2 O). The observed electrical properties of Li doped ZnO are attributed to dominance of the ionic defects Li_Zn^/, OH_O^•, Li_i^•, v_O^(••), and the neutral complexes (Li_Zn OH_O)^ and (Li_Zn Li_i)^. Although Li doping lowers the Fermi level of as-grown ZnO significantly, low formation energy of the ionic donors, and passivation of Li_Zn^/ in the form of (Li_Zn OH_O)^ and (Li_Zn Li_i)^, prevents realization of significant/stable p-type activity in Li doped ZnO under equilibrium conditions.
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Crystal structure, hydration and ionic conductivity of the inherently oxygen-deficient La2Ce2O7

Authors Vasileios Besikiotis, Christopher S. Knee, Istaq Ahmed, Reidar Haugsrud, Truls Norby
Source
Solid State Ionics
Volume: 228, Pages: 1–7
Time of Publication: 2012-11
Abstract The crystal structure, hydration and ionic conductivity of the inherently oxygen deficient La2Ce2O7 system have been investigated. On the basis of Rietveld analysis of neutron diffraction data, the material is found to adopt a cation disordered oxygen-deficient fluorite structure. Impedance spectroscopy, performed in the temperature range 1000–200 C and as a function of water vapor and oxygen partial pressure, suggests that oxide ion conductivity dominates at high temperatures, while protons are the main charge carrier at temperatures below approximately 450 C. Proton conductivity was confirmed by isotope shifts under H2O and D2O. The dissolution of water was measured by means of thermogravimetry (TG). A defect chemical model is developed to derive hydration thermodynamic parameters based on TG and conductivity data. The hydration enthalpy was, moreover, determined directly by simultaneous TG and differential scanning calorimetry (TG–DSC). The TG–DSC values were in good agreement with those modeled from conductivity and TG data.
Keywords La2Ce2O7; Proton conductivity; Pyrochlore structure; Fluorite structure; Nonstoichiometric oxides
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Microstructure and electrical properties of zirconia and composite nanostructured ceramics sintered by different methods

Authors Bogdan Stefan Vasile, Ecaterina Andronescu, Cristina Ghitulica, Otilia Ruxandra Vasile, Lavinia Curechiu, Rares Scurtu, Eugeniu Vasile, Roxana Trusca, Livia Pall, Virgil Aldica
Source
Ceramics International
Volume: 39, Issue: 3, Pages: 2535–2543
Time of Publication: 2013-04
Abstract The aim of this study is the preparation and characterization of dense cubic zirconia ceramics and zirconia nanocomposites (reinforced with 5 wt% alumina). The powders were obtained through sol–gel methods and densified using classical sintering and spark plasma sintering (SPS) methods. The obtained ceramics were characterized through X-ray diffraction, scanning electron microscopy and impedance spectroscopy at room and high temperature. The average grain size of cubic zirconia particles was found to be approximately 8 and 2.5 μm for the classical sintering and 99 nm for SPS. The alumina particles in composites have an average grain size of 0.7 μm for classical sintering and 53 nm for SPS ones. The total conductivity for nanocomposites sintered through both methods was also determined.
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Characteristics of SrCo1 − xSnxO3 − δ cathode materials for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Chun-Ting Yeh, Chien-Chung Huang, Hsi-Chuan Lu
Source
Solid State Ionics
Volume: 227, Pages: 10–16
Time of Publication: 2012-10
Abstract In this study, introduction of tin ions in the SrCoO3 − δ oxide is attempted to modify its electrochemical behavior for serving as a cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Doping of tin ions appears to stabilize the cubic Pm-3m phase of the SrCo1 − ySnyO3 − δ ceramics but generates SrSnO3 precipitates and inhibits the grain growth as y value rises to a level greater than 10%. Obtained at 550 C, the maximum electrical conductivity of SrCo0.95Sn0.05O3 − δ reads 545 S cm− 1. Single cells with a structure of NiO–Sm0.2Ce0.8O2 − δ (SDC)/SDC/SrCo0.95Sn0.05O3 − δ–SDC are built and characterized. Though SrCo0.95Sn0.05O3 − δ is regarded as an MIEC (mixed ionic/electronic conductivity material), adding SDC to SrCo0.95Sn0.05O3 − δ guarantees good adhesion to and fine electrical contact with the electrolyte layer, thereby contributing to the reduction in R0 and RP values. The single cell with the SrCo0.95Sn0.05O3 − δ–SDC composite cathode at 700 C registers respectively an R0 value of 0.044 Ω cm2 and an RP value of 0.109 Ω cm2. In the absence of microstructure optimization and hermetic sealing of cells, a high power density of 0.847 W cm− 2 is reached. SrCo1 − ySnyO3 − δ thus emerges to be a promising cathode material for IT-SOFCs applications.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
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Investigation of La1−xSrxCrO3−∂ (x ~ 0.1) as Membrane for Hydrogen Production

