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Ion mobility, phase transitions, and conductivity of crystal phases in KF-CsF-SbF3-H2O system according to data of NMR and impedance spectroscopy

Authors V. Ya. Kavun, L. A. Zemnukhova, A. I. Ryabov, A. B. Podgorbunskii, S. V. Gnedenkov, S. L. Sinebryukhov and V. I. Sergienko
Source
Russian Journal of Electrochemistry
Volume: 48, Issue: 1, Pages: 104-110
Time of Publication: 2012-01
Abstract The methods of NMR, thermogravimetric analysis, and impedance spectroscopy were used to study ion mobility, phase transitions, and ion conductivity in crystal phases in the KF-CsF-SbF3-H2O system. Analysis of 19F NMR spectra allowed tracing the dynamics of ion movement in the fluoride sublattice under temperature variations, determining their types and temperature ranges, in which they are implemented. The observed phase transitions in potassium-cesium fluoroantimonates(III) are phase transitions to the superionic state. It is found that the predominant form of ion movement in the high-temperature modifications formed as a result of phase transitions becomes diffusion of fluoride ions. According to the results of electrophysical studies the K1−xCsx SbF4 (x ≤ 0.2) high-temperature phases are superionic. Their conductivity reaches the values of ∼10−2 to 10−3 S/cm at 463–483 K. The high-temperature phases are stabilized under cooling, which results in a significant increase in conductivity at the room temperature.
Keywords potassium-cesium tetrafluoroantimonates(III) – ion mobility – phase transitions – conductivity – NMR spectra
Remark DOI: 10.1134/S1023193512010090
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Defect structure and its nomenclature for mixed conducting lanthanum tungstates La28–xW4+xO54+3x/2

Authors Skjalg Erdal, Liv-Elisif Kalland, Ragnhild Hancke, Jonathan Polfus, Reidar Haugsrud, Truls Norby, Anna Magrasˇ
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8051–8055
Time of Publication: 2012-05
Abstract Based on results from experimental and theoretical studies of the crystal structure of lanthanumtungstateView the MathML source, we present a defect model comprising an inherently disordered and partially occupied oxide ion sublattice, which rationalizes hydration and ionic conduction of the materials in the undoped state. Applying the model to experimental conductivity data enables extraction of defect thermodynamics and transport parameters of protons, oxide ions and electronic defects. The standard enthalpy and entropy changes of the hydration of inherent oxygen vacancies are estimated to be −83 kJ/mol and −125 J/mol K (per mole of H2O), respectively.
Keywords Lanthanum tungstate; Defect structure; Inherent disorder; Partial occupancy; Mixed conductor
Remark Link

The role of B-site cations on proton conductivity in double perovskite oxides La2MgTiO6 and La2MgZrO6

Authors Camilla K. Vigen, Tor Svendsen Bj°rheim, Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7983–7994
Time of Publication: 2012-05
Abstract Acceptor-doped La2MgTiO6 (LMTO) and La2MgZrO6 (LMZO) have been investigated to contribute to clarify the role of the B-site cations in A2B′B″O6 double perovskite oxides on formation and mobility of protons. Thermogravimetry and a.c. conductivity measurements in the temperature range 1000-300 ░C, as well as DFT-calculations of LMTO, have been the basis for evaluating hydration thermodynamics and transport parameters of the materials. Both compounds show exothermic hydration of oxygen vacancies, but low concentrations of protons. The proton transport is limited by relatively high activation energies of mobility; 0.84 eV and 0.78 eV for LMTO and LMZO, respectively. This is suggested to reflect association to effectively negative charged defects formed by site exchange among the B-site cations. Consequently, the maximum proton conductivity of LMTO and LMZO is in the order of 10−5 S/cm.
Keywords Double perovskite; La2MgTiO6; La2MgZrO6; Proton mobility; Hydration thermodynamics
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Influence of Microwave-Assisted Pechini Method on La0.80Sr0.20Ga0.83Mg0.17O3–δ Ionic Conductivity

