| 1. |
- Mazzei, Laura, 1988, et al.
(författare)
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Local Coordination of Protons in In- and Sc-Doped BaZrO3
- 2019
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:43, s. 26065-26072
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Tidskriftsartikel (refereegranskat)abstract
- Acceptor-doped barium zirconate-based proton conductors are currently receiving considerable attention because of their promise as electrolytes in future electrochemical devices, such as solid oxide fuel cells, but the defect chemistry, especially in regard to the local coordination environment and dynamics of protons in these materials, is unclear. Here, we investigate the local coordination environments and vibrational dynamics of protons in samples of the proton conducting material BaZr1-xMxO3Hx with M = In and Sc, and x = 0.1 and 0.5, using inelastic neutron scattering (INS), infrared (IR), and Raman spectroscopy together with ab initio molecular dynamics (AIMD) simulations. The local coordination of protons is shown to exhibit a rather peculiar dependence on the type and concentration of dopant atoms, as they are found to be similar for BaZr1-xScxO3Hx with x = 0.1 and 0.5 and BaZr1-xInxO3Hx with x = 0.1, whereas for BaZr1-xInxO3Hx with x = 0.5 additional proton sites seem to be present. It is argued that these additional proton sites are characterized by local structural arrangements reminiscent of the fully In-substituted material BaInO3H. The presence of these local structural arrangements points toward different local proton mobilities between BaZr1-xInxO3Hx with x = 0.5 and the other three materials and a higher rate of proton transfer events in brownrnillerite-type local structures.
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| 2. |
- Mazzei, Laura, 1988, et al.
(författare)
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Local structure and vibrational dynamics in indium-doped barium zirconate
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7:13, s. 7360-7372
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Tidskriftsartikel (refereegranskat)abstract
- Barium zirconate (BaZrO3), when substituted with trivalent acceptor ions to replace Zr4+, is a proton conducting material of interest for several electrochemical applications. The local coordination environments, and vibrational dynamics, of the protons are known to critically influence the material's proton conducting properties, however, the nature of the static and dynamic structure around the protons and, especially, how it is affected by the dopant atoms for high doping concentrations, remains to be elucidated. Here we report results from X-ray powder diffraction, infrared (IR) spectroscopy, inelastic neutron scattering (INS) and ab initio molecular dynamics (AIMD) simulations on a hydrated sample of BaZrO3 substituted with 50% In3+. The investigation of the momentum-transfer (Q) dependence of the INS spectrum is used to aid the analysis of the spectra and the assignment of the spectral components to fundamental O-H bend and O-H stretch modes and higher-order transitions. The AIMD simulations show that the INS spectrum is constituted of the overlapping spectra of protons in several different local structural environments, whereas the local proton environments for specific protons are found to vary with time as a result of thermally activated vibrations of the perovskite lattice. It is argued that, converse to more weakly doped systems, such as 20% Y-doped BaZrO3, the dopant-proton association effect does not hinder the diffusion of protons due to the presence of percolation paths of dopant atoms throughout the perovskite lattice.
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| 3. |
- Perrichon, Adrien, 1988, et al.
(författare)
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Local structure and vibrational dynamics of proton conducting Ba2In2O5(H2O)x
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7:29, s. 17626-17636
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Tidskriftsartikel (refereegranskat)abstract
- We study the local structure and vibrational dynamics of the brownmillerite-based proton conductors Ba2In2O5(H2O)x, with x = 0.30, 0.76, and 0.92, using infrared spectroscopy, inelastic neutron scattering and ab initio molecular dynamics simulations. Ba2In2O5(H2O)x is found to exhibit two main types of proton sites, H(1) and H(2). The H(1) site is characterised by the coexistence of two intra-octahedral hydrogen-bond geometries, whereas the H(2) site is characterised by inter-octahedral hydrogen bonding. While the strength of the hydrogen bonding is similar for the majority of protons in the two proton sites, ≈10% of the H(2) protons forms unusually strong hydrogen bonds due to local proton environments characterised by an unusually short oxygen-oxygen separation distance of ≈2.6 Å. These local proton environments are manifested as two O-H stretch bands in the infrared absorbance spectra, at 255 and 290 meV, respectively. These O-H stretch bands are as well observed in the related class of In-doped perovskite-type oxides, BaInyZr1-yO3-y/2 (0.25 ≤ y ≤ 0.75), suggesting that these perovskites may display brownmillerite-like distortions on a local length scale. In effect, these results point towards a clustering of the In atoms in these perovskite materials. Further, the infrared spectra of Ba2In2O5(H2O)x show a minor evolution as a function of x, because the protons tend to segregate into oxygen-rich hydrogen-rich domains upon dehydration. This points towards a highly anisotropic proton conduction mechanism in partially hydrated phases. This insight motivates efforts to identify ways to avoid phase separation, perhaps by suitable cation substitutions, as a route to accommodate high proton conductivity.