Authors Yngve Larring, Camilla Vigen, Florian Ahouanto, Marie-Laure Fontaine, Thijs Peters, Jens B. Smith, Truls Norby and Rune Bredesen
Source
Membranes
Volume: 2, Issue: 3, Pages: 665-686
Time of Publication: 2012-09
Abstract Various inorganic membranes have demonstrated good capability to separate hydrogen from other gases at elevated temperatures. Hydrogen-permeable, dense, mixed proton-electron conducting ceramic oxides offer superior selectivity and thermal stability, but chemically robust candidates with higher ambipolar protonic and electronic conductivity are needed. In this work, we present for the first time the results of various investigations of La1−xSrxCrO3−∂ membranes for hydrogen production. We aim in particular to elucidate the material’s complex transport properties, involving co-ionic transport of oxide ions and protons, in addition to electron holes. This opens some new possibilities for efficient heat and mass transfer management in the production of hydrogen. Conductivity measurements as a function of pH2 at constant pO2 exhibit changes that reveal a significant hydration and presence of protons. The flux and production of hydrogen have been measured under different chemical gradients. In particular, the effect of water vapor in the feed and permeate gas stream sides was investigated with the aim of quantifying the ratio of hydrogen production by hydrogen flux from feed to permeate and oxygen flux the opposite way (“water splitting”). Deuterium labeling was used to unambiguously prove flux of hydrogen species.
Keywords hydrogen transport membrane; proton permeation; oxygen permeation; water splitting
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CO2 decomposition via oxygen deficient ferrite electrodes using solid oxide electrolyser cell

Source
Time of Publication: 2012-09
Abstract Oxygen Deficient Ferrites (ODF) electrodes integrated with Yttria Stabilized Zirconia (YSZ) electrolyte, electrochemically decompose carbon dioxide (CO2) into carbon (C)/carbon monoxide (CO) and oxygen (O2) in a continuous process. The ODF electrodes can be kept active by applying a small potential bias across the electrodes. CO2 and water (H2O) can also be electrolyzed simultaneously to produce syngas (H2+CO) and O2 continuously that can be fed back to the oxy-fuel combustion. With this approach, CO2 can be transformed into a valuable fuel source allowing CO2 neutral use of the hydrocarbon fuels.
Remark United States Patent Application 20120228150
Link

Transient Oxygen Permeation and Surface Catalytic Properties of Lanthanum Cobaltite Membrane under Oxygen–Methane Gradient

Author Tyler T. Norton and Y. S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 51, Issue: 39, Pages: 12917–12925
Time of Publication: 2012-09
Abstract Oxygen permeation through mixed-conducting ceramic membranes in an air/methane gradient is important for their applications in membrane reactors for air separation and partial oxidation of hydrocarbons. This study examines transient characteristics of oxygen permeation and surface catalytic properties of La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) membranes in an oxygen/methane gradient for an extended period of time. Upon exposure to an oxygen/methane gradient, the oxygen permeation flux of the membrane increases to a maximum at around 55 h, then decreases and reaches a steady-state value at around 200 h. The maximum and steady-state flux is approximately 60% and 30% higher than the initial flux of the fresh membrane, respectively. The surface catalytic properties of the membrane exposed to methane also change with the exposure time in a similar fashion. However, the apparent activation energy for oxygen permeation for the membranes at various stages of the transient study is nearly constant while the effects of temperature, feed pressure, and sweep flow rate on catalytic properties are also similar for the fresh and aged membranes. The surface of a LSCF membrane reacts with methane resulting in a formation of a thin porous layer which changes the surface catalytic properties. The membrane surface becomes more active for reaction with increased selectivity for carbon monoxide formation upon exposure to methane. This lowers oxygen partial pressure in the permeate side and increases the driving force for oxygen permeation and, therefore, increases oxygen permeation flux. Under the studied experimental conditions the membrane can reach steady-state for continuous operation.
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Fabrication, sealing and high pressure testing of tubular La2NiO4+δ membranes for air separation