Authors S. Boldrini, C. Mortal˛, S. Fasolin, F. Agresti, L. Doubova, M. Fabrizio, and S. Barison
Source
Fuel Cells
Volume: 12, Issue: 1, Pages: 54–60
Time of Publication: 2012-02
Abstract With the aim of investigating the microwave influence on the electrolyte material properties, La0.80Sr0.20Ga0.83Mg0.17O2.815 was prepared by both a conventional and a microwave-assisted sol–gel Pechini method. With respect to the conventional Pechini method (hereafter SGP), the microwave assisted process (hereafter MWA-SGP) guaranteed a faster procedure, reducing the time needed to remove the excess solvents to complete the polyesterification reaction from some days to a few hours. In fact, when a MWA-SGP method was used, powders having higher phase purity were obtained. The sintering process at 1,450 ░C of the powders prepared by both methods yielded pellets with similar density values (≥92% of theoretical). Nevertheless, only by microwave-assisted process single-phase products were obtained and no secondary phases such as tetragonal LaSrGaO4 and LaSrGa3O7 were detected. These by-products have been demonstrated to be detrimental for conductivity. Indeed, pellets obtained by MWA-SGP method showed oxygen ionic conductivity values higher (about 30–40%) than those checked for SGP samples, thus demonstrating the important role of the microwave process on reducing time and costs and on improving the electrolyte properties.
Keywords Ionic Conductivity;IT-SOFC;Microwave Processing;(Sr, Mg)-Doped LaGaO3;Sol–Gel
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Impact of Parylene-A Encapsulation on ZnO Nanobridge Sensors and Sensitivity Enhancement via Continuous Ultraviolet Illumination

Authors C.-C. Huang, A.D. Mason, J.F. Conley, C. Heist, M.T. Koesdjojo, V.T. Remcho and T. Afentakis
Source
Journal of Electronic Materials
Volume: 41, Issue: 5, Pages: 873-880
Time of Publication: 2012-05
Abstract The impact of parylene-A encapsulation and the effect of continuous ultraviolet (UV) exposure on ZnO nanobridge sensor response are investigated. ZnO nanowire (NW) devices are fabricated using a novel method that involves selective growth of ZnO nanobridges between lithographically defined pads of carbonized photoresist (C-PR). We find that a thin coating of parylene-A effectively attenuates the response of NW devices to O2, H2O vapor, and UV illumination. The accessibility of the amine group on parylene-A for chemical functionalization is verified by transforming the amine groups on the surface of the parylene-A coating into aromatic imine groups, followed by UV–Vis absorption. Our results suggest that, in addition to modulating environmental sensitivity and providing protection of the ZnO NWs for liquid- and vapor-phase sensing, the parylene-A encapsulation may also serve as an activation layer for further specific functionalization targeting selective sensing. We also found that the sensitivity and response time of ZnO nanobridge devices to O2 are dramatically improved by continuously exposing the nanobridge devices to UV illumination. Finally, we show that the C-PR directed growth method can also be used to isolate free-standing NW carpet.
Keywords ZnO – nanowire – parylene – CVD – nanobridge – sensor – functionalization – directed integration
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On the hydration of grain boundaries and bulk of proton conducting BaZr0.7Pr0.2Y0.1O3-δ

Authors Kristine Bakkemo Kost°l, Anna Magrasˇ, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7970–7974
Time of Publication: 2011-12
Abstract We report here for the first time bulk and grain boundary conductivities from impedance spectra of a ceramic proton conductor (BaZr0.7Pr0.2Y0.1O3-δ) taken during hydration and H/D isotope exchange transients (at 400 ░C). The results suggest that water moves quickly along grain boundary cores, and then interact from there with the space charge layers and, in turn, grain interiors. Hydration and H/D isotope exchange have simple monotonic effects on the bulk conductivity in line with what is expected from it being dominated by protons. The transients for grain boundary conductivity exhibit however hysteresis: During hydration, the core charge and grain boundary resistance appear to go through transient minima related to non-equilibrium distributions of defects between the core and grain interior – notably because protons diffuse faster than oxygen vacancies between the grain boundary and grain interior. At equilibrium, hydration increases the core charge and the depletion of positive charge carriers in the space charge layers. During H/D isotope exchange relatively fast hysteretic transients indicate that the space charge layers experience changes in charge carrier (D+ vs. H+) mobility as well as in D2O vs. H2O hydration thermodynamics.
Keywords BaZrO3, Pr-substituted, acceptor-doped; BaZr0.7Pr0.2Y0.1O3-δ; Proton conductivity; Grain boundaries, space charge layer; Hydration; Impedance spectroscopy
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Synthesis, structural and electrical properties of double perovskite Sr2NiMoO6 ceramics

