| 1. |
- Froitzheim, Jan, 1981, et al.
(author)
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Nano coated interconnects for SOFC (NaCoSOFC)
- 2013
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In: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 57:1, s. 2187-2193
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Conference paper (peer-reviewed)abstract
- The NaCoSOFC project is focused on the development of nano coatings for SOFC interconnects. The project is sponsored by the Nordic Top Level Research Initiative and has four project partners: Sandvik Materials Technology which is producing coated interconnects, Chalmers University of Technology and the University of Oslo that characterize samples with respect to e.g. corrosion, Cr evaporation and ASR as well as Topsoe Fuel Cell that is testing the developed interconnects in its stacks. The developed coatings are based on a combination of Co with RE elements and exhibit high corrosion resistance, 10 fold decrease in Cr evaporation and ASR values that are approximately 50% of the uncoated material.
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| 2. |
- Besikiotis, V., et al.
(author)
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Crystal structure, hydration and ionic conductivity of the inherently oxygen-deficient La2Ce2O7
- 2012
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In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 228, s. 1-7
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Journal article (peer-reviewed)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 degrees 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 degrees 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.
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| 3. |
- Bjorheim, T. S., et al.
(author)
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A combined conductivity and DFT study of protons in PbZrO3 and alkaline earth zirconate perovskites
- 2010
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In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 181:3-4, s. 130-137
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Journal article (peer-reviewed)abstract
- The electrical properties of nominally undoped and 4 mol% Y-doped PbZrO3 have been investigated by AC conductivity measurements and impedance spectroscopy under various p(H2)O and p(O2) at high temperatures. The results indicate that the defect structures are dominated by acceptors (Y dopant and/or Pb vacancies formed during synthesis). In dry atmosphere and at high temperatures, the acceptors are compensated by oxygen vacancies. These are hydrated and replaced by protonic defects (hydroxide ions on oxide ion sites) at higher p(H2)o and lower temperatures. In oxidizing atmospheres, a minority concentration of electron holes dominates the conductivity. At lower temperatures and in wet atmosphere, a significant protonic conductivity contribution is also observed. Based on p(O2) and p(H2)o isotherms, a model for incorporation of protonic defects has been applied, and the standard enthalpy of hydration of oxygen vacancies in undoped PbZrO3 has been determined (-1.07 +/- 0.13 eV). The measured total conductivities are influenced by high grain boundary resistance. Hence, the enthalpy is at the present stage assigned to the polycrystalline ceramic material as such. Rough estimates of bulk proton mobility in Y-doped PbZrO3 yield u(H)(0)+ = 17 cm(2)K/Vs and Delta H-m,H(+) = 0.93 eV. A complementary DFT study of the hydration thermodynamics of PbZrO3 and the alkaline earth zirconate perovskites AZrO(3) (A = Ca, Sr, Ba) is also reported. The experimental and theoretical hydration enthalpies are compared with those of other ABO(3) perovskites. Correlations between the hydration thermodynamics and other properties of the materials are discussed. (C) 2009 Elsevier B.V. All rights reserved.
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| 4. |
- Bjorheim, T. S., et al.
(author)
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Hydration thermodynamics of the proton conducting oxygen-deficient perovskite series BaTi1- xMxO3- x /2 with M = in or Sc
- 2015
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 54:6, s. 2858-2865
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Journal article (peer-reviewed)abstract
- This article establishes the effect of structure and composition on water uptake and the hydration and proton transport properties of the oxygen-deficient perovskite series BaTi1-x(In,Sc)xO3-x/2, with 0.2 ≤ x ≤ 0.7. The equilibrium water uptake is determined by thermogravimetry, while combining thermogravimetry with differential scanning calorimetry allows for direct determination of the materials hydration thermodynamics. Proton and oxide ion transport properties are characterized by means of ac impedance measurements up to 1000 °C. In general, the hydration thermodynamics of the scandates are more favorable than that of the indates and are also affected by changes in crystal structure throughout the series. The more favorable hydration thermodynamics of cubic scandates increase their proton conductivity at higher temperatures compared to their indate counterparts. In contrast to the BaTi1-xInxO3-x/2 series, the BaTi1-xScxO3-x/2 (0.5 ≤ x ≤ 0.7) materials retain their cubic structures upon full saturation by protons and show no signs of chemical instability upon exposure to 1 atm H2O(g) down to 100 °C. The BaTi1-xScxO3-x/2 materials with 0.5 ≤ x ≤ 0.7 may therefore find application in, for instance, steam electrolysis or similar processes involving high water vapor pressures.
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| 5. |
- Hoque, MD khairul, 1984, et al.
(author)
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Structure and conductivity of acceptor doped La2BaZnO5 and Nd2BaZnO5
- 2015
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In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 272, s. 160-165
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Journal article (peer-reviewed)abstract
- The effect of calcium substitution on the structure and electrical conductivity of Ln(2 - x)Ca(x)BaZnO(5 - delta), Ln = La and Nd, has been studied. Differing trends with respect to dependence of the unit cell volume were observed as a function of Ca substitution. For both series of materials the limit of Ca substitution was estimated to be x approximate to 0.2. The electrical conductivity was studied in the temperature range of 1000-350 degrees C using electrochemical impedance spectroscopy in argon and oxygen atmospheres and via isotherms between 400 and 1000 degrees C as function of oxygen pressure and the water vapour pressure. A marked increase in conductivity of approx. two orders of magnitude was explained by the presence of oxygen vacancies in the calcium doped samples. At pO(2)
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| 6. |
- Hultquist, Gunnar, et al.
