161 results on '"Kubicek, Markus"'
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2. Investigation of atomic-scale decorations on mixed conducting oxides via time-of-flight secondary ion mass spectrometry (ToF-SIMS)
- Author
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Fahrnberger, Florian, Siebenhofer, Matthäus, Hutter, Herbert, and Kubicek, Markus
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- 2023
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3. Mechanism of photo-ionic stoichiometry changes in SrTiO3
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Viernstein, Alexander, Kubicek, Markus, Morgenbesser, Maximilian, Huber, Tobias M., Ellmeyer, Emil, Siebenhofer, Matthäus, Vaz, Carlos A.F., and Fleig, Jürgen
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- 2022
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4. Exploring point defects and trap states in undoped SrTiO3 single crystals
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Siebenhofer, Matthäus, Baiutti, Federico, de Dios Sirvent, Juan, Huber, Tobias M., Viernstein, Alexander, Smetaczek, Stefan, Herzig, Christopher, Liedke, Maciej Oskar, Butterling, Maik, Wagner, Andreas, Hirschmann, Eric, Limbeck, Andreas, Tarancon, Albert, Fleig, Jürgen, and Kubicek, Markus
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- 2022
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5. SrTiO3 based high temperature solid oxide solar cells: Photovoltages, photocurrents and mechanistic insight
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Morgenbesser, Maximilian, Schmid, Alexander, Viernstein, Alexander, de Dios Sirvent, Juan, Chiabrera, Francesco, Bodenmüller, Niklas, Taibl, Stefanie, Kubicek, Markus, Baiutti, Federico, Tarancon, Albert, and Fleig, Jürgen
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- 2021
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6. Substrate stoichiometry changes during pulsed laser deposition: a case study on SrTiO[formula omitted]
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Siebenhofer, Matthäus, Huber, Tobias, Artner, Werner, Fleig, Jürgen, and Kubicek, Markus
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- 2021
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7. Oxygen surface exchange kinetics of La1−xSrxCoO3–δ thin-films decorated with binary oxides: links between acidity, strontium doping, and reaction kinetics.
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Merieau, Alexandre, Siebenhofer, Matthäus, Böhme, Christin, Kubicek, Markus, Joubert, Olivier, Fleig, Juergen, and Nicollet, Clément
- Abstract
Recent studies showed that binary oxide modifications can induce substantial changes in the oxygen exchange kinetics at the surface of Pr
0.1 Ce0.9 O2−δ electrodes. The effect of these oxides was linked to their Smith acidity. In this work, these observations of oxides at the surface of mixed conducting oxides are extended to a metal-like conducting oxide La1−x Srx CoO3−δ . The samples of La1−x Srx CoO3−δ with various Sr contents deposited by PLD were investigated in situ during the deposition process by impedance spectroscopy, before and after decoration with SrO, CaO and SnO2 at different temperatures and pO2 . Considering experimental observations from the literature, the kinetics of decorated surfaces follow the Smith acidity of the binary oxide, which confirms that this scale is a good descriptor for sorting impurities. No notable effects of the Sr content on the decoration impact were measured and the effect of impurities was compared between La1−x Srx CoO3−δ and Pr0.1 Ce0.9 O2−δ from a previous study. Basic impurities added at the surface of La1−x Srx CoO3−δ electrodes showed less influence on the reaction kinetics than on Pr0.1 Ce0.9 O2−δ , but a stronger impact was found with acidic oxides. This effect is supposed to originate from the acidity difference that controls a major part of the oxygen exchange kinetics. These results underline that the outermost surface is decisive for solid oxide cell electrode materials and that the relative insensitivity of the kinetics to bulk properties might lead to a high flexibility in terms of electrode design and material combination. [ABSTRACT FROM AUTHOR]- Published
- 2024
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8. Structural Characterization of La 0.6 Sr 0.4 CoO 3− δ Thin Films Grown on (100)-, (110)-, and (111)-Oriented La 0.95 Sr 0.05 Ga 0.95 Mg 0.05 O 3− δ.
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Ražnjević, Sergej, Drev, Sandra, Bumberger, Andreas E., Popov, Maxim N., Siebenhofer, Matthäus, Böhme, Christin, Chen, Zhuo, Huang, Yong, Riedl, Christoph, Fleig, Jürgen, Čeh, Miran, Kubicek, Markus, and Zhang, Zaoli
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THIN films ,ELECTROLYSIS ,ELECTRON energy loss spectroscopy ,ATOMIC force microscopy ,SOLID oxide fuel cells ,TRANSMISSION electron microscopy - Abstract
In this study, a detailed structural characterization of epitaxial La 0.6 Sr 0.4 CoO 3 − δ (LSC) films grown in (100), (110), and (111) orientations was conducted. LSC is a model air electrode material in solid oxide fuel and electrolysis cells and understanding the correlation of bulk structure and catalytic activity is essential for the design of future electrode materials. Thin films were grown on single crystals of the perovskite material La 0.95 Sr 0.05 Ga 0.95 Mg 0.05 O 3 − δ cut in three different directions. This enabled an examination of structural details at the atomic scale for a realistic material combination in solid oxide cells. The investigation involved the application of atomic force microscopy, X-ray diffraction, and high-resolution transmission electron microscopy to explore the distinct properties of these thin films. Interestingly, ordering phenomena in both cationic as well as anionic sublattices were found, despite the fact that the thin films were never at higher temperatures than 600 °C. Cationic ordering was found in spherical precipitates, whereas the ordering of oxygen vacancies led to the partial transition to brownmillerite in all three orientations. Our results indicate a very high oxygen vacancy concentration in all three thin films. Lattice strains in-plane and out-of-plane was measured, and its implications for the structural modifications are discussed. [ABSTRACT FROM AUTHOR]
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- 2024
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9. The Chemical Evolution of the La0.6Sr0.4CoO3−δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity
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Opitz, Alexander K., Rameshan, Christoph, Kubicek, Markus, Rupp, Ghislain M., Nenning, Andreas, Götsch, Thomas, Blume, Raoul, Hävecker, Michael, Knop-Gericke, Axel, Rupprechter, Günther, Klötzer, Bernhard, and Fleig, Jürgen
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- 2018
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10. Author Correction: Strain-induced structure and oxygen transport interactions in epitaxial La0.6Sr0.4CoO3−δ thin films
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Ivanov, Yurii P., Kubicek, Markus, Siebenhofer, Matthäus, Viernstein, Alexander, Hutter, Herbert, Fleig, Jürgen, Chuvilin, Andrey, and Zhang, Zaoli
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- 2020
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11. Strain-induced structure and oxygen transport interactions in epitaxial La0.6Sr0.4CoO3−δ thin films
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Ivanov, Yurii P., Kubicek, Markus, Siebenhofer, Matthäus, Viernstein, Alexander, Hutter, Herbert, Fleig, Jürgen, Chuvilin, Andrey, and Zhang, Zaoli
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- 2020
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12. A Guideline to Mitigate Interfacial Degradation Processes in Solid‐State Batteries Caused by Cross Diffusion.
