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Crystals
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Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition)
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Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition)

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

Deadline for manuscript submissions: 31 August 2025 | Viewed by 5127

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

E-Mail Website
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

E-Mail Website
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,

Following the successful first edition of this Special Issue of Crystals, we are pleased to announce that submissions to its second edition, entitled "Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition)", are now being accepted.

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 (7 papers)

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Research

Jump to: Review

13 pages, 6090 KiB  
Article
Carbochlorination Reduction Process of Waelz ZnO: Characterization of Resulting ZnO-Based Oxides
by Lorena Alcaraz, Belén Sotillo, Paloma Fernández and Félix A. López
Crystals 2025, 15(4), 326; https://doi.org/10.3390/cryst15040326 - 28 Mar 2025
Viewed by 185
Abstract
Zinc-based oxides are the main products obtained after the Waelz process, a metallurgical method used industrially for the treatment of electric arc furnaces. These oxides have certain impurities in their composition, which can be a disadvantage. Carbochlorination reduction reactions have proven to be [...] Read more.
Zinc-based oxides are the main products obtained after the Waelz process, a metallurgical method used industrially for the treatment of electric arc furnaces. These oxides have certain impurities in their composition, which can be a disadvantage. Carbochlorination reduction reactions have proven to be useful in eliminating certain impurities (especially Pb) through thermal treatments. In this work, a method for purifying Waelz oxide through carbochlorination reduction reactions is presented. Several experiments have been conducted with the aim of obtaining samples with potential end applications. A deep characterization of the purified oxides has been performed by means of X-ray microanalysis, X-ray diffraction, Raman spectroscopy, and cathodoluminescence. These measurements indicate the presence of ZnO and ZnFe2O4 in different proportions, depending on the different amounts of reducing and chlorinating agents used. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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13 pages, 3390 KiB  
Article
Mössbauer and Optical Investigations on Sr Doped M-Type BaFe12O19 Hexaferrites Produced via Autocombustion
by Benilde F. O. Costa, Adel Benali, Bruno J. C. Vieira, João C. Waerenborgh, João Pina, Yousra Marouani and Essebti Dhahri
Crystals 2025, 15(4), 291; https://doi.org/10.3390/cryst15040291 - 24 Mar 2025
Viewed by 269
Abstract
Ba1−xSrxFe12O19 (x = 0.0, 0.5 and 1.0) hard-magnetic nanohexaferrites prepared by autocombustion were primarily investigated using Mössbauer spectroscopy and optical studies. Morphological examination by electron scanning microscopy revealed that the particles agglomerated into grains with a [...] Read more.
Ba1−xSrxFe12O19 (x = 0.0, 0.5 and 1.0) hard-magnetic nanohexaferrites prepared by autocombustion were primarily investigated using Mössbauer spectroscopy and optical studies. Morphological examination by electron scanning microscopy revealed that the particles agglomerated into grains with a hexagonal shape. The grain size increases with the amount of Sr content, from ca. 490 nm (x = 0.0) to ca. 700 nm (x = 1.0). Room-temperature Mössbauer spectroscopy showed that the mean hyperfine field increased with the substitution of Ba2+ by Sr2+, consistent with magnetization results. The preferential sites occupied by Fe ions in the hexaferrite structure were determined. Optical studies revealed that all compounds absorb up to ca. 1000 nm, and that the bandgap energy decreases with increasing Sr content. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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30 pages, 2870 KiB  
Article
Thermal Expansion of Electrofused MgO-Based Spinel Systems Containing Fe2O3, Al2O3-Fe2O3, Al2O3-Cr2O3-Fe2O3 and Al2O3-NiO-Fe2O3
by Tilo Zienert, Otávio H. Borges, Victor C. Pandolfelli and Christos G. Aneziris