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| 4. |
- Bielecki, Johan, et al.
(författare)
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Structure and dehydration mechanism of the proton conducting oxide Ba2In2O5(H2O)(x)
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:4, s. 1224-1232
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Tidskriftsartikel (refereegranskat)abstract
- The structure and dehydration mechanism of the proton conducting oxide Ba2In2O5(H2O)(x) are investigated by means of variable temperature (20-600 degrees C) Raman spectroscopy together with thermal gravimetric analysis and inelastic neutron scattering. At room temperature, Ba2In2O5(H2O)(x) is found to be fully hydrated (x = 1) and to have a perovskite-like structure, which dehydrates gradually with increasing temperature and at around 600 degrees C the material is essentially dehydrated (x approximate to 0.2). The dehydrated material exhibits a brownmillerite structure, which is featured by alternating layers of InO6 octahedra and InO4 tetrahedra. The transition from a perovskite-like to a brownmillerite-like structure upon increasing temperature occurs through the formation of an intermediate phase at ca. 370 degrees C, corresponding to a hydration degree of approximately 50%. The structure of the intermediate phase is similar to the structure of the dehydrated material, but with the difference that it exhibits a non-centrosymmetric distortion of the InO6 octahedra that is not present in the dehydrated material. The dehydration process upon heating is a two-stage mechanism; for temperatures below the hydrated-to-intermediate phase transition, dehydration is characterized by a homogenous release of protons over the entire oxide lattice, whereas above the transition a preferential desorption of protons originating in the nominally tetrahedral layers is observed. Furthermore, our spectroscopic results point towards the co-existence of two structural phases, which relate to the two lowest-energy proton configurations in the material. The relative contributions of the two proton configurations depend on how the sample is hydrated.
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| 5. |
- Eklöf-Österberg, Carin, 1987, et al.
(författare)
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The role of oxygen vacancies on the vibrational motions of hydride ions in the oxyhydride of barium titanate
- 2020
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 8:13, s. 6360-6371
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type oxyhydrides, BaTiO3-xHx, represent a novel class of hydride ion conducting materials of interest for several electrochemical applications, but fundamental questions surrounding the defect chemistry and hydride ion transport mechanism remain unclear. Here we report results from powder X-ray diffraction, thermal gravimetric analysis, nuclear magnetic resonance spectroscopy, inelastic neutron scattering (INS), and density functional theory (DFT) simulations on three metal hydride reduced BaTiO3 samples characterized by the simultaneous presence of hydride ions and oxygen vacancies. The INS spectra are characterized by two predominating bands at around 114 (omega(perpendicular to)) and 128 (omega(parallel to)) meV, assigned as fundamental Ti-H vibrational modes perpendicular and parallel to the Ti-H-Ti bond direction, respectively, and four additional, weaker, bands at around 99 (omega(1)), 110 (omega(2)), 137 (omega(3)) and 145 (omega(4)) meV that originate from a range of different local structures associated with different configurations of the hydride ions and oxygen vacancies in the materials. Crucially, the combined analyses of INS and DFT data confirm the presence of both nearest and next-nearest neighbouring oxygen vacancies to the hydride ions. This supports previous findings from quasielastic neutron scattering experiments, that the hydride ion transport is governed by jump diffusion dynamics between neighbouring and next-nearest neighbouring hydride ion-oxygen vacancy local structures. Furthermore, the investigation of the momentum transfer dependence of the INS spectrum is used to derive the mean square displacement of the hydride ions, which is shown to be in excellent agreement with the calculations. Analysis of the mean square displacement confirms that the hydrogen vibrational motions are localized in nature and only very weakly affected by the dynamics of the surrounding perovskite structure. This insight motivates efforts to identify alternative host lattices that allow for a less localization of the hydride ions as a route to higher hydride ion conductivities.