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Din, Mir Mehraj Ud, Ladenstein, Lukas, Ring, Joseph, Knez, Daniel, Smetaczek, Stefan, Kubicek, Markus, Sadeqi‐Moqadam, Mohsen, Ganschow, Steffen, Salagre, Elena, Michel, Enrique G., Lode, Stefanie, Kothleitner, Gerald, Dugulan, Iulian, Smith, Jeffrey G., Limbeck, Andreas, Fleig, Jürgen, Siegel, Donald J., Redhammer, Günther J., and Rettenwander, Daniel
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SOLID state batteries ,PHASE transitions ,PROTECTIVE coatings ,TRANSITION metals ,ACTIVATION energy ,DIFFUSION coefficients - Abstract
Diffusion of transition metals across the cathode–electrolyte interface is identified as a key challenge for the practical realization of solid‐state batteries. This is related to the formation of highly resistive interphases impeding the charge transport across the materials. Herein, the hypothesis that formation of interphases is associated with the incorporation of Co into the Li7La3Zr2O12 lattice representing the starting point of a cascade of degradation processes is investigated. It is shown that Co incorporates into the garnet structure preferably four‐fold coordinated as Co2+ or Co3+ depending on oxygen fugacity. The solubility limit of Co is determined to be around 0.16 per formula unit, whereby concentrations beyond this limit causes a cubic‐to‐tetragonal phase transition. Moreover, the temperature‐dependent Co diffusion coefficient is determined, for example, D700 °C = 9.46 × 10−14 cm2 s−1 and an activation energy Ea = 1.65 eV, suggesting that detrimental cross diffusion will take place at any relevant process condition. Additionally, the optimal protective Al2O3 coating thickness for relevant temperatures is studied, which allows to create a process diagram to mitigate any degradation with a minimum compromise on electrochemical performance. This study provides a tool to optimize processing conditions toward developing high energy density solid‐state batteries. [ABSTRACT FROM AUTHOR]
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- 2023
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13. Light may harm or help
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Fleig, Jürgen and Kubicek, Markus
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- 2018
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14. Electrochemical properties of La0.6Sr0.4CoO3 − δ thin films investigated by complementary impedance spectroscopy and isotope exchange depth profiling
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Kubicek, Markus, Huber, Tobias M., Welzl, Andreas, Penn, Alexander, Rupp, Ghislain M., Bernardi, Johannes, Stöger-Pollach, Michael, Hutter, Herbert, and Fleig, Jürgen
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- 2014
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15. Defect Chemistry of Spinel Cathode MaterialsA Case Study of Epitaxial LiMn2O4 Thin Films.
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Bumberger, Andreas E., Boehme, Christin, Ring, Joseph, Raznjevic, Sergej, Zhang, Zaoli, Kubicek, Markus, and Fleig, Juergen
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- 2023
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16. Improving and degrading the oxygen exchange kinetics of La0.6Sr0.4CoO3−δ by Sr decoration.
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Siebenhofer, Matthäus, Riedl, Christoph, Nenning, Andreas, Artner, Werner, Rameshan, Christoph, Opitz, Alexander Karl, Fleig, Jürgen, and Kubicek, Markus
- Abstract
Minimizing the overpotential at the air electrode of solid oxide fuel cells (SOFC) is one of the key challenges regarding a broad applicability of this technology. Next to novel materials and geometry optimization, surface modification is a promising and flexible method to alter the oxygen exchange kinetics at SOFC cathode surfaces. Despite extensive research, the mechanism behind the effect of surface decorations is still under debate. Moreover, for Sr decoration, previous studies yielded conflicting results, reporting either a beneficial or a detrimental impact on the oxygen exchange kinetics. In this contribution, in situ impedance spectroscopy during pulsed laser deposition was used to investigate the effect of Sr containing decorations under different deposition conditions. Depending on deposition temperature and interactions with the gas phase, opposing effects of Sr decoration were found. In combination with near-ambient pressure X-ray photoelectron spectroscopy and non-ambient X-ray diffractometry, it was possible to trace this phenomenon back to different chemical environments of the surface Sr. At high temperatures, Sr is deposited as SrO, which can have a beneficial effect on the oxygen exchange kinetics. At low temperatures, SrCO
3 adsorbates are formed from trace amounts of CO2 in the measurement atmosphere, causing a decrease of the oxygen exchange rate. These results are in excellent agreement with the concept of surface acidity as a descriptor for the effect of surface decorations, providing further insight into the oxygen exchange kinetics on SOFC cathode surfaces and its degradation. In addition, this study shows that Sr segregation itself initially does not lead to performance degradation but that segregated SrO readily reacts with acidic compounds, reducing the catalytic capability of mixed conducting oxides. [ABSTRACT FROM AUTHOR]- Published
- 2023
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17. Crystal-Orientation-Dependent Oxygen Exchange Kinetics on Mixed Conducting Thin-Film Surfaces Investigated by In Situ Studies.
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Siebenhofer, Matthäus, Riedl, Christoph, Nenning, Andreas, Raznjevic, Sergej, Fellner, Felix, Artner, Werner, Zhang, Zaoli, Rameshan, Christoph, Fleig, Jürgen, and Kubicek, Markus
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- 2023
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18. Surface Decorations on Mixed Ionic and Electronic Conductors: Effects on Surface Potential, Defects, and the Oxygen Exchange Kinetics.
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Riedl, Christoph, Siebenhofer, Matthäus, Nenning, Andreas, Wilson, George E., Kilner, John, Rameshan, Christoph, Limbeck, Andreas, Opitz, Alexander K., Kubicek, Markus, and Fleig, Juergen
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- 2023
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19. Exo‐ and endophytic fungi enable rapid transfer of nutrients from ant waste to orchid tissue.
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Gegenbauer, Christian, Bellaire, Anke, Schintlmeister, Arno, Schmid, Markus C., Kubicek, Markus, Voglmayr, Hermann, Zotz, Gerhard, Richter, Andreas, and Mayer, Veronika E.
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SECONDARY ion mass spectrometry ,ENDOPHYTIC fungi ,ANTS ,ORCHIDS - Abstract
Summary: The epiphytic orchid Caularthron bilamellatum sacrifices its water storage tissue for nutrients from the waste of ants lodging inside its hollow pseudobulb. Here, we investigate whether fungi are involved in the rapid translocation of nutrients.Uptake was analysed with a 15N labelling experiment, subsequent isotope ratio mass spectrometry (IRMS) and secondary ion mass spectrometry (ToF‐SIMS and NanoSIMS).We encountered two hyphae types: a thick melanized type assigned to 'black fungi' (Chaetothyriales, Cladosporiales, and Mycosphaerellales) in ant waste, and a thin endophytic type belonging to Hypocreales. In few cell layers, both hyphae types co‐occurred. 15N accumulation in both hyphae types was conspicuous, while for translocation to the vessels only Hypocreales were involved. There is evidence that the occurrence of the two hyphae types results in a synergism in terms of nutrient uptake.Our study provides the first evidence that a pseudobulb (=stem)‐born endophytic network of Hypocreales is involved in the rapid translocation of nitrogen from insect‐derived waste to the vegetative and reproductive tissue of the host orchid. For C. bilamellatum that has no contact with the soil, ant waste in the hollow pseudobulbs serves as equivalent to soil in terms of nutrient sources. See also the Commentary on this article by Leroy, 238: 1752–1754. [ABSTRACT FROM AUTHOR]
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- 2023
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20. Electron beam-induced brownmillerite–perovskite phase transition in La0.6Sr0.4CoO3−δ.
