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Crystals
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Metal Oxides: Crystal Structure, Synthesis and Characterization
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Metal Oxides: Crystal Structure, Synthesis and Characterization

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

Deadline for manuscript submissions: closed (31 May 2024) | Viewed by 20870

Special Issue Editors

Dr. Karolina Siedliska

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Guest Editor
Department of Electronics and Information Technology, Lublin University of Technology, Lublin, Poland
Interests: mössbauer spectroscopy; ternary oxides; delafossites
Special Issues, Collections and Topics in MDPI journals
Dr. Kamila Komędera

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Guest Editor
Department of Physics, Pedagogical University of Krakow, Krakow, Poland
Interests: mössbauer spectroscopy; magnetic materials; superconductors
Special Issues, Collections and Topics in MDPI journals
Dr. Raffaello Mazzaro

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Guest Editor
CNR-IMM Bologna, Via Piero Gobetti 101, 40139 Bologna, Italy
Interests: metal oxides; semiconductor nanocrystals; energy conversion; luminescent materials; low-dimensional systems
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Metal oxides have been extensively explored in recent years due to their great variety of functional properties that make them ideal candidates for a wide range of applications in solar cells, energy storage devices, gas sensors, optoelectrical devices, catalysis, etc. Particular emphasis is paid to developing materials which exhibit more than one combined exciting features, which provides opportunities for observing new interesting phenomena (e.g., multiferroicity).

A metal oxide’s properties strongly depend on the oxide’s crystal structure, composition, defects, doping, etc., which determine its magnetic, optical, chemical, electrical, and mechanical characteristics. In addition, synthesis methods and growth parameters strongly determine a material’s morpho-structural characteristics and physicochemical properties.

This Special Issue is focused on methods for the synthesis and characterization of metal oxides in a wide range of forms, from crystals and nanoparticles to thin films and multilayer structures (superlattices, metamaterials, devices, etc.) with novel multifunctional characteristics that combine at least two properties: electrical and optical, electrical and magnetic, optical and magnetic, electrical and mechanical, thermal and chemical, etc.  As Guest Editor, I invite you to submit contributions to this Special Issue. Interdisciplinary approaches toward the preparation of new forms of metal oxides and the exploration of their properties are encouraged.

Dr. Karolina Siedliska
Dr. Kamila Komędera
Dr. Raffaello Mazzaro
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 2100 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

  • metal oxides
  • material characterization
  • synthesis
  • crystal structure
  • nanomaterials
  • applications

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Published Papers (11 papers)

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Editorial

Jump to: Research, Review

3 pages, 172 KiB  
Editorial
Metal Oxides: Crystal Structure, Synthesis and Characterization
by Karolina Siedliska
Crystals 2024, 14(11), 991; https://doi.org/10.3390/cryst14110991 - 17 Nov 2024
Viewed by 315
Abstract
Solid metal oxides are widely recognized for their ubiquitous presence and multifaceted utility in everyday applications [...] Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)

