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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
Remark Link

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
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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
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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
Link

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
Link

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
Link

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
Link

SrCo1−xSbxO3−δ cathode materials prepared by Pechini method for solid oxide fuel cell applications

Authors Sea-Fue Wang, Hsi-Chuan Lu, Yung-Fu Hsu, Chien-Chung Huang, Chun-Ting Yeh
Source
Ceramics International
Volume: 38, Issue: 7, Pages: 5941–5947
Time of Publication: 2012-09
Abstract In this study, SrCo1−ySbyO3−δ powders were prepared by a modified Pechini method. According to the study results, the cubic Pm3m phase of the SrCo1−ySbyO3−δ ceramics was obtained as 10% of cobalt ions were substituted by antimony ions. Doping of Sb3+ ions appeared both to stabilize the Pm3m phase of the SrCo1−ySbyO3−δ ceramics and to enhance densification and retard grain growth. The coefficient of thermal expansion of the SrCo1−xSbxO3−δ ceramics increased with the content of the antimony ions, ranging from 10.17 to 15.37 ppm/C at temperatures lower than the inflection point (ranging from 450 C to 550 C) and from 22.16 to 29.29 ppm/C at higher temperatures. For the SrCo0.98Sb0.02O3−δ ceramic, electrical conductivity reached a maximum of 507 S/cm at 450 C. The ohmic and polarization resistances of the single cell with the pure SrCo0.98Sb0.02O3−δ cathode at 700 C read respectively 0.298 Ω cm2 and 0.560 Ω cm2. The single cell with the SrCo0.98Sb0.02O3−δ-SDC composite cathode appeared to reduce the impedances with the R0 and RP at 700 C reading respectively 0.109 Ω cm2 and 0.127 Ω cm2. Without microstructure optimization and measured at 700 C, the single cells with the pure SrCo0.98Sb0.02O3−δ cathode and the SrCo0.98Sb0.02O3−δ-SDC composite cathode, demonstrated maximum power densities of 0.100 W/cm2 and 0.487 W/cm2. Apparently, SrCo1−ySbyO3−δ is a potential cathode for use in IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Available online 19 April 2012
Link

Synthesis, Sintering, Transport Properties, and Surface Exchange of La2Ni0.9Cu0.1O4+δ

Authors Zuoan Li, Truls Norby, Reidar Haugsrud
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 6, Pages: 2065–2073
Time of Publication: 2012-06
Abstract Dense La2Ni0.9Cu0.1O4+δ ceramics were sintered from powders synthesized through a wet-chemical citrate nitrate route with optimized ratios of citrate to nitrate. Less citrate decreases the required sintering temperature and improves the oxygen permeativity. The oxygen permeation was measured as a function of oxygen activity gradient, membrane thickness (0.4–2.6 mm) and temperature (800C–950C). The oxygen self diffusion coefficient DO and the surface exchange coefficient k show Arrhenius-type behaviors with activation energies of ~50 and ~100 kJ/mol, respectively. The oxygen chemical diffusion coefficient Dchem and surface exchange coefficient kchem, measured by conductivity relaxation, exhibit Arrhenius-type behaviors with activation energies of 62 and 104 kJ/mol, respectively. Dchem and kchem are related to DO and k through the thermodynamic factor ωO.
Remark Link

LaCoO3 ceramics obtained from reactive powders

Authors L. Predoana, B. Malic, D. Crisan, N. Dragan, M. Anastasescu, J. Calderon-Moreno, R. Scurtu, M. Zaharescu
Source
Ceramics International
Volume: 38, Issue: 7, Pages: 5433–5443
Time of Publication: 2012-09
Abstract The aim of the present study was to establishing the correlation between the structure and properties of the LaCoO3 powders obtained by aqueous sol–gel method with citric acid and their sintering behavior in order to obtain fully densified ceramics with perovskite structure. Two types of cobalt and lanthanum reagents were used in synthesis, namely nitrates and acetates. The sintering was realized at temperatures ranging between 800 and 1200 C for 2 h. The sintered samples were investigated by classical ceramic methods (shrinkage, density, porosity) and by structural and morphological investigations: XRD, SEM, AFM and XPS. The electrical properties of the samples were determined by impedance spectroscopy. The ceramics obtained with powders starting with acetates have presented a lower sintering ability as compared with the samples obtained from powders starting with nitrates. LaCoO3 ceramics with best properties was obtained from powders starting with nitrates sintered at 1100 C.
Remark Available online 11 April 2012
Link

