Special Issue "Electronic Phenomena of Transition Metal Oxides"

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

Deadline for manuscript submissions: 31 December 2019.

Special Issue Editors

Dr. Christian Rodenbücher
E-Mail Website
Guest Editor
Institute of Energy and Climate Research (IEK-3), Forschungszentrum Jülich, 52425 Jülich, Germany
Interests: surface physics; scanning probe microscopy; electrochemistry; metal oxides
Prof. Krzysztof Szot
E-Mail Website
Guest Editor
August Chelkowski Institute of Physics, University of Silesia, 40-007 Katowice, Poland
Interests: perovskites; dislocations; phase transitions; resistive switching

Special Issue Information

Dear Colleagues,

Transition metal oxides have become the subject of numerous research studies due to their unique electronic properties. In particular, in recent years they have attracted attention as high-k dielectrics, as memristive materials for energy-efficient computing, and as catalysts for water splitting allowing the storage of renewable energy. Many electronic phenomena present in these transition metal oxides are related to the fact that the transition metal ion can adopt different valence states. By exposing the metal oxide to an appropriate gradient of electrochemical potential, the valence state can be changed allowing for the tailoring the electronic properties of the system. Moreover, such a valence change can even occur locally, confined to the nanoscale dimensions, which enables the formation of conducting paths inside a non-conducting matrix. As a typical example, the preferential reduction of dislocations in the model material SrTiO3 can be mentioned, which can be exploited for high-density memristive devices.

The Special Issue on the “Electronic Phenomena of Transition Metal Oxides” aims to provide a platform for the presentation of novel insights in the electronic structure of transition metal oxides, both from the theoretical and experimental point of view.

We would like to invite researchers working within the general framework of the Special Issue to contribute to the scientific discussion.

Dr. Christian Rodenbücher
Prof. Dr. Krzysztof Szot
Guest Editors

Manuscript Submission Information

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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.

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Keywords

  • Metal–insulator transitions and superconductivity
  • Atomistic processes at surfaces, interfaces, and extended defects
  • Electronic structure and lattice dynamics
  • Redox reactions and oxygen transport
  • Segregation and phase transformations

Published Papers (3 papers)

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Research

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Open AccessArticle
Electronic Structure of Oxygen-Deficient SrTiO3 and Sr2TiO4
Crystals 2019, 9(11), 580; https://doi.org/10.3390/cryst9110580 - 07 Nov 2019
Abstract
The conductive behavior of the perovskite SrTiO 3 is strongly influenced by the presence of oxygen vacancies in this material, therefore the identification of such defects with spectroscopic methods is of high importance. We use density functional theory to characterize the defect-induced states [...] Read more.
The conductive behavior of the perovskite SrTiO 3 is strongly influenced by the presence of oxygen vacancies in this material, therefore the identification of such defects with spectroscopic methods is of high importance. We use density functional theory to characterize the defect-induced states in SrTiO 3 and Sr 2 TiO 4 . Their signatures at the surface, the visibility for scanning tunneling spectroscopy and locally conductive atomic force microscopy, and the core-level shifts observed on Ti atoms in the vicinity of the defect are studied. In particular, we find that the exact location of the defect state (e.g., in SrO or TiO 2 planes relative to the surface) are decisive for their visibility for scanning-probe methods. Moreover, the usual distinction between Ti 3 + and Ti 2 + species, which can occur near defects or their aggregates, cannot be directly translated in characteristic shifts of the core levels. The width of the defect-induced in-gap states is found to depend critically on the arrangement of the defects. This also has consequences for the spectroscopic signatures observed in so-called resistive switching phenomena. Full article
(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides)
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Open AccessArticle
Intrinsic Ferroelectricity in Charge-Ordered Magnetite
Crystals 2019, 9(11), 546; https://doi.org/10.3390/cryst9110546 - 23 Oct 2019
Abstract
Single crystalline magnetite Fe3O4 was investigated at low temperatures in the charge ordered state by electric measurements and time-resolved diffraction with voltage applied in-situ. Dielectric spectroscopy indicates relaxor ferroelectric characteristics, with polarization switching observably only at sufficiently low temperatures and [...] Read more.
Single crystalline magnetite Fe3O4 was investigated at low temperatures in the charge ordered state by electric measurements and time-resolved diffraction with voltage applied in-situ. Dielectric spectroscopy indicates relaxor ferroelectric characteristics, with polarization switching observably only at sufficiently low temperatures and in a suitably chosen time-window. PUND measurements with a ms time scale indicate a switchable polarization of about 0.6 µC/cm2. Significant switching occurs only above a threshold field of about 3 kV/mm, and it occurs with a time delay of about 20 µs. The time-resolved diffraction experiment yields, for sufficiently high voltage pulses, a systematic variation by about 0.1% of the intensity of the ( 2 , 2 ¯ , 10 ¯ ) Bragg reflection, which is attributed to structural switching of domains of the non-centrosymmetric C c structure to its inversion twins, providing proof of intrinsic ferroelectricity in charge ordered magnetite. Full article
(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides)
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Open AccessReview
Polaronic Emergent Phases in Manganite-based Heterostructures
Crystals 2019, 9(10), 489; https://doi.org/10.3390/cryst9100489 - 22 Sep 2019
Abstract
Transition metal functional oxides, e.g., perovskite manganites, with strong electron, spin and lattice correlations, are well-known for different phase transitions and field-induced colossal effects at the phase transition. Recently, the interfaces between dissimilar perovskites were shown to be a promising concept for the [...] Read more.
Transition metal functional oxides, e.g., perovskite manganites, with strong electron, spin and lattice correlations, are well-known for different phase transitions and field-induced colossal effects at the phase transition. Recently, the interfaces between dissimilar perovskites were shown to be a promising concept for the search of emerging phases with novel functionalities. We demonstrate that the properties of manganite films are effectively controlled by low dimensional emerging phases at intrinsic and extrinsic interfaces and appeared as a result of symmetry breaking. The examples include correlated Jahn–Teller polarons in the phase-separated (La1−yPry)0.7Ca0.3MnO3, electron-rich Jahn–Teller-distorted surface or “dead” layer in La0.7Sr0.3MnO3, electric-field-induced healing of “dead” layer as an origin of resistance switching effect, and high-TC ferromagnetic emerging phase at the SrMnO3/LaMnO3 interface in superlattices. These 2D polaronic phases with short-range electron, spin, and lattice reconstructions could be extremely sensitive to external fields, thus, providing a rational explanation of colossal effects in perovskite manganites. Full article
(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides)
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