Crystals 2025, 15(3), 220; https://doi.org/10.3390/cryst15030220 - 25 Feb 2025
Cited by 1 | Viewed by 317
Abstract
Magnesia-spinel multicomponent materials have been used as refractories for a long time. In addition to a few binary systems, the influence of spinel phases on the thermal expansion (α) of MgO or the resulting compound has not been studied so far. [...] Read more.
Magnesia-spinel multicomponent materials have been used as refractories for a long time. In addition to a few binary systems, the influence of spinel phases on the thermal expansion (α) of MgO or the resulting compound has not been studied so far. As α is critical for refractories in application, this work investigates the thermal expansion of complex MgO-based spinel systems using X-ray diffraction (XRD) in combination with Rietveld refinement in the temperature range between 30 °C and 1200 °C. All studied periclase solid solutions, in contact with spinels of the systems Mg1.01(Al0.23Cr1.64Fe0.13)O4, Fe3O4–MgFe2O4, NiFe2O4–NiAl2O4, MgAl2O4–MgFe2O4, Fe3O4–FeAl2O4 and Fe3O4·NiFe2O4·2MgAl2O4 showed α trends below plain MgO, or even decreasing values above 1000 °C. Many spinels showed large negative thermal expansion coefficients. It was found that the structural change in spinels is constrained, leading to a common analytical expression to calculate the lattice parameter of spinels with temperature, which was used to study the nature of the investigated spinels in more detail. The work highlights that Cr-free MgO-spinel systems show similar or even better high-temperature behaviour than commonly used magnesia–chrome aggregates. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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11 pages, 3585 KiB  
Article
Effect of Compact Density of MoO2 Powders on Densification Kinetics and Grain Growth During Sintering Processes
by Jongbeom Lee, Jaehoon Jung, Hyowon Lee, Jaesoung Park and Haguk Jeong
Crystals 2024, 14(12), 1075; https://doi.org/10.3390/cryst14121075 - 13 Dec 2024
Viewed by 657
Abstract
MoO2 powders compacted under different uniaxial pressures ranging from 100 to 800 MPa, corresponding to the compact densities ranging from 55% to 65%, respectively, were sintered at targeted temperatures within 650–1050 °C for 1 h in an N2 atmosphere. Then, their [...] Read more.
MoO2 powders compacted under different uniaxial pressures ranging from 100 to 800 MPa, corresponding to the compact densities ranging from 55% to 65%, respectively, were sintered at targeted temperatures within 650–1050 °C for 1 h in an N2 atmosphere. Then, their densification kinetics and grain growth were investigated. With regard to the densification of MoO2 powders at room temperature, a linear relationship was observed between the compact density and log pressure in the uniaxial pressure range without fracture and local deformation. The relative densities of the sintered MoO2 samples increased with increasing compact density and sintering temperature. At a given sintering temperature, the sample with the highest compact density exhibited the best densification rate. The grain size in the sintered samples was proportional to the relative density, and the grain growth obeyed the Arrhenius equation. The sintered samples with 55%, 60%, and 65% densities during the sintering process have different activation energies values depending on the sintering temperature. At low sintering temperatures, the activation energies for 55%, 60%, and 65% compact densities were 50.8, 39.6, and 26.1 kJ/mol, respectively, and at higher sintering temperatures, the corresponding values were 19.8, 21.5, and 25.4 kJ/mol. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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12 pages, 5287 KiB  
Article
Synthesis and Characterization of TiO2 Nanotubes for High-Performance Gas Sensor Applications
by Belgacem Bouktif, Marzaini Rashid, Anouar Hajjaji, Karim Choubani, Nashmi H. Alrasheedi, Borhen Louhichi, Wissem Dimassi and Mohamed Ben Rabha
Crystals 2024, 14(11), 928; https://doi.org/10.3390/cryst14110928 - 27 Oct 2024
Cited by 1 | Viewed by 1215
Abstract
In this study, we investigated the fabrication, properties, and sensing applications of TiO2 nanotubes. A pure titanium metal sheet was used to demonstrate how titanium dioxide nanotubes can be used for gas-sensing applications through the electrochemical anodization method. Subsequently, X-ray diffraction indicated [...] Read more.