Authors Paul Inge Dahl, Marie-Laure Fontaine, Florian Ahouanto, Christelle Denonville, Ove Paulsen, Yngve Larring, Thijs Peters, Partow Pakdel Henriksen, Rune Bredesen
Source
Energy Procedia
Volume: 23, Pages: 187–196
Time of Publication: 2012-09
Abstract Recent results achieved on fabrication of La2NiO4+δ membranes, sealing technology and performance in pressurized conditions are presented. Porous tubular membrane supports of up to 1 m length are prepared by ceramic extrusion. Asymmetric La2NiO4+δ membranes are prepared by coating dense selective layers of 10-15 μm thickness onto the porous supports. Glass ceramic seals in the system Na2O-CaO-Al2O3-SiO2 are currently being evaluated for joining the membranes with high temperature steel alloys coated with a corrosion resistance protective layer. By adjusting the composition of the glass system the thermal expansion coefficient is tailored to match that of the membrane and steel material. Good seal adherences towards these materials are obtained. Long term oxygen flux measurements (>4000 hours continuous operation) performed on symmetric (dense) La2NiO4+δ membranes are conducted under various conditions (atmosphere, temperature, pressure). The oxygen flux dependency on the oxygen partial pressure (pO2) is investigated by increasing the feed pressure and oxygen content. An asymptotic flux behavior is observed with increasing pO2. It is seen a significant increase in the flux (by a factor of 6) when increasing the feed pO2 from 0.8 to 2.4 bars while a less significant pO2 dependency is observed with further increase.
Keywords Oxygen transport membranes; fabrication; sealing; pressurized testing
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Effects of the microwave heating on the properties of gadolinium-doped cerium oxide prepared by polyol method

Authors A. Gondolini, E. Mercadelli, A. Sanson, S. Albonetti, L. Doubova, S. Boldrini
Source
Journal of the European Ceramic Society
Volume: 33, Issue: 1, Pages: 67–77
Time of Publication: 2013
Abstract Gadolinium doped ceria (GDC) has received a lot of attention as possible electrolyte material for Intermediate-Temperature (500–800 C) Solid Oxide Fuel Cells (IT-SOFC). Microwave heating has been recently considered in combination with precipitation for the production of oxide or non-oxide nano-powders. In this study, crystalline CeO2 powders doped with different amount of gadolinium were successfully prepared by microwave-assisted polyol method under mild conditions and in one single step. The microwave heating was found to strongly influence the morphological properties of the powder especially for low gadolinium content. IR and thermal analyses helped to identify the major reaction path for the formation of the as-observed complex morphologies. Regardless to the morphology, the powders showed good densification behavior and expected electrochemical properties; Ce0.9Gd0.1O1.95 exhibited the highest conductivity.
Keywords Doped ceria; Microwave processing; Ionic conductivity; Fuel cells; Polyol method
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Investigating Reliability on Fuel Cell Model Identification. Part II: An Estimation Method for Stochastic Parameters

Authors L. Tsikonis, S. Diethelm, H. Seiler, A. Nakajo, J. Van herle, D. Favrat
Source
Fuel Cells
Time of Publication: 2012-08
Abstract An alternative way to process data from polarization measurements for fuel cell model validation is proposed. The method is based on re- and subsampling of I–V data, with which repetitive estimations are obtained for the model parameters. This way statistics such as standard deviations and correlations between the parameters may be experimentally derived. Histograms may also be produced, approximating the probability distributions that they follow. Two experimental case studies are discussed. In the first case, observations are made on the behavior of the parameter values for two mathematical models. As the number of data points (measurement points) employed in the estimation of the parameters increases, parameters with high variances converge to specific values. On the contrary, parameters with small variances diverge linearly. The parameters' histograms do not usually follow normal distributions rather they show a connection between the number of peaks in the graphs and correlations of the parameters. The second case study is an application on a fast degraded SOFC button cell, where the values and the histograms of the parameters are compared before and after degradation.
Keywords Data Fitting; Design of Experiments; Diagnostics; Fast Degradation; Identification; Parameter Estimation; Polarization Curves; Robust Regression; Solid Oxide Fuel cells; Stein's Paradox
Remark DOI: 10.1002/fuce.201200031
Link