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| 6. |
- Karlsson, Maths, 1978, et al.
(författare)
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Neutron Reflectivity in Corrosion Research on Metals
- 2024
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Ingår i: ACS Materials Au. - 2694-2461. ; 4:4, s. 346-353
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Forskningsöversikt (refereegranskat)abstract
- Neutron reflectivity (NR) is potentially a powerful tool for characterizing chemical and morphological changes in thin films and at buried interfaces in corrosion science. While the scope of NR is limited by its inherent demands for low surface roughness and high sample planarity, these drawbacks are compensated for by the unique ability to detect light elements and distinguish between isotopes. Furthermore, the generally weak absorption of neutrons by matter allows the use of bulky sample environments and in situ experiments. In particular, the layer thickness range of 3-100 nm accessible by NR is appropriate for studying air-formed films and passive films, which are crucial for the ability of metallic materials to resist corrosion, as well as for investigating the interaction of metal surfaces with hydrogen and its compounds, e.g., water. Also, NR is suitable for studying early stages of oxide growth on metals at high temperature, including the transition from Cabrera-Mott-type films to Wagner-type growth. Here, we outline key characteristics of NR as applied to the study of corrosion of metals, exemplified by earlier work, and discuss perspectives for future work in the field. The aim of our work is to stimulate the application of the unique capabilities of NR to corrosion science.
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| 7. |
- Mazzei, Laura, 1988
(författare)
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Local structure and dynamics of proton and hydride-ion conducting perovskite type oxides
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proton and hydride-ion conducting oxides show potential for application in several technological devices, such as solid oxide fuel cells and batteries. However, fundamental properties pertaining to the local structure and conduction mechanisms in these materials are unclear. Such fundamental knowledge is crucial for the development of novel materials and, ultimately, for their application in technological devices. This thesis reports on investigations of local structure and dynamics in two families of hydrogen containing perovskite structured oxides, namely proton-conducting BaZr xM 1- x O3H x ( M = In, Sc and Y, x ≤ 0.5) and hydride-ion conducting BaTiO3- x H x ( x ≤ 0.15). For the proton conducting BaZr x M1- x O3H x materials, the investigations focused on the nature of the proton sites in polycrystalline powder samples and were performed using inelastic neutron scattering and infrared and Raman spectroscopy combined with computer simulations. The results reveal the presence of a distribution of different types of proton sites, which were virtually the same for all chemical compositions except for a high level ( x ≥ 0.5) of In-doping. It is argued that the high In-doping results in the presence of additional proton sites located in distorted structural arrangements and which resemble those found in the hydrated form of the brownmillerite structured Ba2In2O5 system. It is also shown that the local environment for a specific proton changes over time due to the lattice vibrational dynamics. Additionally, thin-film samples were investigated by means of X-ray and neutron reflectivity and nuclear reaction analysis, with the aim to obtain details about the incorporation and distribution of protons in the samples. A key result is the observation of a thin (3-4 nm) proton-rich layer near to the surface of the films. This layer features proton sites characterized by relatively week hydrogen-bond interactions and a reduced proton mobility compared to the bulk of the film. The studies on hydride-ion conducting BaTiO3- x H x materials focused on revealing the nature of the local environments of the hydride ions and were performed using inelastic neutron scattering techniques and computer simulations. It is found that the presence of oxygen vacancies in the proximity of the hydride ions significantly influences their local environments and the vibrational properties.
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| 8. |
- Mazzei, Laura, 1988, et al.