Authors A. Prasatkhetragarn, S. Kaowphong and R. Yimnirun
Source
Applied Physics A: Materials Science & Processing
Volume: 107, Issue: 1, Pages: 117-121
Time of Publication: 2012-01
Abstract The double perovskite Sr2NiMoO6 powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained when calcined in air at 1300░C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric properties (ε r and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280░C for conventional route, while no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different starting processes affected the phase formation behavior and the electrical properties of Sr2NiMoO6 ceramics.
Remark Link

Dielectric Relaxation in BaTiO3–Bi(Zn1/2Ti1/2)O3 Ceramics

Authors Natthaphon Raengthon, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 5, Pages: 1604–1612
Time of Publication: 2012-05
Abstract A dramatic improvement in the dielectric and electrical properties has been observed in ceramics of 0.8BaTiO3–0.2Bi(Zn1/2Ti1/2)O3 through the introduction of Ba vacancies. It possesses a high relative permittivity (εr > 1150) along with a low dielectric loss (tan δ < 0.05) that is maintained up to temperatures as high as 460░C. It is also characterized by a high resistivity of 70 GΩ-cm, which remains constant up to 270░C. Analysis of complex impedance (Z*) and complex electric modulus (M*) data, measured over the frequency range of 1–106 Hz, revealed a number of important findings. At high temperatures (T > 255░C), a complex plane analysis of Z″ versus Z′ and the frequency dependence of Z″ suggests an electrically inhomogeneous microstructure for the stoichiometric composition. The stoichiometric composition exhibited activation energies of ~1 eV which suggests an extrinsic conduction mechanism. However, the introduction of Ba vacancies resulted in electrically homogeneous microstructure. An overlap of the Z″ and M″ peaks in the frequency domain and much larger activation energies were observed, on the order of half of the band gap, suggesting an intrinsic conduction mechanism. A more detailed analysis of the data reveals insights into the physical mechanisms underpinning the dielectric and ac conductivity.
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Fabrication and electrochemical properties of cathode-supported solid oxide fuel cells via slurry spin coating

Authors Min Chen, Jing-Li Luo, Karl T. Chuang, Alan R. Sanger
Source
Electrochimica Acta
Volume: 63, Pages: 277–286
Time of Publication: 2012-02
Abstract A cathode-supported SOFC consisting of LSM (La0.8Sr0.2MnO3-δ) cathode supporter, LSM-Sm0.2Ce0.8O2-δ (SDC) cathode functional layer (CFL), yttria stabilized zirconia (YSZ)/SDC bi-layered electrolyte and Ni-YSZ anode layer was fabricated by a slurry spin coating technique. The influence of the porosity in both the CFL and cathode supporter on the electrochemical properties of the cells has been investigated. It was found that properly controlling the porosity in the CFL would improve the performance of the cells using O2 in the cathode side (O2-cells), with a maximum power density (MPD) value achieving as high as 0.58 W•cm−2 at 850 ░C. However, this improvement is not so evident for the cells using air in the cathode side (air-cells). When increasing the porosity in the cathode-supporter, a significant increase of the power density for the air cells due to the decreasing Rconc,c(concentration polarization to the cell resistance) can be ascertained. In terms of our analysis on various electrochemical parameters, the Ract (activation polarization to the cell resistance) is assumed to be mainly responsible for the impedance arcs measured under the OCV condition, with a negligible Rconc,cvalue being able to be detected in our impedances. In this case, a significant decreasing size of the impedance arcs due to the increasing porosity in the cathode supporter would correspond to a decrease of the Ract values, which was proved to be induced by the decreasingRconc,c.
Keywords Slurry spin coating; Cathode-supported SOFC; Concentration polarization; Activation polarization; Power density
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The effect of cation non-stoichiometry in LaNbO4 materials

