Published references
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These publications have a reference to ProboStat™ or other NORECS products
All 1-25 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500 501-525 526-550 551-575 576-600 601-625 626-650 651-675 676-Solid-state photoelectrochemical H2 generation with gaseous reactants
ID=203| Authors |
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Electrochimica Acta
Volume: 97,
Pages: 320–325 Time of Publication: 2013-05 |
| Abstract | Photocurrent and H2 production were demonstrated in an all solid-state photoelectrochemical cell employing gaseous methanol and water vapour at the photoanode. Open circuit photovoltage of around -0.4 V and short circuit photocurrent of up to 250 μA/cm2 were obtained. At positive bias, photocurrent generation was limited by the irradiance, i.e., the amount of photogenerated charge carriers at the anode. Time constants and impedance spectra showed an electrochemical capacitance of the cell of about 15 μF/cm2 in the dark, which increased with increasing irradiance. With only water vapour at the anode, the short circuit photocurrent was about 6% of the value with gaseous methanol and water vapour. The photoanode and electrocatalyst on carbon paper support were affixed to the proton conducting membrane using Nafion® as adhesive, an approach that yielded photocurrents up to 15 times better than that of a cell assembled by hot-pressing, in spite of the overall cell resistance of the latter being up to 5 times less than that of the former. This is attributed, at least partially, to reactants being more readily available at the photoanode of the better performing cell. |
| Keywords | Photoelectrochemical; hydrogen; TiO2; solid-state; Nafion® |
| Remark | Link |
Metallic Interconnects for Proton Ceramic Fuel Cells. Oxidation behavior and transport properties under simulated fuel cell conditions
ID=202| Author |
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Time of Publication: 2013-03
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Dissertation for the degree of Philosophiae Doctor Link |
Synthesis and characterization of perovskite-type SrxY1−xFeO3−δ (0.63≤x<1.0) and Sr0.75Y0.25Fe1−yMyO3−δ (M= Cr, Mn, Ni), (y=0.2, 0.33, 0.5)
ID=201| Authors |
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Journal of Solid State Chemistry
Volume: 200,
Pages: 30-38 Time of Publication: 2013-04 |
| Abstract | Abstract Oxygen-deficient ferrates with the cubic perovskite structure SrxY1−xFeO3−δ were prepared in air (0.71≤x≤0.91) as well as in N2 (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along <1 0 0>p with G± ~0.4<1 0 0>p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K−1 in air at 298–673 K. At 773–1173 K TEC increases up to 17.2 ppm K−1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1−yMyO3−δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79. |
| Keywords | Perovskites; Neutron diffraction; Electron diffraction; High-temperature conductivity; Thermal expansion; Magnetic susceptibility |
| Remark | Link |
Optimization of synthesis conditions for rare-earth titanate based oxygen ion conductors
ID=200| Authors |
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Solid State Ionics
Volume: 230,
Pages: 52-58 Time of Publication: 2013-01 |
| Abstract | High-density (Yb0.9Ca0.1)2Ti2O6.9, (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions have been prepared through co-precipitation followed by firing for 4 h at 1500 and 1550 °C, and their crystal structure (XRD), microstructure (SEM), and oxygen ion conductivity (impedance spectroscopy) have been studied in relation to the firing temperature and precipitant used. As in the case of (Yb0.9Ca0.1)2Ti2O6.9 and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, the optimal synthesis temperature for (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ is 1500 °C. The bulk oxygen ion conductivity of the pyrochlore-like solid solutions (Yb0.9Ca0.1)2Ti2O6.9 is a stronger function of synthesis temperature than that of the (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions with more complex A sublattice. The rise of the synthesis temperature from 1500 to 1550 °C has detrimental effect on the grain boundary conductivity of the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ ceramics. That effect is connected with a considerable grain-boundary segregation of a calcium-containing phase in the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ. The bulk and grain boundary conductivity of (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ are independent of the precursor synthesis conditions (homogeneous and non-homogeneous co-precipitation). |
| Keywords | Synthesis; Co-precipitation; Pyrochlore; Doping; Oxide ion conductivity; Impedance spectroscopy |
| Remark | Link |
Multilayered thin films for oxidation protection of Mg2Si thermoelectric material at middle–high temperatures
ID=199| Authors |
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Thin Solid Films
Volume: 526,
Pages: 150–154 Time of Publication: 2012-12 |
| Abstract | Multilayered molybdenum silicide-based thin films were deposited via radio frequency magnetron sputtering in order to obtain efficient barrier against oxidation process which affected Mg2Si thermoelectric materials at middle–high temperatures. X ray diffraction, energy dispersive spectroscopy, secondary ion mass spectroscopy, field emission scanning electron microscopy (FE-SEM) and electrical measurements at high temperature were carried out in order to obtain, respectively, the structural, compositional, morphological and electrical characterization of coatings. Furthermore, the mechanical behavior of the thin film/Mg2Si-pellet system was observed in situ as a function of temperature by FE-SEM employing a heating module. Moreover, the barrier properties for oxygen protection after thermal treatment in air at high temperature were qualitatively evaluated. |
| Keywords | Thin film; Thermoelectric material; Magnesium silicide; Molybdenum silicide; Middle–high temperature |
| Remark | Link |
Thin films of SnO2-CeO2 binary oxides obtained by pulsed laser deposition for sensing application
ID=198| Authors |
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Applied Surface Science
Time of Publication: 2012-11