Preparation and characterization of composite membranes based on sulfonated PEEK and AlPO4 for PEMFCs

Authors Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Niels De Greef, Jin Won Seo, Jean-Pierre Locquet
Source
Solid State Ionics
Volume: 219, Pages: 83–89
Time of Publication: 2012-05
Abstract Sulfonated poly(ether ether ketone) (PEEK) and their composites are considered one of the most promising alternatives for Nafion, the industry benchmark for electrolytic membranes in proton exchange membrane (PEM) fuel cells. In the present study, PEEK was non-homogeneously sulfonated using concentrated H2SO4 at different temperatures (room temperature, 60 C, and 80 C) and time durations (5, 7, 48, and 72 h). Composite membranes of SPEEK with different weight ratios of AlPO4 synthesized by sol–gel were also prepared. Depending on the degree of sulfonation (DS), the Ion Exchange Capacity (IEC) of the membranes varied from 1.06 to 2.9 meq g− 1. XRD results show the increasing amorphous nature of the membranes with increase in IEC and DS value. The water uptake of the membranes also increased with DS. Simultaneous TGA–FTIR measurement of the composite membranes showed better thermal stability compared to pure SPEEK membranes. The water uptake and proton conductivity of the composite SPEEK membranes were found to be lower than that of pure SPEEK membranes, while the composite membranes exhibited a better swelling behavior and mechanical stability than the pure SPEEK samples.
Keywords Proton exchange membrane (PEM); Composite membranes; Sulfonated poly(etheretherketone) (SPEEK); Proton conductivity; Ion exchange capacity (IEC); Sol–gel
Remark Link

Synthesis and electrical properties of a new fluorite-like anionic conductor in the Nd2O3–MoO3 system (43–47 mol% Nd2O3)

Authors V.I. Voronkova, , E.P. Kharitonova, D.A. Belov
Source
Solid State Ionics
Volume: 225, Pages: 654–657
Time of Publication: 2012-10
Abstract This work addresses phase relations in the Nd2O3–MoO3 system (25–50 mol% Nd2O3) and properties of a fluorite-like compound existing in this system in the composition range of 43–47 mol% Nd2O3. We describe for the first time the crystal growth of this compound. The composition of the crystals is Nd10Mo6O33 (Nd2O3:MoO3 = 5:6, 45.5 mol% Nd2O3), which falls within the above composition range. Dielectric spectroscopy data for polycrystalline Nd14Mo8O45 (within the homogeneity range of the fluorite-like compound) suggest a phase transition at 650–700 C. The exact mechanism of the transition remains to be clarified. Nd14Mo8O45 has rather high bulk conductivity, approaching 10− 2 S/cm at 800 C. The low activation energy and key structural features of the compound in question indicate that it is an anionic conductor.
Keywords Fluorite-like compounds; Rare-earth molybdates; Single crystals; Relaxation; Anionic conductor
Remark Available online 22 March 2012
Link

Temperature dependent thermoelectric material power factor measurement system

Authors Jonathan D'Angelo, Adam Downey, Timothy Hogan
Source
Review of scientific instruments
Volume: 81, Issue: 075107 Publisher: American Institute of Physics, Time of Publication: 2010-06
Abstract Thermoelectric materials can be used for cooling/heating applications, or converting waste heat into electricity. Novel thermoelectric materials have been discovered in recent years. Characterization of an electrical conductivity and thermopower of a sample from room temperature to ≥ 900 K is often necessary for thermoelectric materials. This paper describes a system built for measurement of the power factor of thermoelectric materials from 300 to 1273 K. Characterization results of the system are also presented.