Authors Guttorm E. Syvertsen, Anna Magrasˇ, Reidar Haugsrud, Mari-Ann Einarsrud, Tor Grande
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8017–8026
Time of Publication: 2012-05
Abstract The effect of cation non-stoichiometry in LaNbO4 was investigated by impregnating nano-crystalline LaNbO4 with small amounts of La3+, Nb5+ and Ca2+ oxide precursors. The sintering properties of the modified LaNbO4 powders were investigated by dilatometry, and the microstructure and phase composition were studied by electron microscopy and X-ray diffraction. The electrical properties of the materials were studied by 4-point DC-conductivity and 2-point 4-wire AC-conductivity at elevated temperatures in controlled atmosphere. Minor variations in the cation stoichiometry were shown to have a pronounced effect on both the sintering properties as well as the electrical conductivity. Addition of CaO, which introduced secondary phases above 0.25 mol% CaO, increased the sintering temperature and improved the conductivity of the materials. La2O3- and Nb2O5-excess materials did not show large variation in the electrical conductivity relative to pure LaNbO4, while the sintering properties were strongly affected by the nominal La/Nb ratio in LaNbO4. The present findings demonstrate the sensitivity of cation non-stoichiometry in materials with limited solid solubility.
Keywords LaNbO4; Proton conductivity; Phase purity; Solid solubility
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Effects of surface coatings on the determination of Dchem and kchem in La2NiO4+δ by conductivity relaxation

Authors Zuoan Li, Reidar Haugsrud
Source
Solid State Ionics
Volume: 206, Pages: 67-71
Time of Publication: 2012-01
Abstract In this work, we utilize surface modification to accurately determine oxygen diffusivity and surface exchange in La2NiO4 + δ by transient conductivity. To achieve ‘instantaneous’ gas exchange in the reaction cell, a total pressure change was adopted instead of exchange of gas mixtures at 1 atm. Conductivity relaxation measurements were performed in the temperature range of 600–900 ░C and at oxygen partial pressures of 0.2, 1.0 and 1.9 atm. Due to the large uncertainties associated with deriving oxygen chemical diffusion and surface coefficients simultaneously, we limited the relaxation to pure bulk diffusion control by coating nano-grained La2NiO4 + δ particles on the sample surface. After determining Dchem, kchem was derived by fitting the relaxation data of the uncoated sample. The transient experiments via both oxidation (a step change of pO2 from 0.2 to 1.0 atm) and reduction (1.9 to 1.0 atm) give consistent results of Dchem and kchem showing Arrhenius-type behaviour with activation energies of ~ 90 kJ/mol and ~ 150 kJ/mol, respectively.
Keywords Conductivity relaxation; Surface modification; Surface exchange; Oxygen diffusion; La2NiO4 + δ
Remark Link

Hydration and proton conductivity in LaAsO4

Authors Tor S. Bj°rheim, Truls Norby and Reidar Haugsrud
Source
Journal of Materials Chemistry
Volume: 22, Issue: 4, Pages: 1652-1661
Time of Publication: 2012-04
Abstract Incorporation and transport of protonic defects have been studied in nominally undoped and 1 and 3 mol% Sr-doped LaAsO4 prepared by a co-precipitation route. AC impedance of the materials was measured as a function of temperature (1150 to 400 ░C), pO2 (1 to 1 Î 10−5 atm) and pH2O (0.025 to 3 Î 10−5 atm). The bulk conductivities generally decrease with decreasing temperature and moreover with decreasing pH2O within the whole temperature range. At the highest temperatures, a small decrease in the conductivity with decreasing pO2 was also observed. The defect structure of Sr-doped LaAsO4 appears to be dominated by oxygen vacancies in the form of pyroarsenate ions, As2O4−7, in dry atmospheres at high temperatures and by protonic defects in the form of hydrogen arsenate ions, HAsO2−4, in wet atmospheres. A significant isotope effect shows that protons contribute to the total conductivity at all temperatures under wet conditions and predominate at temperatures below [similar]850 ░C. The remaining contributions are attributed to oxide ions and electron holes. The extracted hydration thermodynamics are comparable to those determined for other LnXO4 (X = P, V, Nb, Ta) compounds, and the enthalpy of mobility of protons (86 ▒ 5 and 88 ▒ 5 kJ mol−1 for the 1 and 3 mol% doped samples, respectively) follows an apparent trend for the isostructural LaXO4 (X = P, As, V) series with the enthalpy of mobility of protons decreasing with increasing radius of the X-site cation. However, the partial proton conductivities of Sr-doped LaAsO4 are lower than those determined for acceptor doped LaPO4 and LaVO4 for which the possible reasons are discussed.
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Evaluation of the electrode/electrolyte contact quality in solid oxide fuel cells