Extending the family of oxygen ion conductors isostructural with La2Mo2O9

Authors V.I. Voronkova, E.P. Kharitonova, E.I. Orlova, D.A. Belov
Source
Journal of Solid State Chemistry
Volume: 196, Pages: 45–51
Time of Publication: 2012-12
Abstract X-ray diffraction characterization of materials prepared by solid-state reactions in the ternary systems La2Mo2O9–Nd2W2O9–“Nd2Mo2O9” and La2Mo2O9–Pr2W2O9–Pr2Mo2O9 has shown that, in these systems, compounds isostructural with the oxygen ion conductor La2Mo2O9 exist in wide single-phase regions. Partial tungsten substitution for molybdenum may yield stable Ln2Mo2−2xW2xO9 compounds with the La2Mo2O9 structure, where Ln is a rare-earth element different from lanthanum and praseodymium, e.g., neodymium. Tungsten also stabilizes Pr2Mo2O9, which otherwise decomposes above 700 C. A series of continuous solid solution was found in the La2Mo2O9–Pr2Mo2O9 system. Polymorphism of compounds existing in the above ternary systems was studied by differential scanning calorimetry. The conductivity of most of the compounds studied approaches that of lanthanum molybdate.
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BaTiO3–Bi(Zn1/2Ti1/2)O3–BiScO3 Ceramics for High-Temperature Capacitor Applications

Authors Natthaphon Raengthon, Tutu Sebastian, Denis Cumming, Ian M. Reaney, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 11, Pages: 3554–3561
Time of Publication: 2012-09
Abstract Ceramics based on solid solutions of xBaTiO3–(100−x)(0.5Bi(Zn1/2Ti1/2)O3–0.5BiScO3), where x = 50, 55, and 60 were prepared by solid-state reaction which resulted in a single perovskite phase with pseudocubic symmetry. Dielectric property measurements revealed a high relative permittivity (>1000), which could be modified with the addition of Bi(Zn1/2Ti1/2)O3 (BZT) and BiScO3 (BS) to engineer a temperature-stable dielectric response with a temperature coefficient of permittivity (TCε) as low as −182 ppm/C. By incorporating 2 mol% Ba vacancies into the stoichiometry, the resistivity increased significantly, especially at high temperatures (>200C). Vogel–Fulcher analysis of the permittivity data showed that the materials exhibited freezing of polar nanoregions over the range of 100–150 K. An analysis of optical absorption near the band edge for the Ba-deficient compositions suggested that the enhanced resistivity values were linked to a decrease in the concentration of defect states. An activation energy of ~1.4 eV was obtained from DC resistivity measurements suggesting that an intrinsic conduction mechanism played a major role in the high temperature conductivity. Finally, multilayer capacitors based on these compositions were fabricated, which exhibited dielectric properties comparable to the bulk material. Based on these results, this family of materials has great promise for high-temperature capacitor applications.
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Sr1−xPrxCo0.95Sn0.05O3−δ ceramic as a cathode material for intermediate-temperature solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Hsi-Chuan Lu, Chien-Chung Huang, Chun-Ting Yeh
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 17, Pages: 12548–12556
Time of Publication: 2012-10
Abstract In this study, the physical properties of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics were measured and their potential for use as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs) was evaluated. A cubic phase was retained in all of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics. Analysis of the temperature-dependent conductivity found the SrCo0.95Sn0.05O3−δ and Sr0.9Pr0.1Co0.95Sn0.05O3−δ ceramics exhibiting semiconductor-like behavior below 550 C and metal-like behavior above the same temperature. The Sr0.8Pr0.2Co0.95Sn0.05O3−δ and Sr0.7Pr0.3Co0.95Sn0.05O3−δ ceramics, however, reported a metal-like conductivity in the whole temperature range. The electrical conductivities of the Sr0.8Pr0.2Co0.95Sn0.05O3−δ ceramic at 500 C and 700 C read respectively 1250 S/cm and 680 S/cm, both of which were superior than those in most of the common perovskites. Single cells with a structure of NiO–Sm0.2Ce0.8O2−δ (SDC)/SDC/Sr0.8Pr0.2Co0.95Sn0.05O3−δ-SDC were built and characterized. Addition of SDC in Sr0.8Pr0.2Co0.95Sn0.05O3−δ emerged to be a crucial factor reducing the ohmic resistance (R0) and polarization resistance (RP) of the cell by facilitating a better adhesion to and electrical contact with the electrolyte layer. The R0 and RP of the cell read respectively 0.068 Ω cm2 and 0.0571 Ω cm2 at 700 C and 0.298 Ω cm2 and 1.310 Ω cm2 at 550 C. With no microstructure optimization and hermetic sealing of the cells, maximum power density (MPD) and open circuit voltage (OCV) reached respectively 0.872 W/cm2 and 0.77 V at 700 C and 0.482 W/cm2 and 0.86 V at 550 C. It is evident that Sr1−xPrxCo0.95Sn0.05O3−δ is a promising cathode material for IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
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Nitrogen and hydrogen defect equilibria in Ca12Al14O33: a combined experimental and computational study