In this study, we investigated the fabrication, properties, and sensing applications of TiO2 nanotubes. A pure titanium metal sheet was used to demonstrate how titanium dioxide nanotubes can be used for gas-sensing applications through the electrochemical anodization method. Subsequently, X-ray diffraction indicated the crystallization of the titanium dioxide layer. Scanning electron microscopy and transmission electron microscopy then revealed the average diameter of the TiO2 nanotubes to be approximately 100 nm, with tube lengths ranging between 3 and 9 µm and the thickness of the nanotube walls being about 25 nm. This type of TiO2 nanotube was found to be suitable for NO2 gas sensor applications. With an oxidation time of 15 min, its detection of NO2 gas showed a good result at 250 °C, especially when exposed to a NO2 gas flow of 100 ppm, where a maximum NO2 gas response of 96% was obtained. The NO2 sensors based on the TiO2 nanotube arrays all exhibited a high level of stability, good reproducibility, and high sensitivity. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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18 pages, 1976 KiB  
Article
Influence of Process Parameters on Properties of Non-Reactive RF Magnetron-Sputtered Indium Tin Oxide Thin Films Used as Electrodes for Organic Light-Emitting Diodes
by Claudia Diletto, Fiorita Nunziata, Salvatore Aprano, Ludovico Migliaccio, Maria Grazia Maglione, Alfredo Rubino and Paolo Tassini
Crystals 2024, 14(9), 776; https://doi.org/10.3390/cryst14090776 - 30 Aug 2024
Cited by 2 | Viewed by 1266
Abstract
Indium tin oxide (ITO) is a transparent conductive oxide (TCO) commonly used in the realization of optoelectronic devices needing at least a transparent electrode. In this work, ITO thin films were deposited on glass substrates by non-reactive RF magnetron sputtering, investigating the effects [...] Read more.
Indium tin oxide (ITO) is a transparent conductive oxide (TCO) commonly used in the realization of optoelectronic devices needing at least a transparent electrode. In this work, ITO thin films were deposited on glass substrates by non-reactive RF magnetron sputtering, investigating the effects of power density, sputtering pressure, and substrate temperature on the electrical, optical, and structural properties of the as-grown films. High-quality films, in terms of crystallinity, transparency, and conductivity were obtained. The 120 nm thick ITO films grown at 225 °C under an argon pressure of 6.9 mbar and a sputtering power density of 2.19 W/cm2 without post-annealing treatments in an oxidizing environment showed an optical transmittance near 90% at 550 nm and a resistivity of 2.10×10−4 Ω cm. This material was applied as the electrode of simple-structure organic light-emitting diodes (OLEDs). Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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Review

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30 pages, 11520 KiB  
Review
Progress in Tungsten Trioxide-Based Materials for Energy Storage and Smart Window Applications
by Khursheed Ahmad and Tae Hwan Oh
Crystals 2025, 15(1), 10; https://doi.org/10.3390/cryst15010010 - 25 Dec 2024
Viewed by 765
Abstract
Previous years have witnessed a rapid surge in WO3-based experimental reports for the construction of energy storage devices (ESDs) and electrochromic devices (ECDs). WO3 is a highly electrochromic (EC) material with a wide band gap that has been extensively used [...] Read more.
Previous years have witnessed a rapid surge in WO3-based experimental reports for the construction of energy storage devices (ESDs) and electrochromic devices (ECDs). WO3 is a highly electrochromic (EC) material with a wide band gap that has been extensively used for the construction of working electrodes for supercapacitor (SC) and ECD applications. Previously, WO3-based hybrid composites were explored for SC and ECD applications. In this review report, we have compiled the WO3-based hybrid electrode materials for SC and ECD applications. It is believed that the present review would benefit the researchers working on the fabrication of electrode materials for SC and ECD applications. In this review article, challenges and future perspectives have been discussed for the development of WO3-based SCs and ECDs. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))
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