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Ražnjević, Sergej, Siebenhofer, Matthäus, Bumberger, Andreas E., Böhme, Christin, Riedl, Christoph, Chen, Zhuo, Kubicek, Markus, and Zhang, Zaoli
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PHASE transitions ,ELECTRON beams ,TRANSMISSION electron microscopy ,POINT defects ,LATTICE constants ,ELECTROSTATIC interaction - Abstract
The electron beam, during high-resolution transmission electron microscopy, was employed to induce a phase transition in La
0.6 Sr0.4 CoO2.5 (LSC) from a brownmillerite ordering to an oxygen deficient perovskite structure. Prior to irradiation, a strongly alternating out-of-plane lattice parameter was observed, reflecting electrostatic interactions between AO and BO/BO2 planes in the brownmillerite ordering. During electron beam irradiation for one hour, the oxygen vacancy ordering vanished gradually, and a uniform cubic perovskite structure prevailed. To exclude beam-induced heating effects, in situ heating experiments were performed, revealing a stable brownmillerite ordering in the relevant temperature range (up to at least 500 °C). Thus, we conclude that the phase transition is caused by knock-on processes that affect oxygen vacancies in terms of a transition from structural vacancies toward extremely high concentrations of randomly distributed point defects in the ABO3 structure. [ABSTRACT FROM AUTHOR]- Published
- 2023
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21. Influence of surface atomic structure demonstrated on oxygen incorporation mechanism at a model perovskite oxide
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Riva, Michele, Kubicek, Markus, Hao, Xianfeng, Franceschi, Giada, Gerhold, Stefan, Schmid, Michael, Hutter, Herbert, Fleig, Juergen, Franchini, Cesare, Yildiz, Bilge, and Diebold, Ulrike
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- 2018
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22. Electronic and ionic effects of sulphur and other acidic adsorbates on the surface of an SOFC cathode material.
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Siebenhofer, Matthäus, Nenning, Andreas, Wilson, George E., Kilner, John A., Rameshan, Christoph, Kubicek, Markus, Fleig, Jürgen, and Blaha, Peter
- Abstract
The effects of sulphur adsorbates and other typical solid oxide fuel cell (SOFC) poisons on the electronic and ionic properties of an SrO-terminated (La,Sr)CoO
3 (LSC) surface and on its oxygen exchange kinetics have been investigated experimentally with near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), low energy ion scattering (LEIS) and impedance spectroscopy as well as computationally with density functional theory (DFT). The experiment shows that trace amounts of sulphur in measurement atmospheres form SO2− 4 adsorbates and strongly deactivate a pristine LSC surface. They induce a work function increase, indicating a changing surface potential and a surface dipole. DFT calculations reveal that the main participants in these charge transfer processes are not sub-surface transition metals, but surface oxygen atoms. The study further shows that sulphate adsorbates strongly affect oxygen vacancy formation energies in the LSC (sub-)surface, thus affecting defect concentrations and oxygen transport properties. To generalize these results, the investigation was extended to other acidic oxides which are technologically relevant as SOFC cathode poisons, such as CO2 and CrO3 . The results unveil a clear correlation of work function changes and redistributed charge with the Smith acidity of the adsorbed oxide and clarify fundamental mechanistic details of atomic surface modifications. The impact of acidic adsorbates on various aspects of the oxygen exchange reaction rate is discussed in detail. [ABSTRACT FROM AUTHOR]- Published
- 2023
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23. Unravelling the Origin of Ultra-Low Conductivity in SrTiO3 Thin Films: Sr Vacancies and Ti on A-Sites Cause Fermi Level Pinning
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Morgenbesser, Maximilian, Viernstein, Alexander, Schmid, Alexander, Herzig, Christopher, Kubicek, Markus, Taibl, Stefanie, Bimashofer, Gesara, Stahn, Jochen, Vaz, Carlos Antonio Fernandes, Döbeli, Max, Biautti, Federico, De Dios Sirvent, Juan, Liedke, Maciej Oskar, Butterling, Maik, Kamiński, Michał, Tolkiehn, Martin, Vonk, Vedran, Stierle, Andreas, Wagner, Andreas, Tarancon, Albert, Limbeck, Andreas, and Fleig, Jürgen
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Technology ,STO ,thin film characterization ,fermi level pinning ,SrTiO ,pulsed laser depositions ,site occupations ,Sr vacancies ,(3) thin films ,strontium titanate ,ultra-low conductivities ,PALS ,conductivity ,ddc:600 - Abstract
Different SrTiO3 thin films are investigated to unravel the nature of ultra-low conductivities recently found in SrTiO3 films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively-coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron-based X-ray standing wave and X-ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe-doped SrTiO3 films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo-intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (Fe-Sr and Ti-Sr) to accommodate nonstoichiometry. Sr vacancies act as mid-gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably TiSr center dot center dot\[{\rm{Ti}}_{{\rm{Sr}}}{ \bullet \bullet }\]) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self-limitation of the Ti site change and leads to a very robust pseudo-intrinsic situation, irrespective of Sr/Ti ratios and doping., Advanced Functional Materials, 32 (38), ISSN:1616-3028, ISSN:1616-301X
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- 2022
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24. In situ electrochemical observation of anisotropic lattice contraction of La0.6Sr0.4FeO3−δ electrodes during pulsed laser deposition.
- Author
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Riedl, Christoph, Siebenhofer, Matthäus, Raηnjević, Sergej, Bumberger, Andreas Ewald, Zhang, Zaoli, Limbeck, Andreas, Opitz, Alexander Karl, Kubicek, Markus, and Fleig, Jürgen
- Abstract
La
0.6 Sr0.4 FeO3−δ (LSF) electrodes were grown on different electrolyte substrates by pulsed laser deposition (PLD) and their oxygen exchange reaction (OER) resistance was tracked in real-time by in situ PLD impedance spectroscopy (i-PLD) inside the PLD chamber. This enables measurements on pristine surfaces free from any contaminations and the direct observation of thickness dependent properties. As substrates, yttria-stabilized zirconia single crystals (YSZ) were used for polycrystalline LSF growth and La0.95 Sr0.05 Ga0.95 Mg0.05 O3−δ (LSGM) single crystals or YSZ single crystals with a 5 nm buffer-layer of Gd0.2 Ce0.8 O2−δ for epitaxial LSF film growth. While polycrystalline LSF electrodes show a constant OER resistance in a broad thickness range, epitaxially grown LSF electrodes exhibit a continuous and strong increase of the OER resistance with film thickness until ≈60 nm. In addition, the activation energy of the OER resistance increases by 0.23 eV compared to polycrystalline LSF. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) measurements reveal an increasing contraction of the out-of-plane lattice parameter in the epitaxial LSF electrodes over electrode thickness. Defect thermodynamic simulations suggest that the decrease of the LSF unit cell volume is accompanied by a lowering of the oxygen vacancy concentration, explaining both the resistive increase and the increased activation energy. [ABSTRACT FROM AUTHOR]- Published
- 2023
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25. Surface Chemistry and Degradation Processes of Dense La0.6Sr0.4CoO3-δ Thin Film Electrodes.