Authors Jonathan M. Polfus , Kazuaki Toyoura , Charles H. Hervoches , Martin F. Sunding , Isao Tanaka and Reidar Haugsrud
Source
Journal of Materials Chemistry
Volume: 22, Pages: 15828-15835
Time of Publication: 2012-07
Abstract The defect structure of mayenite is investigated by Density Functional Theory (DFT) defect calculations; in situ electrical conductivity measurements in NH3 atmosphere at high temperature; and X-ray photoelectron spectroscopy (XPS) and gas phase mass spectrometry (GP-MS) of NH3 treated specimens. The computational results suggest that nitrogen is primarily incorporated substitutionally on oxygen sites as NH−2 and N3−. The concentration of nitrogen was estimated to be within the same order of magnitude by XPS, GP-MS and DFT, yielding a stoichiometry close to Ca12Al14O31.5N0.5:(NH2)0.5O0.5 which corresponds well with that obtained by Boysen et al. from similarly treated samples. Out diffusion of nitrogen was found to occur around 700 C in Ar by XPS, GP-MS and conductivity measurements, also in accordance with Boysen et al. The conductivity measurements showed that NH3 treatment had a significant effect on the defect structure of the material which became evident only after replacing the NH3 atmosphere with Ar: the conductivity increased abruptly due to a temporary non-equilibrium reduction of the material as nitrogen diffuses out while the lack of a sufficiently large source of oxygen in the surrounding atmosphere prevents the specimen from re-oxidizing. Further, based on the computational results and the pH2 dependency on conductivity after NH3 treatment, we propose dissolution of hydride ions from H2 in the reduced and highly conductive post-NH3 state.
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Relaxor to Ferroelectric Transitions in (Bi1/2Na1/2)TiO3–Bi(Zn1/2Ti1/2)O3Solid Solutions

Authors Eric A. Patterson, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 11, Pages: 3509–3513
Time of Publication: 2012-11
Abstract Recently, (Bi1/2Na1/2)TiO3 solid solutions have been found to exhibit excellent dielectric and piezoelectric properties. In this study, the dielectric and ferroelectric properties of (1–x)(Bi1/2Na1/2)TiO3–xBi(Zn1/2Ti1/2)O3 (BNT–BZT) solid solutions were investigated. Up to a solubility limit of 8% BZT, distortions to the parent cubic perovskite phase were observed in the diffraction data through splitting of the (001), (011), and (111) reflections. At low concentrations of BZT, the material behaved very much like a conventional ferroelectric, with well-saturated loops with high remanent polarization (Pr ~ 35 μC/cm2). As the BZT content increased, the dielectric behavior displayed characteristics of relaxor behavior. Polarization hysteresis data at elevated temperatures and a thermal hysteresis in the dielectric maximum were evidence for a relaxor to ferroelectric transition.
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Fabrication, structural and electrical characterization of Lanthanum Tungstate films by Pulsed Laser Deposition

Authors Einar Vollestad, Agnieszka Gorzkowska-Sobas, Reidar Haugsrud
Source
Thin Solid Films
Volume: 520, Issue: 21, Pages: 6531–6534
Time of Publication: 2012-08
Abstract Films of lanthanum tungstate, 3 μm in thickness, were fabricated by means of Pulsed Laser Deposition on a Pd foil. The films were characterized by X-ray diffraction, scanning electron microscopy, X-ray Photoelectron Spectroscopy and their electrical conductivity was measured at temperatures between 400 and 800 C in different gas atmospheres. The films’ structure and electrical characteristics are close to what is reported in the literature for corresponding polycrystalline material. The films exhibit fairly high proton conductivity at elevated temperatures, which make them interesting for components in hydrogen-related technologies. Changes in microstructure and the crystallographic orientation observed at higher temperatures were accompanied by changes in the conductivity characteristics.
Keywords Proton conducting oxide; ceramics; Hydrogen transport membrane; Films by Pulsed Laser Deposition; ionic conductor; lanthanum tungstate; La6WO12
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Nd-doped Ba(Ce,Zr)O3 − δ proton conductors for application in conversion of CO2 into liquid fuels

