Influence Of Oxygen Vacancies Research Articles

A Bulk Oxygen Vacancy Dominating WO3−x Photocatalyst for Carbamazepine Degradation

Creating oxygen vacancy in tungsten trioxide (WO3) has been considered as an effective strategy to improve the photocatalytic performance for degrading organic pollutants. In this study, oxygen vacancies were introduced into WO3 by thermal treatment under Ar atmosphere and their proportion was changed by setting different treatment times. WO3−x samples show better photoelectric properties and photocatalytic degradation performance for carbamazepine (CBZ) than an oxygen-vacancy-free sample, and WO3−x with the optimal proportion of oxygen vacancies is obtained by thermal treatment for 3 h in 550 °C. Furthermore, it discovers that the surface oxygen vacancies on WO3−x would be recovered when it is exposed to air, resulting in a bulk oxygen vacancy dominating WO3−x (bulk-WO3−x). The bulk-WO3−x exhibited much higher degradation efficiency for CBZ than WO3−x with both surface and bulk oxygen vacancies. The mechanism study shows bulk-WO3−x mainly degrades the CBZ by producing OH radicals and superoxide radicals, while oxygen-vacancy-free sample mainly oxidizes the CBZ by the photoexcited hole, which requires the CBZ to be adsorbed on the surface for degradation. The radical generated by bulk-WO3−x exhibits stronger oxidizing capacity by migrating to the solution for CBZ degradation. In summary, the influence of oxygen vacancy on photocatalytic degradation performance depends on both the proportion and location distribution and could lie in the optimization of the photodegradation mechanism. The results of this study could potentially broaden our understanding of the role of oxygen vacancies and provide optimal directions and methods for oxygen vacancy regulation for photocatalysts.

Comprehensive investigation into the influence of oxygen vacancies on the ferroelectric properties of spin coated bismuth ferrite thin films

Abstract Bismuth ferrite (BFO) is a prime candidate for room-temperature magnetoelectric coupling and multiferroic applications. The rhombohedral R3c phase of BFO is the source of many properties, but the phase purity and oxygen vacancies are still the biggest obstacles to its real-world application. Considering these facts, the present work investigates the effects of oxygen vacancies on the functional properties through manipulation of drying temperatures of spin-cast films, especially at temperatures around 280 °C, where both the secondary phase and oxygen vacancies are prevalent. One of the biggest sources of oxygen vacancy is bismuth volatilisation and our work deals with the situation head-on uncovering the effect of bismuth volatilisation on functional properties. The structural properties were studied using X-ray diffraction (XRD), and deeper insights into the surface topography of the samples were obtained using AFM imaging. The electrical and dielectric characteristics help distinguish and analyse the samples in terms of the presence of resistive switching. PUND studies were performed to determine the ferroelectric properties of the samples. A fifty percent reduction in the oxygen vacancies in the presence of secondary phases was observed when compared with the phase-pure sample, as shown by the XPS analysis. Deeper insights were provided into the valence band spectra by first-principles studies. This work shows that phase purity may not be the singular condition for enhancing functional properties, and fine-tuning the presence of secondary phases and oxygen vacancies may be the way forward. The ferroelectric polarisation in one of the samples exhibits a notably higher value when using chemical solution deposition methods, making it a promising candidate for memory devices.

Metal exsolution from perovskite-based anodes in solid oxide fuel cells.

Solid oxide fuel cells (SOFCs) are highly efficient and environmentally friendly devices for converting fuel into electrical energy. In this regard, metal nanoparticles (NPs) loaded onto the anode oxide play a crucial role due to their exceptional catalytic activity. NPs synthesized through exsolution exhibit excellent dispersion and stability, garnering significant attention for comprehending the exsolution process mechanism and consequently improving synthesis effectiveness. This review presents recent advancements in the exsolution process, focusing on the influence of oxygen vacancies, A-site defects, lattice strain, and phase transformation on the variation of the octahedral crystal field in perovskites. Moreover, we offer insights into future research directions to further enhance our understanding of the mechanism and achieve significant exsolution of NPs on perovskites.