Research

Jump to: Editorial, Review

19 pages, 3750 KiB  
Article
Visible-Light Spectroscopy and Rock Magnetic Analyses of Iron Oxides in Mixed-Mineral Assemblages
by Christopher J. Lepre, Owen M. Yazzie and Benjamin R. Klaus
Crystals 2024, 14(7), 644; https://doi.org/10.3390/cryst14070644 - 13 Jul 2024
Cited by 1 | Viewed by 890
Abstract
Iron oxide assemblages are central to many pursuits, ranging from Mars exploration to environmental remediation. Oxides and oxyhydroxides of iron both carry the special properties of color and magnetism. In this paper, we use visible-light spectroscopy and rock magnetic data collected at varying [...] Read more.
Iron oxide assemblages are central to many pursuits, ranging from Mars exploration to environmental remediation. Oxides and oxyhydroxides of iron both carry the special properties of color and magnetism. In this paper, we use visible-light spectroscopy and rock magnetic data collected at varying temperatures (~77–973 K) to analyze the concentrations and identities of iron oxides found in natural hematite-dominated samples that were obtained from a scientific drill core of Late Triassic red beds in the American Southwest. Our results suggest that hematite colorization of Earth materials varies from red to blue/purple as crystal size increases. Second-derivative analysis of the collected visible-light spectra allows this variation to be measured through the characteristic wavelength band position. Magnetic coercivity data indicate “hardness” differences that also may suggest smaller grain sizes are associated with redder colors. Yellowish maghemite and goethite have overlapping characteristic wavelength band positions that make it challenging to distinguish their contributions to mixed assemblages from visible-light data alone. Remanent magnetizations acquired at ~77 K and room temperature suggest the presence of hematite and a low-coercivity phase that may be maghemite and/or oxidized magnetite. However, we interpret this phase as maghemite in order to explain the changes in iron oxide concentrations indicated by visible-light intensities near ~425 nm and because the thermal demagnetization data suggest that goethite is absent from the samples. Future research that increases the resolution of hematite, maghemite, and goethite detection in experimental and natural samples will provide opportunities to refine the study of past climates and constrain soil iron availability under future changes in global moisture and temperature. Multimethod datasets improve understanding of environmental conditions that cause iron oxides assemblages to shift in phase dominance, grain size, and crystallinity. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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15 pages, 4908 KiB  
Article
Optical and Optoelectrical Properties of Ternary Chalcogenide CuInS2/TiO2 Nanocomposite Prepared by Mechanochemical Synthesis
by Erika Dutkova, Matej Baláž, Jaroslav Kováč, Nina Daneu, Adelia Kashimbetova, Jaroslav Briančin, Jaroslav Kováč, Jr., Soňa Kováčová and Ladislav Čelko
Crystals 2024, 14(4), 324; https://doi.org/10.3390/cryst14040324 - 30 Mar 2024
Viewed by 1122
Abstract
In this work, a nanocomposite consisting of ternary chalcogenide CuInS2 and TiO2 was prepared and its optical and optoelectrical properties were investigated. The CuInS2/TiO2 nanocomposite was produced via one-step mechanochemical synthesis and characterized from the crystal structure, microstructural, [...] Read more.
In this work, a nanocomposite consisting of ternary chalcogenide CuInS2 and TiO2 was prepared and its optical and optoelectrical properties were investigated. The CuInS2/TiO2 nanocomposite was produced via one-step mechanochemical synthesis and characterized from the crystal structure, microstructural, morphology, surface, optical, and optoelectrical properties viewpoints. X-ray diffraction confirmed the presence of both components, CuInS2 and TiO2, in the nanocomposite and revealed a partial transformation of anatase to rutile. The presence of both components in the samples was also proven by Raman spectroscopy. HRTEM confirmed the nanocrystalline character of the samples as crystallites ranging from around 10 nm and up to a few tens of nanometers were found. The presence of the agglomerated nanoparticles into larger grains was proven by SEM. The measured optical properties of CuInS2, TiO2, and CuInS2/TiO2 nanocomposites demonstrate optical bandgaps of ~1.62 eV for CuInS2 and 3.26 eV for TiO2. The measurement of the optoelectrical properties showed that the presence of TiO2 in the CuInS2/TiO2 nanocomposite increased its conductivity and modified the photosensitivity depending on the ratio of the components. This study has demonstrated the possibility of preparing a CuInS2/TiO2 nanocomposite material with promising applications in optoelectronics in the visible region in an eco-friendly manner. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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16 pages, 7643 KiB  