- Author
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Siebenhofer, Matthäus, Haselmann, Ulrich, Nenning, Andreas, Friedbacher, Gernot, Bumberger, Andreas Ewald, Wurster, Stefan, Artner, Werner, Hutter, Herbert, Zaoli Zhang, Fleig, Jürgen, and Kubicek, Markus
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SURFACE chemistry ,THIN films ,SECONDARY ion mass spectrometry ,X-ray photoelectron spectroscopy ,ATOMIC force microscopy ,PARTICLE dynamics - Abstract
The changes of the surface morphology and the surface chemistry of LSC thin films grown on different substrates were tracked for 100 hours under SOFC operation conditions. Atomic force microscopy was used to monitor the formation of particles at the LSC surface. Depending on the thin film structure (polycrystalline vs. epitaxial), different particle formation dynamics were observed. Electron microscopy was employed to investigate the chemistry of the segregated particles and revealed that the particles were Srand S-rich. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy measurements were performed on degraded LSC thin films, which also found significant amounts of sulfur on the LSC surface, despite no deliberate addition of sulfur compounds, as well as A-site cation enrichment. Impedance spectroscopy was used to track the polarization resistance of LSC grown on YSZ over the same degradation period and a strong increase inthe polarization resistance and in its activation energy was revealed (1.09 to 1.73 eV). The experimental results indicate that sulfur adsorption on LSC surfaces is omnipresent in the investigated conditions and even trace amounts of sulfur compounds present in nominally pure measurement gases account for particle formation and multiple degradation effects under operating conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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26. Unravelling the Origin of Ultra‐Low Conductivity in SrTiO3 Thin Films: Sr Vacancies and Ti on A‐Sites Cause Fermi Level Pinning.
- Author
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Morgenbesser, Maximilian, Viernstein, Alexander, Schmid, Alexander, Herzig, Christopher, Kubicek, Markus, Taibl, Stefanie, Bimashofer, Gesara, Stahn, Jochen, Vaz, Carlos Antonio Fernandes, Döbeli, Max, Biautti, Federico, de Dios Sirvent, Juan, Liedke, Maciej Oskar, Butterling, Maik, Kamiński, Michał, Tolkiehn, Martin, Vonk, Vedran, Stierle, Andreas, Wagner, Andreas, and Tarancon, Albert
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POSITRON annihilation ,FERMI level ,THIN films ,PULSED laser deposition ,CHEMICAL models ,EMISSION spectroscopy ,STRONTIUM - Abstract
Different SrTiO3 thin films are investigated to unravel the nature of ultra‐low conductivities recently found in SrTiO3 films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo‐intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively‐coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron‐based X‐ray standing wave and X‐ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe‐doped SrTiO3 films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo‐intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (FeSr and TiSr) to accommodate nonstoichiometry. Sr vacancies act as mid‐gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably TiSr••\[{\rm{Ti}}_{{\rm{Sr}}}^{ \bullet \bullet }\]) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self‐limitation of the Ti site change and leads to a very robust pseudo‐intrinsic situation, irrespective of Sr/Ti ratios and doping. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
27. Thin film cathodes in SOFC research: How to identify oxygen reduction pathways?
- Author
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Opitz, Alexander K., Kubicek, Markus, Huber, Stefanie, Huber, Tobias, Holzlechner, Gerald, Hutter, Herbert, and Fleig, Jürgen
- Published
- 2013
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28. Investigating the electrochemical stability of Li7La3Zr2O12 solid electrolytes using field stress experiments
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Smetaczek, Stefan, Pycha, Eva, Ring, Joseph, Siebenhofer, Matthäus, Ganschow, Steffen, Berendts, Stefan, Nenning, Andreas, Kubicek, Markus, Rettenwander, Daniel, Limbeck, Andreas, and Fleig, Jürgen
- Subjects
Chemistry - Abstract
Cubic Li7La3Zr2O12 (LLZO) garnets are among the most promising solid electrolytes for solid-state batteries with the potential to exceed conventional battery concepts in terms of energy density and safety. The electrochemical stability of LLZO is crucial for its application, however, controversial reports in the literature show that it is still an unsettled matter. Here, we investigate the electrochemical stability of LLZO single crystals by applying electric field stress via macro- and microscopic ionically blocking Au electrodes in ambient air. Induced material changes are subsequently probed using various locally resolved analysis techniques, including microelectrode electrochemical impedance spectroscopy (EIS), laser induced breakdown spectroscopy (LIBS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and microfocus X-ray diffraction (XRD). Our experiments indicate that LLZO decomposes at 4.1–4.3 V vs. Li+/Li, leading to the formation of Li-poor phases like La2Zr2O7 beneath the positively polarized electrode. The reaction is still on-going even after several days of polarization, indicating that no blocking interfacial layer is formed. The decomposition can be observed at elevated as well as room temperature and suggests that LLZO is truly not compatible with high voltage cathode materials., The combination of field stress experiments with subsequent electrochemical, chemical, and structural analysis provides insight into the stability window and decomposition behavior of LLZO.
- Published
- 2021
29. Formation and Detection of High-Pressure Oxygen in Closed Pores of La0.6Sr0.4CoO3−δ Solid Oxide Electrolysis Anodes.
- Author
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Krammer, Martin, Schmid, Alexander, Siebenhofer, Matthäus, Bumberger, Andreas Ewald, Herzig, Christopher, Limbeck, Andreas, Kubicek, Markus, and Fleig, Juergen
- Published
- 2022
- Full Text
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30. In situ techniques reveal the true capabilities of SOFC cathode materials and their sudden degradation due to omnipresent sulfur trace impurities.