Authors Jacqueline Amanda Figueiredo dos Santos, Michel Kleitz, Tulio Matencio, Rosana Zacarias Domingues
Source
Electrochimica Acta
Volume: 60, Pages: 224–229
Time of Publication: 2012-01
Abstract Symmetrical cells have been prepared by depositing suspensions with different active powder concentrations (50% and 60% by weight respectively) of lanthanum strontium cobalt iron oxide (La0.6Sr0.4Co0.2Fe0.8O3-δ) on identical yttria stabilized zirconia pellets (LSCF/YSZ/LSCF). Their impedance characteristics are compared to that of a symmetrical cell with platinum electrodes deposited on a similar zirconia pellet (Pt/YSZ/Pt). The LSCF cells show different values of the electrolyte resistance. Referring to the electrolyte resistance obtained with the Pt cell and assuming that this value corresponds to almost perfect electrode/electrolyte contacts, it is possible to estimate the Effective Conducting Area (ECA) of the electrodes. The use of the ECA parameter allows a better comparison of the electrode polarizations.
Keywords solid oxide fuel cells; porous electrodes; cathode
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Influence of Pr substitution on defects, transport, and grain boundary properties of acceptor-doped BaZrO3

Authors Anna Magrasˇ, Christian Kj°lseth, Reidar Haugsrud, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7962–7969
Time of Publication: 2012-05
Abstract We report on effects of partially substituting Zr with the multivalent Pr on the conductivity characteristics of acceptor (Gd) doped BaZrO3-based materials. BaZr0.6Pr0.3Gd0.1O3−δ was sintered 96% dense at 1550 ░C with grains of 1–4 μm. The electrical conductivity was characterised by impedance spectroscopy and EMF transport number measurements as a function of temperature and the partial pressures of oxygen and water vapour. H2O/D2O exchanges were applied to further verify proton conduction. The material is mainly a mixed proton–electron conductor: the p-type electronic conductivity is ∼0.004 and ∼0.05 S/cm in wet O2 at 500 and 900 ░C, respectively, while the protonic conductivity is ∼10−4 S/cm and ∼10−3 S/cm. The material is expectedly a pure proton conductor at sufficiently low temperatures and wet conditions. The specific grain boundary conductivity is essentially equal for the material with or without Pr, but the overall resistance is significantly lower for the former. We propose that replacing Pr on the Zr site reduces the grain boundary contribution due to an increased grain size after otherwise equal sintering conditions.
Keywords BaZrO3; BaPrO3; Defects and transport; Grain boundaries; Grain boundary specific conductivity
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Effects of A and B site acceptor doping on hydration and proton mobility of LaNbO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8004–8016
Time of Publication: 2012-05
Abstract Acceptor doping of the high temperature proton conductor LaNbO4 has been studied by impedance spectroscopy in various atmospheres at 300–1100 ░C and by X-ray powder diffraction and scanning electron microscopy. Doping LaNbO4 on both A and B site (with Ca and Ti, respectively) resulted in a two-phase composition of LaNbO4 and LaNb3O9. This composite is interesting as the two phases make it a mixed proton and electron conductor. The electrical characterisation of Ti-doped LaNbO4 revealed mixed electronic (n- and p-type) and ionic conductivity at temperatures above approx. 750 ░C, while proton conductivity was dominating below this temperature under wet conditions. Ti-doping resulted in higher activation enthalpy and lower mobility of protons as compared to Ca-doping, attributed to stronger proton–acceptor association in the former case. Thermodynamic constants for hydration of associated protons and proton–acceptor association as well as mobility parameters were fitted to the experimental data and came out as , , , and , and . Neither B site doping nor A and B site co-doping showed indications of increased solubility relative to sole A site doping in LaNbO4.
Keywords LaNbO4; Ti-doped LaNbO4; Defect association; Proton mobility; Proton conductivity; Hydration thermodynamics
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Effects of (LaSr)(CoFeCu)O3-δ Cathodes on the Characteristics of Intermediate Temperature Solid Oxide Fuel Cells