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| Abstract | Binary tin oxide – cerium oxide thin films with ceria concentrations in the range 10- 30% have been obtained by pulsed laser deposition technique, with or without additional oxygen RF plasma beam assistance. A good preservation of the Ce/Sn atomic concentration and Ce3+ content on the film surface of about 30% was obtained for almost all the investigated conditions of substrate temperature and RF powers. The sharp decrease of the electrical resistance in hydrogen environment at temperatures above 300 °C indicates a direct interaction between hydrogen and metal oxides surfaces leading to OH groups formation, as evidenced by XPS measurements. The highest sensitivity (∼40) was attained for the sample with 10% ceria and RF assistance, while the lowest operating temperature (∼250-320 °C) was encountered for that with 30% ceria deposited in the presence of RF discharge. |
| Keywords | RF assisted pulsed laser deposition; SnO2-CeO2 binary oxides; Ce3+ and Ce4+ concentration; sensitivity in H2 atmosphere |
| Remark |
Available online Link |
Phase formation, electrical properties and morphotropic phase boundary of 0.95Pb(ZrxTi1−x)O3–0.05Pb(Mn1/3Nb2/3)O3 ceramics
ID=197| Authors |
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Ceramics International
Volume: 39,
Pages: S91–S95 Time of Publication: 2013-05 |
| Abstract | Ferroelectric ceramics in specific composition of 0.95Pb(ZrxTi1−x)O3–0.05Pb(Mn1/3Nb2/3)O3 or PZT–PMnN (with x=0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary (MPB) composition. The effects of Zr/Ti ratio on phase formation, dielectric and ferroelectric properties of the specimens have also been investigated and discussed. X-ray diffraction patterns indicate that the MPB of the tetragonal and rhombohedral phase lies in x=0.52. The crystal structure of PZT–PMnN appeared to change gradually from tetragonal to rhombohedral phase with increasing Zr content. The dielectric and ferroelectric properties measurements also show a maximum value (εr, tan δ and Pr) at Zr/Ti=52/48, while the transition temperature decreases with increasing Zr content. |
| Keywords | Dielectric properties; Ferroelectric properties; MPB |
| Remark | Link |
Oxygen ion conductivity of (Yb0.9 − xTbxCa0.1)2Ti2O7 − δ solid solutions
ID=196| Authors |
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Inorganic Materials
Volume: 48,
Issue: 11,
Pages: 1126-1130 Time of Publication: 2012-11 |
| Abstract | We have studied terbium substitution for ytterbium in (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550°C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb0.9Ca0.1)2Ti2O6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: Δr = r(TbCN 83+) − r(YbCN 83+) = 0.055 Å. The oxygen ion conductivity of the (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900°C. At high temperatures (t > 640°C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640°C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration. |
| Remark | Link |
H and Li Related Defects in ZnO and their Effect on Electrical Properties
ID=195| Authors |
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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. |
| Remark | Link |
Crystal structure, hydration and ionic conductivity of the inherently oxygen-deficient La2Ce2O7
ID=194| Authors |
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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 |
| Remark | Link |
Microstructure and electrical properties of zirconia and composite nanostructured ceramics sintered by different methods
ID=192| Authors |
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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. |
| Remark | Link |
Characteristics of SrCo1 − xSnxO3 − δ cathode materials for use in solid oxide fuel cells
ID=191| Authors |
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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 |
| Remark | Link |
Investigation of La1−xSrxCrO3−∂ (x ~ 0.1) as Membrane for Hydrogen Production
ID=190| Authors |
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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 |
| Remark | Link |
CO2 decomposition via oxygen deficient ferrite electrodes using solid oxide electrolyser cell
ID=189| Source |
Time of Publication: 2012-09
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| 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
ID=188| Author |
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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. |
| Remark | Link |
Fabrication, sealing and high pressure testing of tubular La2NiO4+δ membranes for air separation
ID=187| Authors |
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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 |
| Remark | Link |
Effects of the microwave heating on the properties of gadolinium-doped cerium oxide prepared by polyol method
ID=186| Authors |
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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 |
| Remark | Link |
Investigating Reliability on Fuel Cell Model Identification. Part II: An Estimation Method for Stochastic Parameters
ID=185| Authors |
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Fuel Cells
Time of Publication: 2012-08
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| 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
ID=184| Authors |
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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. |
| Remark | Link |
BaTiO3–Bi(Zn1/2Ti1/2)O3–BiScO3 Ceramics for High-Temperature Capacitor Applications
ID=183| Authors |
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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 (>200°C). 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. |
| Remark | Link |
Sr1−xPrxCo0.95Sn0.05O3−δ ceramic as a cathode material for intermediate-temperature solid oxide fuel cells
ID=182| Authors |
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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
ID=181| Authors |
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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
ID=180| Authors |
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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
ID=179| Authors |
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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
ID=178| Authors |
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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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