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Crystals
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Diffusion and Degradation Phenomena in Solid Oxide Materials
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Diffusion and Degradation Phenomena in Solid Oxide Materials

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Metals and Alloys".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 14596

Special Issue Editors

Dr. Christian Rodenbücher

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Guest Editor
Forschungszentrum Jülich, Institute of Energy and Climate Research/Electrochemical Process Engineering (IEK-14), Jülich, Germany
Interests: solid oxides; perovskites; electrochemistry; renewable energy; surface physics
Special Issues, Collections and Topics in MDPI journals
Dr. Carsten Korte

E-Mail Website
Guest Editor
Forschungszentrum Jülich, Institute of Energy and Climate Research/Electrochemical Process Engineering (IEK-14), Germany
Interests: physical chemistry of solids; ionic transport across/along interfaces; electrochemistry; renewable energy
Dr. Qingping Fang

E-Mail Website
Guest Editor
Institute of Energy and Climate Research/Electrochemical Process Engineering (IEK-14), Forschungszentrum Jülich, Jülich, Germany
Interests: solid oxide cells and stack; electrochemistry; renewable energy

Special Issue Information

Dear Colleagues,

Solid oxide fuel cells (SOFCs) and solid oxide electrolyzer cells (SOECs) are key elements for a future emission-free energy system as they allow for storing energy from intermittent renewable sources via electrochemical energy conversion. In order to induce a sufficient ionic conductivity in the solid electrolyte, high operation temperatures of 500 °C to 900 °C are necessary, which demand a sufficient long-term stability, especially under varying applied loads.

To optimize the material performance, a deeper understanding of the fundamental diffusion processes in mixed ionic–electronic conductors under gradients of the chemical and electrical potential is needed. Therefore, the relation between crystallographic structure and ionic conductivity is one of the pivotal research questions. As interfaces and inner surfaces such as grain boundaries and dislocations can also play an important role in the electrochemical performance of an oxide but may simultaneously act as a seed for irreversible phase transformations, the analysis and comparison of the properties of single crystals and ceramics can assist in building heuristic models for mass transport in solid oxides.

The Special Issue aims at serving as a platform for not only research related to the characterization of conventional solid oxides used as fuel cell electrolytes and electrodes, but also research on the synthesis and characterization of novel oxides with enhanced ionic conductivity.

Dr. Christian Rodenbücher
Dr. Carsten Korte
Dr. Qingping Fang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Solid oxides
  • Mixed ionic–electronic conductors
  • Oxygen diffusion
  • Electrode/electrolyte interfaces
  • Grain boundaries and dislocations
  • Phase transformations

Published Papers (5 papers)