- Author
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Riedl, Christoph, Siebenhofer, Matthäus, Nenning, Andreas, Schmid, Alexander, Weiss, Maximilian, Rameshan, Christoph, Limbeck, Andreas, Kubicek, Markus, Opitz, Alexander Karl, and Fleig, Juergen
- Abstract
In this study, five different mixed conducting cathode materials were grown as dense thin films by pulsed laser deposition (PLD) and characterized via in situ impedance spectroscopy directly after growth inside the PLD chamber (i-PLD). This technique enables quantification of the oxygen reduction kinetics on pristine and contaminant-free mixed conducting surfaces. The measurements reveal excellent catalytic performance of all pristine materials with polarization resistances being up to two orders of magnitude lower than those previously reported in the literature. For instance, on dense La
0.6 Sr0.4 CoO3−δ thin films, an area specific surface resistance of ∼0.2 Ω cm2 at 600 °C in synthetic air was found, while values usually >1 Ω cm2 are measured in conventional ex situ measurement setups. While surfaces after i-PLD measurements were very clean, ambient pressure X-ray photoelectron spectroscopy (AP-XPS) measurements found that all samples measured in other setups were contaminated with sulfate adsorbates. In situ impedance spectroscopy during AP-XPS revealed that already trace amounts of sulfur present in high purity gases accumulate quickly on pristine surfaces and lead to strongly increased surface polarization resistances, even before the formation of a SrSO4 secondary phase. Accordingly, the inherent excellent catalytic properties of this important class of materials were often inaccessible so far. As a proof of concept, the fast kinetics observed on sulfate-free surfaces were also realized in ex situ measurements with a gas purification setup and further reduces the sulfur concentration in the high purity gas. [ABSTRACT FROM AUTHOR]- Published
- 2022
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31. A mechanism of AP-1 suppression through interaction of c-Fos with lamin A/C
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Ivorra, Carmen, Kubicek, Markus, Gonzalez, Jose M., Sanz-Gonzalez, Silvia M., Alvarez-Barrientos, Alberto, O'Connor, Jose-Enrique, Burke, Brian, and Andres, Vicente
- Subjects
Cell cycle -- Research ,Genetic transcription -- Research ,Proteins -- Chemical properties ,Biological sciences - Abstract
A study was conducted to show that the intermediate filament protein lamin A/C suppresses AP-1 function through direct interaction with c-Fos, and that both proteins could interact and colocalize at the nuclear envelope (NE) in mammalian cells. The results indicated that lamin A/C-mediated c-Fos sequestration at the NE as a novel mechanism of transcriptional and cell cycle control.
- Published
- 2006
32. Performance modulation through selective, homogenous surface doping of lanthanum strontium ferrite electrodes revealed by in situ PLD impedance measurements.
- Author
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Riedl, Christoph, Siebenhofer, Matthäus, Nenning, Andreas, Friedbacher, Gernot, Weiss, Maximilian, Rameshan, Christoph, Bernardi, Johannes, Limbeck, Andreas, Kubicek, Markus, Opitz, Alexander Karl, and Fleig, Juergen
- Abstract
Accelerating the oxygen reduction kinetics of solid oxide fuel cell (SOFC) cathodes is crucial to improve their efficiency and thus to provide the basis for an economically feasible application of intermediate temperature SOFCs. In this work, minor amounts of Pt were doped into lanthanum strontium ferrite (LSF) thin film electrodes to modulate the material's oxygen exchange performance. Surprisingly, Pt was found to be incorporated on the B-site of the perovskite electrode as non metallic Pt
4+ . The polarization resistance of LSF thin film electrodes with and without additional Pt surface doping was compared directly after film growth employing in situ electrochemical impedance spectroscopy inside a PLD chamber (i-PLD). This technique enables observation of the polarization resistance of pristine electrodes unaltered by degradation or any external contamination of the electrode surface. Moreover, growth of multi-layers of materials with different compositions on the very same single crystalline electrolyte substrate combined with in situ impedance measurements allow excellent comparability of different materials. Even a 5 nm layer of Pt doped LSF (1.5 at% Pt), i.e. a Pt loading of 80 ng cm−2 , improved the polarization resistance by a factor of about 2.5. In addition, p(O2 ) and temperature dependent impedance measurements on both pure and Pt doped LSF were performed in situ and obtained similar activation energies and p(O2 ) dependence of the polarization resistance, which allow us to make far reaching mechanistic conclusions indicating that Pt4+ introduces additional active sites. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
33. Investigating oxygen reduction pathways on pristine SOFC cathode surfaces by in situ PLD impedance spectroscopy.
- Author
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Siebenhofer, Matthäus, Riedl, Christoph, Schmid, Alexander, Limbeck, Andreas, Opitz, Alexander Karl, Fleig, Jürgen, and Kubicek, Markus
- Abstract
The oxygen exchange reaction mechanism on truly pristine surfaces of SOFC cathode materials (La
0.6 Sr0.4 CoO3−δ = LSC, La0.6 Sr0.4 FeO3−δ = LSF, (La0.6 Sr0.4 )0.98 Pt0.02 FeO3−δ = Pt:LSF, SrTi0.3 Fe0.7 O3−δ = STF, Pr0.1 Ce0.9 O2−δ = PCO and La0.6 Sr0.4 MnO3−δ = LSM) was investigated employing in situ impedance spectroscopy during pulsed laser deposition (i-PLD) over a wide temperature and p(O2 ) range. Besides demonstrating the often astonishing catalytic capabilities of the materials, it is possible to discuss the oxygen exchange reaction mechanism based on experiments on clean surfaces unaltered by external degradation processes. All investigated materials with at least moderate ionic conductivity (i.e. all except LSM) exhibit polarization resistances with very similar p(O2 )- and T-dependences, mostly differing only in absolute value. In combination with non-equilibrium measurements under polarization and defect chemical model calculations, these results elucidate several aspects of the oxygen exchange reaction mechanism and refine the understanding of the role oxygen vacancies and electronic charge carriers play in the oxygen exchange reaction. It was found that a major part of the effective activation energy of the surface exchange reaction, which is observed during equilibrium measurements, originates from thermally activated charge carrier concentrations. Electrode polarization was therefore used to control defect concentrations and to extract concentration amended activation energies, which prove to be drastically different for oxygen incorporation and evolution (0.26 vs. 2.05 eV for LSF). [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
34. Approaching clinical proteomics: current state and future fields of application in fluid proteomics
- Author
-
Apweiler, Rolf, Aslanidis, Charalampos, Deufel, Thomas, Gerstner, Andreas, Hansen, Jens, Hochstrasser, Dennis, Kellner, Roland, Kubicek, Markus, Lottspeich, Friedrich, Maser, Edmund, Mewes, Hans-Werner, Meyer, Helmut E., Müllner, Stefan, Mutter, Wolfgang, Neumaier, Michael, Nollau, Peter, Nothwang, Hans G., Ponten, Fredrik, Radbruch, Andreas, Reinert, Knut, Rothe, Gregor, Stockinger, Hannes, Tarnok, Attila, Taussig, Mike J., Thiel, Andreas, Thiery, Joachim, Ueffing, Marius, Valet, Günther, Vandekerckhove, Joel, Verhuven, Wiltrud, Wagener, Christoph, Wagner, Oswald, and Schmitz, Gerd