Authors Sea-Fue Wang, Chun-Ting Yeh, Yuh-Ruey Wang, Yung-Fu Hsu
Source
Journal of Power Sources
Volume: 201, Pages: 18–25
Time of Publication: 2012-03
Abstract In this study, Cu2+ ions doped La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes are prepared for use in solid oxide fuel cells (SOFCs). The maximum electrical conductivities of the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ (438 S cm−1) and the La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ (340 S cm−1) discs are higher than that of the La0.6Sr0.4Co0.2Fe0.8O3−δ disc (LSCF; 81 S cm−1) sintered at 1100 ░C. The substitution of Cu2+ over Fe3+ leads to a higher coefficients of thermal expansion (CTE), while the replacement of Co3+ by Cu2+ results in a lower CTE. Single cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 650 ░C and 550 ░C show similar ohmic resistance (R0) values while the polarization resistance (RP) values of the cells with the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ and a0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes are slightly lower than that of the single cell with the La0.6Sr0.4Co0.2Fe0.8O3−δ cathode, indicating that the Cu2+-doped LSCF cathode exhibits a greater electrochemical catalytic activity for oxygen reduction. Maximum power densities of the cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 700 ░C read respectively 1.07, 1.15, and 1.24 W cm−2. It is evident that the doping of Cu2+ ions in LSCF is beneficial to the electrochemical performance of the cells.
Keywords Solid oxide fuel cell; cathode; cathode; impedance; Cell performance
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Synthesis and Enhanced Proton Conduction in a 20 mol% Ytterbium Doped Barium Zirconate Ceramic Using Zn as Sintering Aid

Authors Seikh M.H. Rahman, Istaq Ahmed, Sten G. Eriksson
Source
Applied Mechanics and Materials
Mechanical and Aerospace Engineering
Volume: 110-116 Time of Publication: 2011-10
Abstract 20% Ytterbium (III)-doped perovskite structured barium zirconate, BaZrO3, was prepared by two different synthesis routes: solid state and sol-gel routes. 2 % Zinc (II) was added as an acceptor dopant at the Zr (IV) site according to stoichiometry. It was also added as 2 % excess of the formula. The purpose of this study is to see how zinc (II) acts as a sintering aid in view of synthesis route, densification and conductivity of the material. A dense ceramic (90% of theoretical density) was achieved by the sol-gel method when stoichiometry was adjusted. Phase purity of the samples was checked by X-ray powder diffraction (XRD). Thermogravimetric analysis (TGA) and Impedance spectroscopy (IS) was used to characterize hydration and electrical conductivity respectively.The data shows that the addition of stoichiometric amounts of Zn2+ via sol-gel synthesis route promotes not only densification but also water incorporation and conductivity in comparison with the solid state route, keeping the same final sintering temperature of 1500░C. For example, pre-hydrated BaZr0.78Zn0.02Yb0.2O3-δ, prepared via the sol-gel method shows total conductivity (σtot) value of 3.14*10-5 and 3.8*10-3 Scm-1, whereas for the solid state route, σtot values are 1.74*10-5 and 8.87*10-4 Scm-1 under dry Ar (heating cycle) at 300░ C and 600░ C, respectively.
Keywords BaZrO3, Impedance Spectroscopy, Proton Conductivity, Sintering Aid, TGA, X-Ray Diffraction (XRD)
Editor Wu Fan
Remark Online since October, 2011; DOI 10.4028/www.scientific.net/AMM.110-116.1181
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Effect of nano-grain size on the ionic conductivity of spark plasma sintered 8YSZ electrolyte

Authors K. Rajeswari, M. Buchi Suresh, Dibyendu Chakravarty, Dibakar Das, Roy Johnson
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 1, Pages: 511–517
Time of Publication: 2012-01
Abstract Densification and micro-structural development of ultra fine 8 mol% yttria stabilized zirconia (8YSZ) nano powder were investigated systematically by varying the SPS sintering temperature at constant applied pressure of 50 MPa. A hundred fold decrease in average grain size ranging from 10 μm to 80 nm is observed on decreasing the SPS sintering temperature from 1200 ░C to 1050 ░C with >99% of theoretical densities. Impedance measurements on the samples indicated an enhancement in the ionic conductivity at 700 ░C from 0.004 S/cm to 0.018 S/cm with decrease in grain size from 10 μm to 0.51 μm and a significant increase in conductivity from 0.018 S/cm to 0.068 S/cm on further reduction of grain size to 80 nm. A significant change in the grain-boundary conductivity is noticed on reducing the grain sizes to nano regime. The diverse microstructure with ultra fine grain size resulting from SPS at 1050 ░C could contribute to the enhanced ionic conductivity, which is supported by the activation energy data.
Keywords Solid oxide fuel cells; Electrolyte; Microstructure; Spark plasma sintering
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Dielectric relaxation in a thermosetting polyimide modified with a thermoplastic polyimide