(författare)
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Phonon spectra of pure and acceptor doped BaZrO3 investigated with visible and UV Raman spectroscopy
- 2020
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 32:40
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Tidskriftsartikel (refereegranskat)abstract
- We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO3 and a 500 nm thick film of its Y-doped, proton conducting, counterpart BaZr0.8Y0.2O2.9. Analysis of the Raman spectra measured using different excitation energies (between 3.44 eV and 5.17 eV) reveals the activation of strong resonance Raman effects involving all lattice vibrational modes. Specifically, two characteristic energies were identified for BaZrO3, one around 5 eV and one at higher energy, respectively, and one for BaZr0.8Y0.2O2.9, above 5 eV. Apart from the large difference in spectral intensity between the non-resonant and resonant conditions, the spectra are overall similar to each other, suggesting that the vibrational spectra of the perovskites are stable when investigated using an UV laser as excitation source. These results encourage further use of UV Raman spectroscopy as a novel approach for the study of lattice vibrational dynamics and local structure in proton conducting perovskites, and open up for, e.g., time-resolved experiments on thin films targeted at understanding the role of lattice vibrations in proton transport in these kinds of materials.
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| 9. |
- Mazzei, Laura, 1988
(författare)
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Protons in In-doped BaZrO3: incorporation, distribution and local environments
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acceptor doped proton conducting oxides are currently of large interest for their potential application as electrolyte materials in the future generation of solid oxide fuel cells. However, their proton conductivities are still lower than the target conductivity required for practical applications. The development of new materials with better performance depends on the advance of our understanding of the atomic-scale structure and dynamics, and their coupling with macroscopic proton conductivity, in the currently available materials. The aim of this thesis is to obtain new insights into the structure and dynamics in In-doped BaZrO3, one of the most investigated and promising classes of proton conducting oxides. To achieve this aim, the thesis is divided into two, complementary, research themes. The first research theme is dedicated to the analysis of the O-H vibrational spectra and a detailed characterization of the different proton sites present. Of specific interest is the nature of the hydrogen bond between the protons and neighboring oxygen atoms, O-H···O, which relates to the proton conducting properties. The second research theme focuses on studies of the proton concentration depth profile and proton conductivity in thin films of the same material. The investigations were performed using a combination of inelastic neutron scattering, infrared spectroscopy, molecular dynamics simulations, X-ray diffraction, Rutherford backscattering, X-ray and neutron reflectivity, nuclear reaction analysis and impedance spectroscopy. The results show that for low In-doping levels the protons are predominantly found close to the dopant atoms. These proton sites are characterized by a relatively weak hydrogen bonding and act as traps for the protons. For higher In-doping levels the results reveal the presence of a growing population of proton sites associated with stronger hydrogen bonds, and the trapping effect around the dopant atoms is now less pronounced, or even removed. In the studies of thin film samples, a key result is the observation of the presence of a thin proton-enriched near-surface region, characterized by relatively weak hydrogen bonding and lower proton mobility compared to the bulk of the material.
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| 10. |
- Mazzei, Laura, 1988, et al.
(författare)
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Structure and Conductivity of Epitaxial Thin Films of In-Doped BaZrO3-Based Proton Conductors
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:50, s. 28415-28422
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial thin films of the proton-conducting perovskite BaZr0.53In0.47O3-delta H0.47-2 delta, grown by pulsed laser deposition, were investigated in their hydrated and dehydrated conditions through a multitechniqu approach with the aim to study the structure and proton concentration depth profile and their relationship to proton conductivity. The techniques used were X-ray diffraction, X-ray and neutron reflectivity, nuclear reaction analysis, and Rutherford backscattering, together with impedance spectroscopy. The obtained proton conductivity and activation energy are comparable to literature values for the bulk conductivity of similar materials, thus showing that grain-boundary conductivity is negligible due to the high crystallinity of the film. The results reveal an uneven proton concentration depth profile, with the presence of a 3-4 nm thick, proton-rich layer with altered composition, likely characterized by cationic deficiency. While this surface layer either retains or reobtains protons after desorption and cooling to room temperature, the bulk of the film absorbs and desorbs protons in the expected mariner. It is suggested that the protons in the near-surface, proton rich region are located in proton sites characterized by relatively strong O-H bonds due to weak hydrogen-bond interactions to neighboring oxygen atoms and that the mobility of protons in these sites is generally lower than in proton sites associated with stronger hydrogen bonds. It follows that strongly hydrogen-bonding configurations are important for high proton mobility.
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