Authors Wojciech Zając , Emil Hanc, Agnieszka Gorzkowska-Sobas, Konrad Świerczek, Janina Molenda
Source
Solid State Ionics
Volume: 225, Pages: 297–303
Time of Publication: 2012-10
Abstract The paper presents crystal structure, transport properties, chemical stability in CO2 atmosphere and thin film membrane preparation for materials from the Ba(Ce1 − xZrx)0.9Nd0.1O2.95 (x = 0, 0.25, 0.5, 0.75, 1) group of perovskite-type structure oxides. Transformation of crystal structure from orthorhombic Pnma to orthorhombic Imma and cubic with increasing xZr was observed along with linear decrease of pseudo-cubic unit cell volume and free lattice volume. Electrical conductivity of bulk and grain boundary was determined in dry air, as well as in air humidified with H2O or D2O. The highest proton conductivity was observed for material with xZr = 0.25. Further increase of Zr content led to decrease of conductivity as high as 2 orders of magnitude. This effect was coupled with bell-shape dependence of activation energy and pre-exponential term. Such behavior was explained as superimposed effects of high proton mobility for zirconium-rich materials due to cubic symmetry and cerium-rich materials due to softness of oxygen–oxygen separation distance, along with high proton concentration for cerium-rich perovskites. The deteriorating effect of grain boundaries on total electrical conductivity was far more pronounced for Zr-rich materials than in the case of Ce-rich ones. Declining grain boundary conductivity was attributed to both increase of number of grain boundaries and decrease of inherent grain boundary conductivity for Zr-rich samples. The highest chemical stability in CO2 atmosphere was achieved for high-Zr content materials, on the contrary, for BaCe0.9Nd0.1O2.95 in CO2 atmosphere, the decomposition onset temperature was below 500 C. 2 μm thin film membrane of Ba(Ce0.75Zr0.25)0.9Nd0.1O2.95 was successfully prepared on c-plane sapphire and fused silica substrates. Film's crystal structure matched that of the bulk material. The electrical conductivity of thermally treated film obtained on c-plane sapphire in wet air was 3.7 10− 4 S cm− 1 at 600 C.
Keywords Proton conductors; BaCeO3–BaZrO3 solid solutions; Isotope effect; Grain boundary effect; Thin films
Remark Link

High Curie temperature ternary piezoelectric ceramics

Authors Tan, Xiaoli (Ames, IA, US) Hu, Wei (Ames, IA, US)
Source
Time of Publication: 2012-06
Abstract A preferred piezoelectric ceramic material is a BiFeO3—PbZrO3—PbTiO3 ternary solid solution wherein proportions of the constituent perovskite metal oxides are selected so that the material exhibits relatively high Curie temperatures above 380 C. and useful piezoelectric properties.
Remark United States Patent Application 20120145943
Link

Hydrogen permeation, transport properties and microstructure of Ca-doped LaNbO4 and LaNb3O9 composites

Authors Wen Xing, Guttorm E. Syvertsen, Tor Grande, Zuoan Li, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 415-416, Pages: 878–885
Time of Publication: 2012-10
Abstract Two composites consisting of the proton conducting Ca-doped LaNbO4 and electron conducting LaNb3O9 with respectively 90 and 70 vol% LaNbO4 were prepared by spark plasma sintering. The amount of hydrogen produced at the sweep side was measured as a function of temperature and pH2 gradient under wet and dry sweep gas conditions. The hydrogen flux increases with increasing temperature and feed-sidepH2. The flux is significantly higher for the 70 vol% LaNbO4 composite than the 90 vol% LaNbO4 composite. Ambipolar conductivities calculated from the flux data showed the same pH2 dependence for both composites. The electrical conductivity of the 70 vol% LaNbO4 composite was characterized as a function of temperature under wet hydrogen. The microstructure and phase distribution of the two composites are analyzed and their transport properties with different flux limiting processes are discussed. An increased hydrogen production with wet compared to dry sweep gas is concluded to reflect water splitting due to transport of oxygen from the permeate to the feed side.
Keywords Hydrogen flux; Proton conductivity; Ceramic-ceramic composite; LaNbO4; LaNb3O9; Ambipolar conductivity; Water splitting
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A novel coulometric titration setup—Principals, design and leakage minimization