Authors D. A. Belov, S. Yu. Stefanovich and M. Yu. Yablokova
Source
Polymer Science Series A
Volume: 53, Issue: 10, Pages: 963-967
Time of Publication: 2011-10
Abstract Relaxation processes in glass-fiber-reinforced composites with a polymer matrix based on blends of thermosetting and thermoplastic polyimides are studied via dielectric-relaxation spectroscopy. For all investigated blends, two relaxation processes related to the β relaxation of different fragments of the polymer chain are found. Linear flexiblechain polyimide incorporated into the polymer matrix serves as a plasticizer.
Remark DOI: 10.1134/S0965545X11100014
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Autothermal Reforming of Methane in Proton-Conducting Ceramic Membrane Reactor

Authors Jay Kniep , Matthew Anderson , and Jerry Y.S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 50, Issue: 22, Pages: 12426–12432
Time of Publication: 2011-10
Abstract Endothermic steam reforming of methane for hydrogen production requires heat input with selective oxidation of methane. Dense SrCe0.75Zr0.20Tm0.05O3-δ perovskite membranes were combined with a reforming catalyst to demonstrate the feasibility of a heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation of permeated hydrogen. The reforming catalyst used was a prereduced nickel based catalyst supported on γ-Al2O3. Hydrogen produced via the steam reforming of methane or water gas shift reaction was able to diffuse through the catalyst bed and transport through the membrane. The permeated hydrogen reacted with oxygen (from air) to produce heat for the steam reforming of methane on the other side of the membrane. The membrane reactor avoids the use of an expensive air separation unit to produce pure oxygen. The influence of experimental conditions, such as temperature, gas hourly space velocity, and the steam to carbon (S/C) ratio, on the membrane reactor was investigated. SrCe0.75Zr0.20Tm0.05O3-δ showed good chemical stability in steam reforming conditions as X-ray diffraction analysis of the membrane surface exposed to steam-reforming conditions for 425 h showed only minor CeO2 formation. The experimental data demonstrate the feasibility of using a proton conducting ceramic membrane in the heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation.
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Post-heat treatment pressure effect on performances of metal-supported solid oxide fuel cells fabricated by atmospheric plasma spraying

Authors Chun-Huang Tsai, Chang-sing Hwang, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Journal of Power Sources
Volume: 197, Pages: 145–153
Time of Publication: 2012-01
Abstract The nickel metal-supported cells fabricated by atmospheric plasma spraying are post-heat treated in air at 960 ░C for 2 h with different pressures. The current–voltage–power and AC impedance measurements show the prepared cell with an applied pressure of 450 g cm−2 in the post-heat treatment has a better electrochemical performance at test temperatures ≥ 650 ░C. For test temperatures < 650 ░C, the maximum power densities at 450 g cm−2 pressure are about the same as the maximum power densities at 1250 g cm−2 pressure. The SEM micrograph indicates that the cathode including the cathode interlayer and the cathode collector is the most porous region in the cell. AC impedance results show this cathode is the most sensitive part to the applied pressure in the post-heat treatment and the cell with 450 g cm−2 pressure has the smallest low frequency intercept R2 and the polarization resistance Rp at temperatures from 600 to 800 ░C. The performance durability test of the cell post-heat treated at 450 g cm−2 pressure shows a degradation rate of 0.0087 mV h−1 or 0.0026 mW h−1 at 300 mA cm−2 constant current density and 750 ░C test temperature.
Keywords Atmospheric plasma spray; Solid oxide fuel cells; Metal-supported; Nanostructured
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The morphotropic phase boundary in the (1 − x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] perovskite solid solution