Article
Combustion Synthesis of Zirconium-Doped Ceria Nanocatalyst
by Katarina Mužina, Stanislav Kurajica, Helena Bach-Rojecky, Filip Brleković and Marina Duplančić
Crystals 2024, 14(2), 108; https://doi.org/10.3390/cryst14020108 - 23 Jan 2024
Viewed by 1644
Abstract
Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce1−xZrxO2, [...] Read more.
Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce1−xZrxO2, where x = 0, 0.1, 0.2, and 0.3) were prepared by combustion synthesis using glycine as the fuel and cerium and zirconium nitrate as oxidants. The obtained powders were characterized using X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, differential thermal and thermogravimetric analysis, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The combustion temperature increases with the increase in zirconium content in the samples, but the XRD patterns exclusively show ceria diffraction peaks. The crystallite sizes are in the range from 25.2 to 11.7 nm, and do not vary substantially after thermal treatment, indicating the good thermal stability of the prepared nanocatalysts. XPS analysis showed that the surface amount of zirconium is lower than the nominal and that the ceria sample with 10 mol. % of zirconium has a higher amount of oxygen vacancies than the 30 mol. % Zr-doped sample. The 10 mol. % Zr-doped sample displays the best catalytic activity in the BTEX (benzene, toluene, ethylbenzene, and o-xylene) oxidation process. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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12 pages, 6637 KiB  
Article
Observation of Metal–Insulator Transition (MIT) in Vanadium Oxides V2O3 and VO2 in XRD, DSC and DC Experiments
by Paweł Polak, Jan Jamroz and Tomasz K. Pietrzak
Crystals 2023, 13(9), 1299; https://doi.org/10.3390/cryst13091299 - 23 Aug 2023
Cited by 2 | Viewed by 1691
Abstract
Due to metal–insulator transitions occurring in those compounds, materials and devices based on vanadium (III) and (IV) oxides draw increasing scientific attention. In this paper, we observed the transitions in both oxides using contemporary laboratory equipment. Changes in the crystallographic structure were precisely [...] Read more.
Due to metal–insulator transitions occurring in those compounds, materials and devices based on vanadium (III) and (IV) oxides draw increasing scientific attention. In this paper, we observed the transitions in both oxides using contemporary laboratory equipment. Changes in the crystallographic structure were precisely investigated as a function of the temperature with a step of 2 °C. Thermal effects during transitions were observed using differential scanning calorimetry. The DC conductivity of the materials was measured quasi-continuously as a function of the temperature. All the experiments were consistent and showed considerable hysteresis of the metal–insulator transition in both vanadium oxides. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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21 pages, 3543 KiB  
Article
Photocatalytic and Antimicrobial Activity of Titanium(IV)-Oxo Clusters of Different Core Structure
by Barbara Kubiak, Piotr Piszczek, Aleksandra Radtke, Tadeusz Muzioł, Grzegorz Wrzeszcz and Patrycja Golińska
Crystals 2023, 13(7), 998; https://doi.org/10.3390/cryst13070998 - 22 Jun 2023
Cited by 3 | Viewed by 1485
Abstract
The purpose of this paper is to assess the relationship between the core architecture of titanium(IV)-oxo complexes (TOCs) known as {TiaOb} and their photocatalytic and antimicrobial activity. The following TOCs: [Ti6O4(OiBu)8(O [...] Read more.
The purpose of this paper is to assess the relationship between the core architecture of titanium(IV)-oxo complexes (TOCs) known as {TiaOb} and their photocatalytic and antimicrobial activity. The following TOCs: [Ti6O4(OiBu)8(O2C13H9)8] · 2(CH3)2CO (1), [Ti6O6(OiBu)6(O2C13H9)6] (2), [Ti6O6(OiBu)6(O2C13H9)6] (3), [Ti3O(OiPr)8(O2C13H9)2] (4), and [Ti4O2(OiBu)10(O2C13H9)2] (5), where -O2C13H9represents 9-fluorene-carboxylate ligands, werestudied to investigate thiseffect. The structures of (1)–(5) were confirmed using single-crystal X-ray diffraction and spectroscopic methods. Since TOCs can be sensitive to hydrolysis processes, their photocatalytic and antimicrobial activity was evaluated after dispersing them in a polymer matrix, which acted as a protective agent against the aquatic environment. The results revealed that the photocatalytic activity of the studied TOCs follows the trend (2) > (5) > (4) > (1) in both the UV and visible ranges. All studied oxo complexes exhibited strong antibacterial activity against Gram-positive strains and weaker activity against Gram-negative strains. The proposed mechanism of the antimicrobial activity of TOCs assumes that this effect is associated with the generation of reactive oxygen species (ROS) on the surface of composite samples. Samples of PMMA + (1) 10 wt.