Authors Mehdi Pishahang, Egil Bakken, Svein Stlen
Source
Thermochimica Acta
Time of Publication: 2012-05
Abstract This article presents a new coulometric titration setup and describes the principles of operation, the main precautions to be taken into account to reduce the systematic errors, and evaluates the working range and the accuracy of the measurements. The major source of error, the oxygen leakage, is studied in detail and modeled based on leakage of oxygen through the YSZ solid electrolyte. Decreasing the difference in chemical potential of oxygen between inside and outside of the cell is studied as an applied measure to decrease the oxygen leakage. Flushing the pumping solid electrolyte by N2 shows a reasonable improvement. Eventually, oxygen non-stoichiometry of SrFeO3−δ is measured at 1273 K in the oxygen partial pressure range of 0.6 < −log(pO2/atm) < 12. The resulting values are in good agreement with the literature.
Keywords Coulometric titration; Oxygen non-stoichiometry; Oxygen leakage

High Power Plasma Sprayed Intermediate Temperature Solid Oxide Fuel Cells with Sm0.5Sr0.5CoO3-δ Cathode

Authors Chang-sing Hwang , Chun-Huang Tsai, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Procedia Engineering
Volume: 36, Pages: 81–87
Time of Publication: 2012-05
Abstract The cells with porous Ni/Fe(∼10 wt%) metal plate as a supporting substrate, double layers of La0.75Sr0.25Cr0.5Mn0.5 O3-δ (LSCM) and nanostructured Ce0.55La0.45O2-δ/Ni (LDC/Ni) as an anode, LDC as an anode interlayer, La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as an electrolyte, LSGM/Sm0.5Sr0.5CoO3-δ (SSC) as a cathode interlayer and SSC as a cathode current collector, were prepared by atmospheric plasma spraying (APS) coating processes followed by a heating treatment. The current-voltage-power and AC impedance measurement results show that the prepared cell heat-treated at 850 C for 3 hours in air with a dead load of 1000 g cm-2 has an attracting performance. The measured maximum output power densities of this cell have reached 0.777, 0.742, 0.659, 0.542, 0.393, and 0.250 W cm-2 at 800, 750, 700, 650, 600, and 550 C respectively. The measured ohmic and polarization resistances are 0.241, 0.254, 0.282, 0.328, 0.42, 0.62 and 0.055, 0.064, 0.083, 0.128, 0.23, 0.471 Ω cm2 at 800, 750, 700, 650, 600, and 550 C respectively. After correction of the resistance inside the ProboStat system, the predicted actual maximum power densities that a cell can deliver are 1.95, 1.613, 1.186, 0.823, 0.512, and 0.293 W cm-2 at 800, 750, 700, 650, 600, and 550 C respectively.
Keywords Atmospheric plasma spray; solid oxide fuel cells; metal-supported; nanostructured; Sm0.5Sr0.5CoO3-δ
Remark Link

Electromechanical strain in Bi(Zn1/2Ti1/2)O3–(Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 solid solutions

Authors Eric A. Patterson, David P. Cann, Jan Pokorny, and Ian M. Reaney
Source
Journal of Applied Physics
Volume: 111, Issue: 9 Time of Publication: 2012-05
Abstract Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O3–(Bi0.5K0.5)TiO3–(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing Tmax of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT–40BKT–57.5BNT, a secondary transition commonly observed for morphotropic phase boundary (MPB) BNT–BKT was observed. The ferroelectric behavior of the system was characterized by a transition where the polarization hysteresis showed a severe pinching effect on remanent polarization (20.8 μC/cm2 at 2.5% BZT) as BZT contents was increased (Pr = 2.3 μC/cm2 at 20% BZT). Similarly, as the temperature increased to 175 C, the remanent polarization of the 2.5% BZT composition significantly reduced to 2.1 μC/cm2. The onset of this transition corresponds to the lower temperature frequency dispersion observed in the dielectric spectrum. The strain hysteresis experienced analogous transition to the polarization, with a change in shape from typical ferroelectric butterfly to a complete loss of negative strain as BZT concentration increased. Maximum strain values of 0.33% were observed at 5-40-55 accompanied by a large d33* = 547pm/V.
Remark Published online 10 May 2012
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Process and Apparatus of CO2 Energy Source Adopted in Solid Oxide Fuel Cell - CO2 Energy Conversion Cycle