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Research

17 pages, 1302 KiB  
Article
Effects of Electron Correlation inside Disordered Crystals
by Sergei P. Kruchinin, Roberts I. Eglitis, Vitaliy P. Babak, Iryna G. Vyshyvana and Stanislav P. Repetsky
Crystals 2022, 12(2), 237; https://doi.org/10.3390/cryst12020237 - 9 Feb 2022
Cited by 3 | Viewed by 2387
Abstract
We propose a novel approach for characterising the electron spectrum of disordered crystals constructed from a Hamiltonian of electrons as well as phonons and a diagram approach for Green’s function. The system’s electronic states were modelled by means of the multi-band, tight-binding approach. [...] Read more.
We propose a novel approach for characterising the electron spectrum of disordered crystals constructed from a Hamiltonian of electrons as well as phonons and a diagram approach for Green’s function. The system’s electronic states were modelled by means of the multi-band, tight-binding approach. The system’s Hamiltonian is described based on the electron wave functions at the field of the atom nucleus. Our novel approach incorporates the long-range Coulomb interplay of electrons located in different lattice positions. Explicit interpretations of Green’s functions are derived using a diagram method. Equations are obtained for the vertex components for the mass operators of the electron–electron as well aselectron–phonon interplays. A system of equations for the spectrum of elementary excitations in the crystal is obtained, in which the vertex components for the mass operators of electron–electron as well as electron–phonon interplays are renormalised. Thismakes it possible to perform numerical computationsfor the system’s energy spectrum with a predetermined accuracy. In contrast to other approaches in which electron correlations are only taken into account in the limiting cases of an infinitely large and infinitesimal electron density, in this method, electron correlations are described in the general case of an arbitrary density. We obtained the cluster expansion of the density of states (DOS) of the disordered systems. We demonstrate that the addition of the electron-scattering mechanismsto the clusters is decreasing. This happens due to a growing number of positions in the cluster, which hang ontothe small parameter. The computing exactness is fixed by a small parameter for cluster expansion of Green’s functions of electrons as well as phonons. Full article
(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)
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9 pages, 1838 KiB  
Article
Is Reduced Strontium Titanate a Semiconductor or a Metal?
by Christian Rodenbücher, Christo Guguschev, Carsten Korte, Sebastian Bette and Kristof Szot
Crystals 2021, 11(7), 744; https://doi.org/10.3390/cryst11070744 - 25 Jun 2021
Cited by 3 | Viewed by 2242
Abstract
In recent decades, the behavior of SrTiO3 upon annealing in reducing conditions has been under intense academic scrutiny. Classically, its conductivity can be described using point defect chemistry and predicting n-type or p-type semiconducting behavior depending on oxygen activity. In contrast, many [...] Read more.
In recent decades, the behavior of SrTiO3 upon annealing in reducing conditions has been under intense academic scrutiny. Classically, its conductivity can be described using point defect chemistry and predicting n-type or p-type semiconducting behavior depending on oxygen activity. In contrast, many examples of metallic behavior induced by thermal reduction have recently appeared in the literature, challenging this established understanding. In this study, we aim to resolve this contradiction by demonstrating that an initially insulating, as-received SrTiO3 single crystal can indeed be reduced to a metallic state, and is even stable against room temperature reoxidation. However, once the sample has been oxidized at a high temperature, subsequent reduction can no longer be used to induce metallic behavior, but semiconducting behavior in agreement with the predictions of point defect chemistry is observed. Our results indicate that the dislocation-rich surface layer plays a decisive role and that its local chemical composition can be changed depending on annealing conditions. This reveals that the prediction of the macroscopic electronic properties of SrTiO3 is a highly complex task, and not only the current temperature and oxygen activity but also the redox history play an important role. Full article
(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)
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16 pages, 8809 KiB  
Article
Interactions of Ruddlesden-Popper Phases and Migration-Induced Field-Stabilized Polar Phase in Strontium Titanate
by Christian Ludt, Elena Ovchinnikova, Anton Kulikov, Dmitri Novikov, Sibylle Gemming, Dirk C. Meyer and Matthias Zschornak
Crystals 2021, 11(6), 693; https://doi.org/10.3390/cryst11060693 - 17 Jun 2021
Cited by 2 | Viewed by 2334
Abstract
This work focuses on the validation of a possible connection of the known Ruddlesden-Popper (RP) phases and the novel concept of the migration-induced field-stabilized polar (MFP) phase. To study this subject, model structures of RP phases in bulk strontium titanate are analyzed by [...] Read more.
This work focuses on the validation of a possible connection of the known Ruddlesden-Popper (RP) phases and the novel concept of the migration-induced field-stabilized polar (MFP) phase. To study this subject, model structures of RP phases in bulk strontium titanate are analyzed by means of density functional theory (DFT). The obtained geometries are compared to experimental MFP data. Good agreement can be found concerning atomic displacements in the pm range and lattice strain inferred by the RP phases. Looking at the energy point of view, the defect structures are on the convex hull of the Gibb’s free energy. Although the dynamics to form the discussed defect models are not addressed in detail, the interplay and stability of the described defect model will add to the possible structure scenarios within the near-surface region of strontium titanate. As a result, it can be suggested that RP phases generally favor the MFP formation. Full article
(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)
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13 pages, 1813 KiB  
Article
Comparative Hybrid Hartree-Fock-DFT Calculations of WO2-Terminated Cubic WO3 as Well as SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) Surfaces
by R. I. Eglitis, Juris Purans and Ran Jia
Crystals 2021, 11(4), 455; https://doi.org/10.3390/cryst11040455 - 20 Apr 2021
Cited by 46 | Viewed by 4336
Abstract
We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO2-terminated cubic WO3 (001) surface and analyzed the systematic trends in the WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO [...] Read more.
We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO2-terminated cubic WO3 (001) surface and analyzed the systematic trends in the WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface ab initio calculations. According to our first principles calculations, all WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, while all second-layer atoms relax upwards. The only two exceptions are outward relaxations of first layer WO2 and TiO2-terminated WO3 and PbTiO3 (001) surface O atoms. The WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface-band gaps at the Γ–Γ point are smaller than their respective bulk-band gaps. The Ti–O chemical bond populations in the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 bulk are smaller than those near the TiO2-terminated (001) surfaces. Conversely, the W–O chemical bond population in the WO3 bulk is larger than near the WO2-terminated WO3 (001) surface. Full article
(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)
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21 pages, 4677 KiB  
Article
Correlation between Structural and Transport Properties of Ca-Doped La Nickelates and Their Electrochemical Performance
by Elena Pikalova, Vladislav Sadykov, Ekaterina Sadovskaya, Nikita Yeremeev, Alexander Kolchugin, Alexander Shmakov, Zakhar Vinokurov, Denis Mishchenko, Elena Filonova and Vladimir Belyaev
Crystals 2021, 11(3), 297; https://doi.org/10.3390/cryst11030297 - 17 Mar 2021
Cited by 12 | Viewed by 2602
Abstract
This work presents the results from a study of the structure and transport properties of Ca-doped La2NiO4+δ. La2−xCaxNiO4+δ (x = 0–0.4) materials that were synthesized via combustion of organic-nitrate precursors and characterized by [...] Read more.
This work presents the results from a study of the structure and transport properties of Ca-doped La2NiO4+δ. La2−xCaxNiO4+δ (x = 0–0.4) materials that were synthesized via combustion of organic-nitrate precursors and characterized by X-ray diffraction (XRD), in situ XRD using synchrotron radiation, thermogravimetric analysis (TGA) and isotope exchange of oxygen with C18O2. The structure was defined as orthorhombic (Fmmm) for x = 0 and tetragonal (I4/mmm) for x = 0.1–0.4. Changes that occurred in the unit cell parameters and volume as the temperature changed during heating were shown to be caused by the excess oxygen loss. Typical for Ruddlesden–Popper phases, oxygen mobility and surface reactivity decreased as the Ca content was increased due to a reduction in the over-stoichiometric oxygen content with the exception of x = 0.1. This composition demonstrated its superior oxygen transport properties compared to La2NiO4+δ due to the enhanced oxygen mobility caused by structural features. Electrochemical data obtained showed relatively low polarization resistance for the electrodes with a low Ca content, which correlates well with oxygen transport properties. Full article
(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)
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