% and PMMA + (5) 20 wt.%, in which both O− and O2− paramagnetic species were observed in the electron paramagnetic spectroscopy (EPR) spectra, demonstrated the highest antimicrobial activity. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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11 pages, 7747 KiB  
Article
Structural Disorder of CuO, ZnO, and CuO/ZnO Nanowires and Their Effect on Thermal Conductivity
by Helver Augusto Giraldo-Daza, José Darío Agudelo-Giraldo, César Leandro Londoño-Calderón and Henry Reyes-Pineda
Crystals 2023, 13(6), 953; https://doi.org/10.3390/cryst13060953 - 15 Jun 2023
Viewed by 1421
Abstract
In this work, the structural defects and the thermal conductivity of CuO, ZnO, and CuO/ZnO nanowires have been studied, using molecular dynamics simulation with COMB3 potential. The initial parameters and atoms positions were taken from reports of bulk materials with tenorite and wurtzite [...] Read more.
In this work, the structural defects and the thermal conductivity of CuO, ZnO, and CuO/ZnO nanowires have been studied, using molecular dynamics simulation with COMB3 potential. The initial parameters and atoms positions were taken from reports of bulk materials with tenorite and wurtzite structures, respectively. Nanowires were grown along the c-axis, as observed experimentally. The results confirm the defects apparition in the systems after simulation with a formation of grains to reduce the energy of the nanowires. In the CuO nanowires case, the lack of periodicity in the basal plane causes a contraction effect over the network parameter b of the monoclinic structure with a Cu-O distance reduction. [A constriction effect on inclined planes, as a product of surface charges, deforms the nanowire, generating undulations. In ZnO nanowires, a decrease in the Zn-Zn distance produced a contraction in the nanowire length. A constriction effect was evident on the surface charges. It presented a bond reduction effect, which was larger at the ends of the nanowire. In CuO/ZnO nanowires, the structural defects come from the distortions of the crystalline lattice of the ZnO rather than CuO. The thermal conductivity of the nanowires was calculated at temperatures between 200 K and 600 K using the Green–Kubo equation. Results showed similar values to those reported experimentally, and the characteristic maximum with similar trends to those observed in semiconductors. Our results suggest that structural defects appear in nanowires grown on the free substrate, and are not related to the lattice mismatch. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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14 pages, 825 KiB  
Article
Thermal Expansion and Phase Transformation up to 1200 °C of Metastable Aluminas Produced by Flame Spraying
by Tilo Zienert and Christos Georgios Aneziris
Crystals 2023, 13(5), 743; https://doi.org/10.3390/cryst13050743 - 29 Apr 2023
Cited by 4 | Viewed by 1888
Abstract
The transition aluminas δ1 and the cubic, non-spinel-type η-Al2O3 were detected in addition to α-Al2O3 in flame-sprayed material. Their transitions from room temperature up to 1200 °C were investigated by high-temperature XRD measurements. Structural [...] Read more.
The transition aluminas δ1 and the cubic, non-spinel-type η-Al2O3 were detected in addition to α-Al2O3 in flame-sprayed material. Their transitions from room temperature up to 1200 °C were investigated by high-temperature XRD measurements. Structural changes with time and temperature were observed for all transition aluminas (η-, δ1- and θ-Al2O3). The phases followed the expected transition sequence of η→δ1→θ→α and showed mainly linear, temperature-independent transition rates. Based on the determined thermal expansion of the phases, it is proposed that the metastable transitions are at least partly mechanically induced. In addition, a second-order phase transition from η→θ might be indicated around 1050–1075 °C by the determined trends of density. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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10 pages, 2734 KiB  
Article