Authors M. Lee, C. Wang, Y. Chang, W. Kao, T. Lin, J. Chang, R. Yang, L. Lee
Source
Time of Publication: 2012-05
Abstract A process and apparatus of “Solid Oxide Fuel Cell (SOFC)-CO2 Energy Conversion Cycle (referred to as SOFC-CO2-ECC)” are invented to adopt CO2 as energy sources from waste/stock gas or convert and fix it in the useful compounds. CO2 is converted into CO and O2 via simultaneously catalytic and electrochemical reactions in SOFC for power generation and CO2 cracking. Furthermore, CO is used either as the fuel in SOFC for power generation or starting materials in the chemical reactors to produce CO-derivatives of energy source materials and useful chemical compounds. Hence, SOFC-CO2-ECC is an active or scientific carbon cycle with zero emission of CO2. Thus, the efficacy of environmental protection via solving the problem of CO2 greenhouse effect is achieved, so as to grasp of the “Right of Carbon Emission Trading” issues.
Remark United States Patent Application 20120115067
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Effect of doped ceria interlayer on cathode performance of the electrochemical cell using proton conducting oxide

Authors T. Sakai , S. Matsushita, J. Hyodo, Y. Okuyama, M. Matsuka, T. Ishihara, H. Matsumoto
Source
Electrochimica Acta
Volume: 75, Pages: 179–184
Time of Publication: 2012-07
Abstract Introduction of doped ceria interlayer to cathode/electrolyte interface of the electrochemical cell with proton conducting electrolyte was investigated using thin Ce0.8Yb0.2O2−δ (YbDC) interlayer of about 500 nm thickness. YbDC interlayer conducted a large amount of protons as much as 170 mA cm−2. It was also found that cathode overpotential of the YbDC interlayer cells consistently showed a plateau at about 400 mV, at which that of the non-interlayer cells did not show, suggesting a possibility that cathode reaction is changed by introducing the doped ceria interlayer. This result also indicates that the interlayer showed high activity for cathode reaction when enough cathodic bias was applied. Especially, the interlayer showed high activity for the improvement of poor cathode reaction between SrZr0.9Y0.1O3−α (SZY-91) electrolyte and platinum cathode.
Keywords Proton conduction; Doped ceria; Cathode interlayer; Electrochemical steam electrolysis
Remark Available online 4 May 2012
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Polymorphism and Oxide Ion Migration Pathways in Fluorite-Type Bismuth Vanadate, Bi46V8O89

Authors Xiaojun Kuang, Julia L. Payne, James D. Farrell, Mark R. Johnson, and Ivana Radosavljevic Evans
Source
Chem. Mater.
Volume: 24, Issue: 11, Pages: 2162–2167
Time of Publication: 2012-05
Abstract We report the synthesis, structural characterization, and ionic conductivity measurements for a new polymorph of bismuth vanadate Bi46V8O89, and an ab initio molecular dynamics study of this oxide ion conductor. Structure determination was carried out using synchrotron powder X-ray and neutron diffraction data; it was found that β-Bi46V8O89 crystallizes in space group C2/m and that the key differences between this and the previously reported α-form are the distribution of Bi and V cations and the arrangement of the VO4 coordination polyhedra in structure. β-Bi46V8O89 exhibits good oxide ion conductivity, with σ = 0.01–0.1 S/cm between 600 and 850 C, which is about an order of magnitude higher than yttria stabilized zirconia. The ab initio molecular dynamics simulations suggest that the ion migration pathways include vacancy diffusion through the Bi–O sublattice, as well as the O2– exchanges between the Bi–O and the V–O sublattices, facilitated by the variability of the vanadium coordination environment and the rotational freedom of the VOx coordination polyhedra.
Keywords Oxide ion conductors; bismuth vanadates; X-ray and neutron diffraction; AIMD simulations
Remark Publication Date (Web): May 3, 2012
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