Authors T. Sareein, W. Hu, X. Tan and R. Yimnirun
Source
Journal of Materials Science
Volume: 47, Issue: 4, Pages: 1774-1779
Time of Publication: 2012-04
Abstract Ceramics in the (1 − x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] solid solution system with 0.48 ≤ x ≤ 0.56 were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal perovskite phases was identified at x = 0.52. This composition displays the maximum remanent polarization P r of 40.7 μC/cm2 and the best piezoelectric coefficient d 33 of 311 pC/N in the pseudo-binary system. However, the Curie temperature T c for this MPB composition is 291 ░C, much lower than initially expected.
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Synthesis and electrical properties of lead free (Bi0.5K0.5)TiO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 ceramics

Authors A. Prasatkhetragarn, B. Yotburut, N. Triamnak, R. Yimnirun and D.P. Cann
Source
Ceramics International
Volume: 38, Issue: 1, Pages: 827–830
Time of Publication: 2012-01
Abstract Lead free ferroelectric materials with high Curie temperature in (x)[(Bi0.5K0.5)TiO3]− (1-x)[0.5Bi(Zn0.5Ti0.5)O3 − 0.5BaTiO3] or (x)BKT − (1-x)[BZT − BT] ternary system, where x = 0.4, 0.5, 0.6 and 0.8, were synthesized. The single phase perovskite for all ceramics were formed at 900 ░C for 6 h in air. The ceramic compositions with x = 0.5 and 0.6 exhibited the dielectric properties with relaxor-like phase transition behavior, while the ceramic with x = 0.8 showed the dielectric behavior of normal ferroelectric materials. From room temperature P–E measurement, the maximum remnant polarization (Pr of 2.75 μC/cm2) and coercive field (Ec of 12.41 kV/cm) were obtained in the composition with x = 0.6. In addition, the TC, Pr and Ec were found trend to increase with increasing BKT content.
Keywords Ferroelectric; Dielectric; Relaxor-like behavior; High Curie temperature
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Characterization of individual barium titanate nanorods and their assessment as building blocks of new circuit architectures

Authors K. Zagar, F. Hernandez-Ramirez, J. D. Prades, J. R. Morante, A. Rečnik and M. Čeh
Source
Nanotechnology
Volume: 22, Issue: 38, Pages: 385501
Time of Publication: 2011-09
Abstract In this work, we report on the integration of individual BaTiO3 nanorods into simple circuit architectures. Polycrystalline BaTiO3 nanorods were synthesized by electrophoretic deposition (EPD) of barium titanate sol into aluminium oxide (AAO) templates and subsequent annealing. Transmission electron microscopy (TEM) observations revealed the presence of slabs of hexagonal polymorphs intergrown within cubic grains, resulting from the local reducing atmosphere during the thermal treatment. Electrical measurements performed on individual BaTiO3 nanorods revealed resistivity values between 10 and 100 Ω cm, which is in good agreement with typical values reported in the past for oxygen-deficient barium titanate films. Consequently the presence of oxygen vacancies in their structure was indirectly validated. Some of these nanorods were tested as proof-of-concept humidity sensors. They showed reproducible responses towards different moisture concentrations, demonstrating that individual BaTiO3 nanorods may be integrated in complex circuit architectures with functional capacities.
Remark doi: 10.1088/0957-4484/22/38/385501
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Structure, chemical stability and mixed proton–electron conductivity in BaZr0.9−xPrxGd0.1O3−δ

Authors A. Magrasˇ, C. Frontera, A.E. GunnŠs, A. Tarancˇn, D. Marrero-Lˇpez, T. Norby and R. Haugsrud
Source
Journal of Power Sources
Time of Publication: 2011-08
Abstract BaZr0.9−xPrxGd0.1O3−δ (x = 0.3 and 0.6) was prepared by combustion synthesis and characterised with respect to conductivity and stability in an attempt to combine the desirable properties of the end members. The polycrystalline materials exhibit a cubic or pseudo-cubic structure as determined by X-ray synchrotron radiation and transmission electron microscopy. The chemical stability of the compositions is strongly dependent on the praseodymium content, the materials with more Pr present lower stability. Electron holes dominate the conductivity under oxidising atmospheres in BaZr0.3Pr0.6Gd0.1O3−δ, while BaZr0.6Pr0.3Gd0.1O3−δ exhibits a mixed electron hole–proton conducting behaviour. Substitution of Zr by Pr in acceptor-doped BaZrO3 decreases the sintering temperature and increases the grain growth rate.
Remark Article in press, DOI:10.1016/j.jpowsour.2011.06.076
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