Oxygen Vacancies in Zirconia and Their Migration: The Role of Hubbard-U Parameters in Density Functional Theory
by Ralph Gebauer
Crystals 2023, 13(4), 574; https://doi.org/10.3390/cryst13040574 - 28 Mar 2023
Viewed by 2447
Abstract
Cubic zirconia (c-ZrO2) is studied using Density Functional Theory with Hubbard-U corrections (DFT+U). It is shown that the determination of the U-parameters from first principles leads to values for U(Zr-4d) and U(O-2p) which are very different from standard [...] Read more.
Cubic zirconia (c-ZrO2) is studied using Density Functional Theory with Hubbard-U corrections (DFT+U). It is shown that the determination of the U-parameters from first principles leads to values for U(Zr-4d) and U(O-2p) which are very different from standard choices. The calculated band gap with these values for U closely matches the experimental gap. Oxygen vacancies are studied using this approach, and it is found that it is possible to closely reproduce the vacancy migration energies calculated with a hybrid functional. The oxygen vacancy is associated with two excess electrons which localize in the vacancy’s cavity. In the presence of these excess electrons, the barrier for vacancy migration is very high. If instead, a charged vacancy VO2+ is considered, its mobility increases considerably—an effect that is attributed to the absence of space charges localized in the cavity. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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15 pages, 18485 KiB  
Article
Characterization of Ti/SBA-15 Composites Synthesized by Chemical Vapour Deposition of Organic Titanium Compounds
by Leszek Ruchomski, Jan Ozimek, Karolina Siedliska, Konstantinos N. Raftopoulos and Krzysztof Pielichowski
Crystals 2023, 13(2), 288; https://doi.org/10.3390/cryst13020288 - 8 Feb 2023
Cited by 2 | Viewed by 2007
Abstract
The chemical vapour deposition technique was applied to obtain Ti/SBA-15 composites. Titanium(IV) tetraisopropoxide (TTIP) and titanium(IV) tetrabutoxide (TNBT) as sources of TiO2 were deposited on mesoporous silica (SBA-15) from the gaseous phase at 180–200 °C and treated at 250 °C in air. [...] Read more.
The chemical vapour deposition technique was applied to obtain Ti/SBA-15 composites. Titanium(IV) tetraisopropoxide (TTIP) and titanium(IV) tetrabutoxide (TNBT) as sources of TiO2 were deposited on mesoporous silica (SBA-15) from the gaseous phase at 180–200 °C and treated at 250 °C in air. X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy were used for structural investigations. Moreover, energy-dispersive X-ray spectroscopy studies and electrophoretic mobility measurements were conducted. Investigations revealed that Ti ions were mainly deposited on the SBA-15 surface as a thin layer of amorphous TiO2. However, Ti ions were not detected in the composites synthesized using TNBT as the starting reagent. The thickness of the deposited titanium oxide layer was estimated as 6–7 nm, and the porous silica structure has not been damaged. Moreover, the Ti ions deposition on the SBA-15 surface did not significantly change the investigated Ti/SBA-15 composites’ thermal stability compared to pristine silica. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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Review

Jump to: Editorial, Research

21 pages, 777 KiB  
Review
ZnO and ZnO-Based Materials as Active Layer in Resistive Random-Access Memory (RRAM)
by Ewelina Nowak, Edyta Chłopocka and Mirosław Szybowicz
Crystals 2023, 13(3), 416; https://doi.org/10.3390/cryst13030416 - 28 Feb 2023
Cited by 18 | Viewed by 4920
Abstract
In this paper, an overview of the influence of various modifications on ZnO-based RRAM has been conducted. Firstly, the motivation for creating new memory technology is presented. The resistive switching mechanism is explained, including its response to the selection of active layers and [...] Read more.
In this paper, an overview of the influence of various modifications on ZnO-based RRAM has been conducted. Firstly, the motivation for creating new memory technology is presented. The resistive switching mechanism is explained, including its response to the selection of active layers and electrodes. A comparison of ZnO devices assembled via different deposition methods is made. Additional treatment of the active layer and electrodes improving the performance are reported. This work gives an overview of the influence of different dopants on the characteristics of the device. The manuscript overviews the previous investigation of inclusion of inserting layers and nanostructures into ZnO-based RRAM. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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