- Published
- 2009
- Full Text
- View/download PDF
35. Cation non-stoichiometry in Fe:SrTiO3 thin films and its effect on the electrical conductivity.
- Author
-
Morgenbesser, Maximilian, Taibl, Stefanie, Kubicek, Markus, Schmid, Alexander, Viernstein, Alexander, Bodenmüller, Niklas, Herzig, Christopher, Baiutti, Federico, de Dios Sirvent, Juan, Liedke, Maciej Oskar, Butterling, Maik, Wagner, Andreas, Artner, Werner, Limbeck, Andreas, Tarancon, Albert, and Fleig, Jürgen
- Published
- 2021
- Full Text
- View/download PDF
36. Experimental approaches for monitoring defect chemical changes in Fe-doped SrTiO3 caused by UV irradiation
- Author
-
Viernstein, Alexander, Kubicek, Markus, Morgenbesser, Maximilian, Huber, Tobias, Ellmeyer, Emil, and Fleig, Jürgen
- Subjects
UV/VIS spectroscopy ,Fe doped SrTiO3 ,GaPO4 microbalance ,inplane conductivity ,photochromism - Abstract
The defect chemistry in the mid-band gap semiconductor SrTiO3 (STO) plays a crucial role for its properties. These can be tuned by temperature, doping, p(O2), and UV irradiation. Since UV exposure leads to the formation of photoelectrons and –holes the oxygen chemical potential of oxygen is changed. This results in an enhanced incorporation of oxygen into Fe-doped STO at elevated temperatures. In this work different approaches to investigate this phenomena are introduced. i) Oxygen compositional changes can be probed by measuring the light induced weight change using GaPO4 microbalances. ii) UV exposure and oxygen incorporation also cause a photo and a battery voltage, which can be measured in-situ. iii) Inplane conductivity measurements reveal an increase of the electron hole conductivity, as the result of Fe3+ oxidation to Fe4+. iv) This change of the Fe oxidation state additionally leads to a change in the color of Fe-doped STO from brownish/transparent to black. Two broad additional absorption bands in the region of 440 nm and 590 nm occur.
- Published
- 2019
- Full Text
- View/download PDF
37. UV induced photochromism in Fe-doped SrTiO3 caused by oxygen stoichiometry changes
- Author
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Viernstein, Alexander, Kubicek, Markus, Morgenbesser, Maximilian, Walch, Gregor, Brunauer, Georg, and Fleig, Jürgen
- Subjects
Fe doped SrTiO3 ,inplane conductivity ,high temperature photochromism ,oxygen incorporation - Abstract
In the last decades Fe-doped SrTiO3 (Fe:STO) has become one of the best investigated mixed conducting materials. Nevertheless, the effect of UV irradiation at elevated temperatures on the material’s composition, more precisely on its oxygen content, has hardly been examined so far. UV illumination in oxygen causes an enhanced oxygen incorporation rate and therefore a decreased oxygen vacancy concentration of SrTiO3. Consequently, Fe3+ in Fe:STO is oxidized to Fe4+ to preserve charge neutrality. This oxidation may cause color changes in Fe:STO and a decline in the AC and DC resistivity, which can be investigated by UV/VIS spectroscopy, inplane impedance spectroscopy, van der Pauw measurements respectively. Oxygen can also be released again from Fe:STO by annealing without UV exposure. Therefore, reversibly switching between these described states can be obtained.
- Published
- 2019
- Full Text
- View/download PDF
38. High‐Temperature Photochromism of Fe‐Doped SrTiO3 Caused by UV‐Induced Bulk Stoichiometry Changes
- Author
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Viernstein, Alexander, Kubicek, Markus, Morgenbesser, Maximilian, Walch, Gregor, Brunauer, Georg Christoph, and Fleig, Jürgen
- Subjects
UV/VIS spectroscopy ,Fe doped SrTiO3 ,electrochemical impedance spectroscopy ,UV-induced oxygen incorporation ,high temperature photochromism - Abstract
The impact of UV irradiation on Fe‐doped SrTiO3 (Fe:STO) single crystals is investigated at elevated temperatures. Illumination leads to incorporation of oxygen into the single crystals and thus to a decreasing oxygen vacancy concentration and oxidation of Fe3+ to Fe4+. The Fe4+ ions cause a color change from transparent/brownish to black. This photochromic blackening due to stoichiometry changes at elevated temperatures is irreversible at room temperature, but annealing at high temperatures, for example at 700 °C, can restore the original stoichiometry and color. Absorbance changes due to UV irradiation are monitored by ex situ and in situ UV/VIS spectroscopy experiments and changes in electrical properties are measured by van der Pauw measurements and in‐plane electrochemical impedance spectroscopy. After 1140 min of illumination at 440 °C, for example, electrical measurements reveal a conductivity increase by more than a factor of 5 due to the enhanced hole concentration in blackened Fe:STO. In addition, UV illumination increases the oxygen chemical potential up to a calculated p(O2) of more than 109 Pa in Fe:STO. Hence, UV light can be used to tune the color, but also electrical properties of Fe:STO by directly impacting the bulk defect concentrations.
- Published
- 2019
39. Operando X-ray investigation of electrode/electrolyte interfaces in model solid oxide fuel cells
- Author
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Volkov, Sergey, Vonk, Vedran, Khorshidi, Navid, Franz, Dirk, Kubicek, Markus, Kilic, Volkan, Felici, Roberto, Huber, Tobias M., Navickas, Edvinas, Rupp, Ghislain M., Fleig, Juergen, Stierle, Andreas, Deutsches Elektronen-Synchrotron [Hamburg] (DESY), Univ Hamburg, Fachbereich Phys, Jungiusstr 9, D-20355 Hamburg, Germany, Max Planck Institute for Intelligent Systems, Max-Planck-Gesellschaft, Vienna Univ Technol, Inst Chem Technol & Analyt, Getreidemarkt 9, A-1060 Vienna, Austria, Univ Siegen, D-57072 Siegen, Germany, and European Synchrotron Radiation Facility (ESRF)
- Subjects
ddc:540 ,[CHIM]Chemical Sciences ,Article - Abstract
International audience; We employed operando anomalous surface X-ray diffraction to investigate the buried interface between the cathode and the electrolyte of a model solid oxide fuel cell with atomic resolution. The cell was studied under different oxygen pressures at elevated temperatures and polarizations by external potential control. Making use of anomalous X-ray diffraction effects at the Y and Zr K-edges allowed us to resolve the interfacial structure and chemical composition of a (100)-oriented, 9.5 mol % yttria-stabilized zirconia (YSZ) single crystal electrolyte below a La0.6Sr0.4CoO3-delta (LSC) electrode. We observe yttrium segregation toward the YSZ/LSC electrolyte/electrode interface under reducing conditions. Under oxidizing conditions, the interface becomes Y depleted. The yttrium segregation is corroborated by an enhanced outward relaxation of the YSZ interfacial metal ion as layer. At the same time, an increase in point defect concentration in the electrolyte at the interface was observed, as evidenced by reduced YSZ crystallographic site occupancies for the cations as well as the oxygen ions. Such changes in composition are expected to strongly influence the oxygen ion transport through this interface which plays an important role for the performance of solid oxide fuel cells. The structure of the interface is compared to the bare YSZ(100) surface structure near the microelectrode under identical conditions and to the structure of the YSZ(100) surface prepared under ultrahigh vacuum conditions