High temperature electronic properties of BaTiO3 – Bi(Zn1/2Ti1/2)O3 – BiInO3 for capacitor applications

Author Natthaphon Raengthon and David P. Cann
Source
Journal of Electroceramics
Volume: 28, Issue: 2-3, Pages: 165-171
Time of Publication: 2012-03
Abstract Solid solutions xBaTiO3 – (1-x)(0.5Bi(Zn1/2Ti1/2)O3 – 0.5BiInO3), where x = 0.95–0.60, were prepared by conventional mixed oxide method. The single phase perovskite structure was obtained for the composition with x ≥ 0.75. Phase transformation from tetragonal to pseudocubic was observed from x-ray diffraction patterns when x decreased from 0.95 to 0.75. In tetragonal phase region, x ≥ 0.90, the increase of Bi(Zn1/2Ti1/2)O3 – BiInO3 content decreased the tetragonality and the temperature at which the relative permittivity is maximum (Tmax). The increase in lattice parameter and Tmax were observed in the pseudocubic phase region, x < 0.90. Additionally, a highly broad and diffuse phase transition was observed from the dielectric data in the pseudocubic phase region. The introduction of Ba vacancies in compositions with x = 0.80 and 0.75 also improved dielectric loss at high temperatures. The incorporation of BiInO3 into the BaTiO3 – Bi(Zn1/2Ti1/2)O3 compound was also found to improve the temperature coefficient of the relative permittivity, with values as low as approximately −1,000 ppm/K. Overall, ternary perovskite solid solutions based on adding Bi(Zn1/2Ti1/2)O3 – BiInO3 to BaTiO3 shows excellent potential for high temperature capacitor applications
Keywords High temperature capacitor – Bi-based perovskite – BiInO3 – Bi(Zn1/2Ti1/2)O3 – BaTiO3 – Insulation resistance
Remark Link

Stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) and (Tb0.9Ca0.1)2Ti2O7−δ pyrochlores under redox conditions

Authors S.N. Savvin, A.V. Shlyakhtina, D.A. Belov, J.C. Ruiz-Morales, L.G. Shcherbakova, P. Nuez
Source
Solid State Ionics
Volume: 225, Pages: 457–463
Time of Publication: 2012-10
Abstract The stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) pyrochlores under different redox conditions (air, dry and wet H2) has been studied. The bulk conductivity of the terbium-containing materials is slightly higher under reducing conditions (5% H2 + 95% Ar) than in air, reaching ~ 6 10− 2 and 2.5 10− 2 S/cm at 800 C for (Yb0.8Ca0.1Tb0.1)2Ti2O7−δ and (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ, respectively. In air–hydrogen–air cycles, the bulk conductivity returns to its original level in air: ~ 2 10− 2 and 1 10− 2 S/cm at 800 C in (Yb0.8Ca0.1Tb0.1)2Ti2O7−δ and (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ, respectively. Exposure of (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ to a flowing mixture of 5% H2 and 95% Ar for 100 h slightly reduces its conductivity: from 0.029 to 0.023 S/cm at 900 C. The cerium-containing materials (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ and (Dy0.8Ca0.1Ce0.1)2Ti2O7−δ were found to be unstable under reducing conditions. The bulk conductivity of (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ is practically independent on the atmosphere while the grain boundary conductivity increased from 5.6 10− 8 in air to ~ 1 10− 5 S/cm at 425 C on reducing the sample in 5%H2–Ar gas mixture. However, after two redox cycles air–5%H2–Ar–air the sintered pellet of (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ fractured whereas (Dy0.8Ca0.1Ce0.1)2Ti2O7−δ degraded immediately under reducing conditions. It was observed that the size mismatch between Ln and Ln´ cations strongly affects the bulk to grain boundary conductivity ratio in (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) pyrochlores.
Keywords Pyrochlore; Donor doping; High-temperature conductivity; Ionic conductivity; Solid electrolyte; Electronic conductivity
Remark Available online 8 March 2012; http://dx.doi.org/10.1016/j.ssi.2012.02.009
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Spark Plasma Sintering and Hot Pressing of Hetero-Doped LaNbO4