(author)
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Self-repairing metal oxides
- 2001
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In: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 56:04-mar, s. 313-346
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Journal article (peer-reviewed)abstract
- The oxidation of Cu, Zr, and alloys forming chromia, alumina, and zirconia was studied in a closed reaction chamber in O-2 gas near 20 mbar. Information on the position of oxide growth has been gained from the O-18/SIMS technique. Rates Of O-2 dissociation on metal oxides, Au, and Pt have been evaluated from measurements in labeled O-2. The experimental results indicate that hydrogen in the metal substrates induces increased metal-ion transport in internal oxide surfaces during oxidation, which leads to increased oxide growth at the oxide-gas interface. Experiments also show that oxides of rare-earth metals (REM) and Pt catalyze the dissociation Of O-2. An increased rate of O-2 dissociation can lead to increased transport of oxygen ions in the oxides and increased oxide growth at the substrate-oxide interface. A balanced transport of metal and oxygen ions in metal oxides that leads to oxide growth at both the metal-oxide and at the oxide-gas interface is found to be favorable for the formation of protective oxides with good adherence to the metal substrate. Depending on the original proporation of metal-to-oxygen ion transport in the oxide, an addition of hydrogen will increase or decrease the oxidation kinetics. In analogy, an addition of REM will increase or decrease the oxidation kinetics, depending on the original proportion of metal-to-oxygen ion transport.
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| 7. |
- Huse, M., et al.
(author)
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Neutron diffraction study of the monoclinic to tetragonal structural transition in LaNbO4 and its relation to proton mobility
- 2012
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In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 187, s. 27-34
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Journal article (peer-reviewed)abstract
- The fergusonite-scheelite structural transition of LaNbO4 was characterized by high-intensity variable temperature neutron powder diffraction in an effort to link structural changes to proton transport in the low temperature monoclinic and high temperature tetragonal polymorphs. The pronounced decrease in enthalpy of proton mobility with increasing temperature in monoclinic LaNbO4, identified by Field et al. [1], was found to coincide with the decrease in a key inter-tetrahedral oxygen separation. At temperatures above the transition, this oxygen to oxygen distance remains constant, behavior that is consistent with the invariant nature of the calculated enthalpy of mobility for the tetragonal phase. This oxygen separation is therefore proposed as the key structural parameter determining the success rate of proton transfer and ultimately the proton diffusion in LaNbO4. Infrared measurements performed on acceptor-doped LaNbO4 show an absorption in the region 2500 to 3700 cm(-1) attributed to the O-H stretching motion influenced by hydrogen bonding.
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| 8. |
- Magraso, A., et al.
(author)
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In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28-xW4+xO54+3x/2 (x=0.85)
- 2013
-
In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 1:11, s. 3774-3782
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Journal article (peer-reviewed)abstract
- In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements.
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| 9. |
- Magraso, A., et al.
(author)
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Reduced long term electrical resistance in Ce/Co-coated ferritic stainless steel for solid oxide fuel cell metallic interconnects
- 2015
-
In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 40:27, s. 8579-8585
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Journal article (peer-reviewed)abstract
- The present study is focused on the influence of selected coatings on a ferritic stainless steel (Sanergy HT (TM), Sandvik) on the evolution of the area specific resistance (ASR) as a function of time at high temperature. The samples are exposed in humidified air at 850 degrees C for up to 4200 h. It combines long-term ASR measurements with the thermogravimetric behavior and microstructural analysis of the cross sections by scanning electron microscopy. The results show that uncoated and Co-coated Sanergy HT (TM) exhibit similar oxidation kinetics and comparable ASRs, while a combined Ce/Co coating improves oxidation resistance and, consequently, reduces the ASR significantly. Other reports have earlier shown that Co- (and Ce/Co)-coated Sanergy HT (TM) reduces the evaporation of volatile chromium species. Overall, the study indicates that Ce/Co-coatings will render substantially improved performance for ferritic steel interconnects for solid oxide fuel cells.
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| 10. |
- Rahman, Seikh Mohammad Habibur, 1976, et al.
(author)
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50 mol% indium substituted BaTiO3: Characterization of structure and conductivity
- 2012
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In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 37:9, s. 7975-7982
-
Conference paper (peer-reviewed)abstract
- BaTi0.5In0.5O3-delta was prepared by solid state reaction at 1400 degrees 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) angstrom. 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 degrees C. After hydration the cell parameter increased to 4.1623(1) angstrom. 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 degrees 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 degrees C is much more prominent indicative of dominant proton conduction. At 300 degrees C the total conductivity in wet O-2 was estimated to be 9.30 x 10(-5) S/cm. At T > 800 degrees C the material is a pure oxide ion conductor.
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