- Published
- 2016
40. Investigating the electrochemical stability of Li7La3Zr2O12 solid electrolytes using field stress experiments.
- Author
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Smetaczek, Stefan, Pycha, Eva, Ring, Joseph, Siebenhofer, Matthäus, Ganschow, Steffen, Berendts, Stefan, Nenning, Andreas, Kubicek, Markus, Rettenwander, Daniel, Limbeck, Andreas, and Fleig, Jürgen
- Abstract
Cubic Li
7 La3 Zr2 O12 (LLZO) garnets are among the most promising solid electrolytes for solid-state batteries with the potential to exceed conventional battery concepts in terms of energy density and safety. The electrochemical stability of LLZO is crucial for its application, however, controversial reports in the literature show that it is still an unsettled matter. Here, we investigate the electrochemical stability of LLZO single crystals by applying electric field stress via macro- and microscopic ionically blocking Au electrodes in ambient air. Induced material changes are subsequently probed using various locally resolved analysis techniques, including microelectrode electrochemical impedance spectroscopy (EIS), laser induced breakdown spectroscopy (LIBS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and microfocus X-ray diffraction (XRD). Our experiments indicate that LLZO decomposes at 4.1–4.3 V vs. Li+ /Li, leading to the formation of Li-poor phases like La2 Zr2 O7 beneath the positively polarized electrode. The reaction is still on-going even after several days of polarization, indicating that no blocking interfacial layer is formed. The decomposition can be observed at elevated as well as room temperature and suggests that LLZO is truly not compatible with high voltage cathode materials. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
41. The Chemical Evolution of the La[subscript 0.6]Sr[subscript 0.4]CoO[subscript 3−δ] Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity
- Author
-
Opitz, Alexander K, Rameshan, Christoph, Kubicek, Markus, Rupp, Ghislain M, Götsch, Thomas, Blume, Raoul, Hävecker, Michael, Knop-Gericke, Axel, Rupprechter, Günther, Klötzer, Bernhard, Fleig, Jürgen, Opitz, Alexander K., Rupp, Ghislain M., Nenning, Andreas, Massachusetts Institute of Technology. Department of Materials Science and Engineering, and Nenning, Andreas
- Subjects
sense organs - Abstract
Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO₃ (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O₂ reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC. Keywords: Oxygen reduction; SOFC cathode; Strontium segregation; NAP-XPS; Impedance spectroscopy; Perovskite-type electrode
- Published
- 2018
42. High Oxygen Exchange Activity of Pristine La0.6Sr0.4FeO3–δFilms and Its Degradation.
- Author
-
Schmid, Alexander, Nenning, Andreas, Opitz, Alexander, Kubicek, Markus, and Fleig, Jürgen
- Subjects
EXCHANGE reactions ,THIN films ,IMPEDANCE spectroscopy ,OXYGEN ,EXCHANGE - Abstract
The polarization resistance of La
0.6 Sr0.4 FeO3–δ (LSF) thin film electrodes was investigated by electrochemical impedance spectroscopy. Different states were considered, ranging from pristine films right after deposition to films degraded under various conditions. Impedance measurements performed inside the pulsed laser deposition chamber (in-situ) revealed the existence of a very facile, low resistive state of as-deposited thin films with up to two orders of magnitude lower resistances compared to conventional ex-situ measurements and literature data. Ex-situ and in-situ measurements show different pO2 dependencies of polarization resistances, suggesting a different oxygen exchange reaction mechanism on the as-deposited films. The time dependence of the polarization resistance indicates that two degradation mechanisms with different timescales are responsible for the much higher resistances found in ex-situ measurements. Degradation mechanisms are discussed and conclusions with respect to the rate determining step of oxygen exchange on different surfaces are drawn. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
43. Oxygen exchange kinetics and nonstoichiometry of pristine La0.6Sr0.4CoO3−δ thin films unaltered by degradation.
- Author
-
Siebenhofer, Matthäus, Huber, Tobias Martin, Friedbacher, Gernot, Artner, Werner, Fleig, Jürgen, and Kubicek, Markus
- Abstract
La
0.6 Sr0.4 CoO3−δ thin films grown on YSZ single crystals were investigated directly in the stage of deposition by means of in situ impedance spectroscopy during pulsed laser deposition (IPLD). This method allows the observation of dense thin films unaltered by degradation and provides information about the oxygen exchange kinetics as well as the defect chemistry of pristine LSC thin films. These measurements revealed remarkably low surface resistance values (1.3 Ω cm2 at 600 °C and 0.04 mbar O2 ) compared to films measured outside the PLD chamber (∼20 Ω cm2 at 600 °C and 0.04 mbar O2 ). Also the activation energy of the surface exchange resistance at 0.04 mbar p(O2 ) is significantly lower than at ambient conditions (∼1 eV vs. ∼1.3 eV) and degradation happens considerably slower. Furthermore, the grain size of the LSC thin film does not affect its initial surface resistance directly after deposition. The chemical capacitance of LSC thin films was linked to the concentration of oxygen vacancies and shows that LSC thin films exhibit lower oxygen vacancy concentrations than the corresponding bulk material. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
44. Study of metabolism and identification of productive regions in filamentous fungi via spatially resolved time-of-flight secondary ion mass spectrometry.
- Author
-
Veiter, Lukas, Kubicek, Markus, Hutter, Herbert, Pittenauer, Ernst, Herwig, Christoph, and Slouka, Christoph
- Subjects
- *
SECONDARY ion mass spectrometry , *FILAMENTOUS fungi , *TIME-of-flight mass spectrometry , *PENICILLIUM chrysogenum , *MANUFACTURING processes - Abstract
Filamentous fungi are well-established production hosts that feature a strong interconnection between morphology, physiology, and productivity. For penicillin production in Penicillium chrysogenum, industrial processes frequently favor a pellet morphology comprising compact hyphal agglomerates. Inherently these tightly packed entanglements lead to inactive, degrading sections within the pellet's core because of limitations. Optimal process design requires detailed knowledge of the nature of the limitations and localization of productive zones in the biomass, which is generally obtainable through modeling and complex analytical methods such as oxygen microelectrode and histological investigations. Methods that combine physiological and morphological insight are crucial yet scarce for filamentous fungi. In this study, we used time-of-flight secondary ion mass spectrometry in combination with oxygen and glucose tracer substrates, requiring little effort for sample preparation and measurement. Our method is capable of analyzing oxygen and substrate uptake in various morphological structures by the use of 18O as a tracer. In parallel, we can assess productive biomass regions through identification of penicillin mass fragments to simultaneously study oxygen diffusion, substrate incorporation, and productive biomass sections. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
45. Perovskite La0.6Sr0.4Cr1-xCoxO3-δ Solid Solutions for Solar-Thermochemical Fuel Production: Strategies to Lower the Operation Temperature
- Author
-
Bork, Alexander H., Kubicek, Markus, Struzik, Michal, and Rupp, Jennifer L.M.