Authors Guttorm E. Syvertsen, Claude Estourns, Harald Fjeld, Reidar Haugsrud, Mari-Ann Einarsrud, Tor Grande
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 5, Pages: 1563–1571
Time of Publication: 2012-05
Abstract LaNbO4/La3NbO7 and LaNbO4/LaNb3O9 cer-cer composites were prepared by impregnating Ca-doped LaNbO4 powder, synthesized by spray pyrolysis, with La- or Nb-precursor solutions. The sintering of the calcined powders was investigated by dilatometry, and dense composites were prepared by conventional sintering, hot pressing, and spark plasma sintering. The particle size of the starting powders was about 50 nm, and the average grain size of the dense materials ranged from 100 nm and upwards, depending on the sintering temperature, sintering procedure, and the phase composition. The unit cell parameters of LaNbO4 showed a finite size effect and approached the cell parameters of tetragonal LaNbO4 with decreasing crystallite size, both for the single-phase material and the composites. The minority phase (La3NbO7 or LaNb3O9) were observed as isolated grains and accumulated at triple points and not along the grain boundaries, pointing to a large dihedral angle between the phases. The calcium-solubility in the minority phases was larger than in LaNbO4, which corresponds well with previous reports. The electrical conductivity of the hetero-doped materials was similar to, or lower than, that for Ca-doped LaNbO4.
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Sandvik Sanergy HT – A potential interconnect material for LaNbO4-based proton ceramic fuel cells

Authors Anders Werner Bredvei Skilbred, Reidar Haugsrud
Source
Journal of Power Sources
Volume: 206, Pages: 70–76
Time of Publication: 2012-05
Abstract High temperature properties of Sandvik Sanergy HT have been studied to evaluate the alloy's suitability as an interconnect material for LaNbO4 based proton ceramic fuel cells (PCFCs). The thermal expansion behavior of the alloy deviates from LaNbO4 at higher temperatures which may be unfavorable, however the average values for the two materials over the whole temperature region are rather similar. The oxidation kinetics was parabolic and the rate constants were low at temperatures below 1000 C. Accelerated oxidation was encountered after 300 h at 1000 C revealing that the material may undergo severe degradation at sufficiently high temperatures. A complex oxide scale containing an inner layer of chromium oxide and an outer layer of various spinel phases containing chromium, manganese and iron was formed at all temperatures. As a consequence of high oxidation resistance and an oxide with relatively high electronic conductivity, the area specific resistance (ASR) of Sandvik Sanergy HT measured at 700 C proved to be low.
Keywords Proton ceramic fuel cell; Interconnect; Sandvik Sanergy HT; Oxidation kinetics; Thermal expansion; Area specific resistance
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A novel perovskite-based proton conductor for solid oxide fuel cells

Authors Ramya Hariharan, T.R.S. Prasanna, Prakash Gopalan
Source
Scripta Materialia
Volume: 66, Issue: 9, Pages: 658–661
Time of Publication: 2012-05
Abstract A perovskite-based electrolyte, Ca-substituted YAlO3, has been synthesized by the citrate gel process. The conductivity of Y0.9Ca0.1AlO3-δ has been studied by AC impedance spectroscopy in controlled atmospheres in the temperature range 300–800 C. The material has been found to be a mixed conductor with dominant p-type electronic conduction at elevated temperatures and a combined protonic conduction below 600 C in wet conditions. The H/D isotope effect on conductivity confirms the presence of protonic conductivity between 400 and 600 C.
Keywords Proton conduction; Electrical properties; Solid electrolyte; Perovskite oxide; Fuel cell materials
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50 mol% indium substituted BaTiO3: Characterization of structure and conductivity

Authors S.M.H. Rahman, C.S. Knee, I. Ahmed, S.G. Eriksson, R. Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7975–7982
Time of Publication: 2012-05
Abstract BaTi0.5In0.5O3−δ was prepared by solid state reaction at 1400 C. Rietveld analysis of high resolution X-ray powder diffraction data indicated phase pure as-prepared material that adopts a cubic perovskite structure with a = 4.1536(1) . Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 57% of the theoretically achievable protonation was attained on exposure to a humid environment at 185 C. After hydration the cell parameter increased to 4.1623(1) . Electrical conductivity was measured both with fixed and variable frequency ac impedance methods as a function of temperature, oxygen-, water vapour- and heavy water vapour partial pressures. In the temperature range 400–800 C a slight increase in the total conductivity with increasing oxygen partial pressure is encountered, characteristic of a contribution from p-type charge carriers. The effect of the water vapour pressure on conductivity below 600 C is much more prominent indicative of dominant proton conduction. At 300 C the total conductivity in wet O2 was estimated to be 9.30 10−5 S/cm. At T > 800 C the material is a pure oxide ion conductor.
Keywords Barium titanate; Perovskite; Brownmillerite; Proton conductivity; X-ray diffraction; Impedance spectroscopy
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