Research

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15 pages, 4908 KiB

Open AccessArticle

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 509

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

Open AccessArticle

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 902

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 (Ce_1−xZr_xO₂, [...] 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 (Ce_1−xZr_xO₂, 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

Open AccessFeature PaperArticle

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

Viewed by 973

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

Open AccessArticle

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 2 | Viewed by 946

Abstract

The purpose of this paper is to assess the relationship between the core architecture of titanium(IV)-oxo complexes (TOCs) known as {Ti_aO_b} 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 {Ti_aO_b} 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

Open AccessArticle

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 974

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

Open AccessArticle

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 3 | Viewed by 1308

Abstract

The transition aluminas

δ

_{1}

and the cubic, non-spinel-type

η

-Al

_{2}

O

_{3}

were detected in addition to

α

-Al

_{2}

O

_{3}

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

δ

_{1}

and the cubic, non-spinel-type

η

-Al

_{2}

O

_{3}

were detected in addition to

α

-Al

_{2}

O

_{3}

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

-,

δ

_{1}

- and

θ

-Al

_{2}

O

_{3}

). The phases followed the expected transition sequence of

η

→

δ

_{1}

→

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

Open AccessArticle

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 1648

Abstract

Cubic zirconia (c-ZrO

_{2}

) 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-ZrO

_{2}

) 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 V

_{O}

^{2 +}

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

Open AccessArticle

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 - 08 Feb 2023

Cited by 1 | Viewed by 1444

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

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21 pages, 777 KiB

Open AccessReview

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 10 | Viewed by 2674

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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