- Abstract
Storing abundant solar energy in synthetic fuels is key to ensure a sustainable energy future by replacing fossil fuels and reducing global warming emissions. Practical implementation of the solar-to-fuel technology is predicated on finding new materials with higher efficiency and lower operation temperature than state-of-the-art materials. We use criteria aimed for designing such efficient solar-to-fuel conversion materials in the perovskite system. Based on thermodynamic considerations, the first perovskite solute–solution series, La0.6Sr0.4Cr1−xCoxO3−δ, is investigated to gain fundamental understanding on the role of B-site cationic doping in water and CO2 splitting to produce synthetic fuel. Notably, all of the novel material compositions operate in a strongly lowered temperature regime of 800–1200 °C compared to state-of-the-art binary oxides in the field. We found an optimum in doping for fuel production performance, namely La0.6Sr0.4Cr0.8Co0.2O3−δ, which viably splits both CO2 and H2O. Based on thermogravimetric analysis, we show that the highest performing perovskite splits 25 times more CO2 compared to the current state-of-the-art material, ceria, for two-step thermochemical cycling at 800–1200 °C. No adverse formation of carbonates in a CO2 atmosphere or cation segregation was observed in near and long range structural investigations, which highlight the durability and potential of these solid solutions. These new perovskite compositions enable lowering of the standard solar-to-fuel reactor temperature by 300 °C. The lowered operating temperature has tremendous implications for solar-synthesized fuels in a reactor in terms of lowered heat loss, increased efficiency, and reactor materials., Journal of Materials Chemistry A, 3 (30), ISSN:2050-7488, ISSN:2050-7496
- Published
- 2015
- Full Text
- View/download PDF
46. The Chemical Evolution of the La0.6Sr0.4CoO3−δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity.
- Author
-
Opitz, Alexander K., Rameshan, Christoph, Kubicek, Markus, Rupp, Ghislain M., Nenning, Andreas, Götsch, Thomas, Blume, Raoul, Hävecker, Michael, Knop-Gericke, Axel, Rupprechter, Günther, Klötzer, Bernhard, and Fleig, Jürgen
- Subjects
ELECTROCHEMICAL analysis ,OXIDATION-reduction reaction ,SOLID oxide fuel cells ,STOICHIOMETRY ,ELECTROLYSIS - Abstract
Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO
3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
47. Interfacial Degradation Processes in Solid-State Batteries during High Temperature Processing and the Mitigation Strategies.
- Author
-
Mehraj Ud Din, Mir, Ladenstein, Lukas, Ring, Joseph, Knez, Daniel, Smetazcek, Stefan, Kubicek, Markus, Sadeqi-Moqadam, Mohsen, Kothleitner, Gerald, Limbeck, Andreas, Fleig, Jürgen, Redhammer, Günther, and Rettenwander, Daniel
- Published
- 2023
- Full Text
- View/download PDF
48. Correlating surface cation composition and thin film microstructure with the electrochemical performance of lanthanum strontium cobaltite (LSC) electrodes
- Author
-
Rupp, Ghislain M., Limbeck, Andreas, Kubicek, Markus, Penn, Alexander, Stöger-Pollach, Michael, Friedbacher, Gernot, and Fleig, Jürgen
- Subjects
620: Ingenieurwissenschaften ,Chemie [540] ,ddc:540 ,Ingenieurwissenschaften [620] ,ddc:620 ,540: Chemie - Abstract
La0.6Sr0.4CoO3-δ thin films of varying thicknesses (20-170 nm) were prepared by pulsed laser deposition on yttria-stabilized zirconia (100) substrates, and their electrochemical electrode performance was correlated with the chemical surface composition and microstructure (e.g. porosity, surface area). The surface cation composition was analyzed by an atomic etching procedure with on-line inductively coupled plasma optical emission spectrometry detection. The surface sensitivity of the method was increased by dynamically switching the etching reagent during the on-line analysis and quantitative results for even the top atomic layer were obtained. A water-soluble Sr-rich surface species could be quantified on top of the LSC films and in combination with electrochemical analysis of the films by impedance spectroscopy an improved understanding of the surface exchange resistance could be obtained. Microstructural features such as the effective porosity of the films became accessible by a combination of these methods.
- Published
- 2014
- Full Text
- View/download PDF
49. Cation diffusion in La₀.₆Sr₀.₄CoO 3 - δ below 800 °C and its relevance for Sr segregation
- Author
-
Kubicek, Markus, Rupp, Ghislain M., Huber, Stefanie, Penn, Alexander, Opitz, Alexander K., Bernardi, Johannes, Stöger-Pollach, Michael, Hutter, Herbert, and Fleig, Jürgen
- Subjects
Chemie [540] ,ddc:540 ,Ingenieurwissenschaften [620] ,ddc:620 - Abstract
Cation diffusion was investigated in la₀.₆Sr₀.₄CoO 3 - δ (LSC) thin films on (100) yttria stabilized zirconia in the temperature range 625-800 °C. Isotopic ( 86Sr) and elemental tracers (Fe, Sm) were used to establish diffusion profiles of the cations in bi- and multi-layered thin films. The profiles were analyzed by time of flight-secondary ion mass spectrometry (ToF-SIMS). Grain and grain boundary diffusion coefficients of the cations were determined for LSC thin films with columnar grains-diffusion along grain boundaries is shown to be about three orders of magnitude faster than in grains. This could be verified for thin films with different grain size. A- and B-site cations showed very similar temperature dependencies with activation energies of ∼3.5 eV for bulk and ∼4.1 eV for grain boundary diffusion. The importance of cation diffusivities for surface segregation of Sr and thus for a major degradation mechanism of LSC cathodes in solid oxide fuel cells is discussed.
- Published
- 2013
50. Bulk and surface characterization of In2O3(001) single crystals
- Author
-
Hagleitner, Daniel R., Menhart, Manfred, Jacobson, Peter, Blomberg, Sara, Schulte, Karina, Lundgren, Edvin, Kubicek, Markus, Fleig, Juergen, Kubel, Frank, Puls, Christoph, Limbeck, Andreas, Hutter, Herbert, Boatner, Lynn A., Schmid, Michael, and Diebold, Ulrike
- Subjects
Atom and Molecular Physics and Optics ,Physical Sciences ,Natural Sciences - Abstract
A comprehensive bulk and surface investigation of high-quality In2O3(001) single crystals is reported. The transparent-yellow, cube-shaped single crystals were grown using the flux method. Inductively coupled plasma mass spectrometry (ICP-MS) reveals small residues of Pb, Mg, and Pt in the crystals. Four-point-probe measurements show a resistivity of 2.0 +/- 0.5 x 10(5) Omega cm, which translates into a carrier concentration of approximate to 10(12) cm(-3). The results from x-ray diffraction (XRD) measurements revise the lattice constant to 10.1150(5) angstrom from the previously accepted value of 10.117 angstrom. Scanning tunneling microscopy (STM) images of a reduced (sputtered/annealed) and oxidized (exposure to atomic oxygen at 300 degrees C) surface show a step height of 5 angstrom, which indicates a preference for one type of surface termination. The surfaces stay flat without any evidence for macroscopic faceting under any of these preparation conditions. A combination of low-energy ion scattering (LEIS) and atomically resolved STM indicates an indium-terminated surface with small islands of 2.5 angstrom height under reducing conditions, with a surface structure corresponding to a strongly distorted indium lattice. Scanning tunneling spectroscopy (STS) reveals a pronounced surface state at the Fermi level (E-F). Photoelectron spectroscopy (PES) shows additional, deep-lying band gap states, which can be removed by exposure of the surface to atomic oxygen. Oxidation also results in a shoulder at the O 1s core level at a higher binding energy, possibly indicative of a surface peroxide species. A downward band bending of 0.4 eV is observed for the reduced surface, while the band bending of the oxidized surface is of the order of 0.1 eV or less.
- Published
- 2012
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