Influence of oxygen vacancies on the lithium-doped Mn:ZnO thin films for improved NO2 gas-sensing applications

Influence of oxygen vacancies on the lithium-doped Mn:ZnO thin films for improved NO2 gas-sensing applications

Influence of Oxygen Vacancy and Dopant in NiO Catalysts on the Selective Catalytic Reduction of NO with NH3

Influence of Oxygen Vacancy and Dopant in NiO Catalysts on the Selective Catalytic Reduction of NO with NH₃

Influence of oxygen vacancies, surface composition, and crystallite size on the photoelectrochemical oxidation activity of C,N-codoped TiO2 for cefadroxil abatement along with O3

This study aims the development of photoelectrodes to be incorporated in a photoelectrocatalytic ozonation (PECO) process for tertiary treatment of urban wastewaters, targeting the removal of contaminants of emerging concern (CEC). PECO tests were performed using urban wastewater after secondary treatment fortified with Cefadroxil (CFX, C16H17N3O5S), as target model CEC. Three Nitrogen and Carbon doped TiO2 (CN–TiO2) electrodes were synthesized by anodizing at 50, 70, and 90 V, and calcined. These materials were characterized by X-Ray diffraction and Rietveld refinement, Scanning Electron Microscopy, Diffuse Reflectance Spectroscopy, X-ray photoelectron spectroscopy, chronoamperometry, and electrochemical impedance spectroscopy, to correlate defects with photoactivity. All photoanodes considerably reduced their main bandgaps by the incorporation of C and N species, to enable absorption capacities in the UV region using a Xe lamp. The lowest oxygen vacancy content and largest crystallite size were found for CN–TiO2-70, favoring the reduction of bulk defects that could act as recombination of charge carriers. Therefore, oxygen vacancies affect more the TiO2 photoactivity compared to the crystallite size or the light absorption capacity, confirming that a lower content of vacancies in the material bulk and surface doping significantly influence the activity as detected by Rietveld refinement, DRS, and XPS. The electrochemical techniques confirm that the highest photocurrent was obtained for CN–TiO2-70, whence this photoanode was chosen to carry out the CFX degradation. A point defect model simulating Nyquist plot reveals that the photoactivity depends on the speed to diffuse oxygen vacancies through the TiO2 coating. All abatement processes were followed by high-performance liquid chromatography, and Total Organic Carbon (TOC). At neutral and alkaline conditions, CFX is eliminated to levels below the analytical detection limit after 90 min of treatment (TOC removals of 87 and 91%, respectively), indicating that the coupling between the CN–TiO2-70 photocatalyst and ozone is effective in eliminating the contaminant due to parallel routes forming •OH species. Lower CFX degradation observed at acidic pH (TOC removal of 70%) is assigned to the difficulty of oxidizing protonated CFX species.

Influence of oxygen vacancies on the performance of SnO2 gas sensing by near-ambient pressure XPS studies

Modulation of oxygen vacancy (VO··) concentrations in SnO2 is an efficient strategy for improving its NO2 sensing performance. However, due to the complex reaction process between NO2 and adsorbed oxygen species on the surface of metal oxide, the role of VO·· is still unclear without in-situ characterization. Here, SnO2 nanowires (NWs) were synthesized via chemical vapor deposition method, and the VO·· concentration in SnO2 NWs was enhanced by removing adsorbed H2O on the surface of precursor during the growth process. The VO··-abundant SnO2 NWs exhibited large improvement in NO2 sensing performance with ultralow detection limit (2 ppb NO2) and high response value towards 1 ppm NO2 (49.5 at 50 °C). Near-ambient pressure X-ray photoelectron spectroscopy was used to reveal the in-situ sensing reactions occurred on the surface of SnO2 NWs. The results revealed that VO·· provided active sites for adsorption of oxygen species and confirmed the formation of NO. This work demonstrates an easy route to grow SnO2 NW with tunable VO·· concentration, and provides a direct evidence for deeper understanding of the effect of VO·· in sensing process.

Research Trends on the Influence of Oxygen Vacancies in Post BaTiO3 (BT) Ceramics for Next-Generation MLCCs

In line with the trend towards electrification in mobility, there is a demand for the development of next-generation Multilayer Ceramic Capacitors(MLCCs) with superior properties compared to those using the conventional BaTiO<sub>3</sub> (BT) ceramics. For this, various high-performing ferroelectric ceramics have been proposed as post-BT materials, and numerous studies have been conducted on the role of oxygen vacancies within these materials. It has been confirmed that oxygen vacancies in the ceramic material have a significant impact on various properties such as oxygen ionic conduction, IR degradation, microstructure, aging degradation, and hardening effect, and by controlling the concentration and mobility of oxygen vacancies, it is possible to adjust these properties. We hope that research on the role of oxygen vacancies in various high-performing ferroelectric ceramics will be utilized as a foundation of knowledge for the development of next-generation MLCCs in the future.

Enhanced piezoelectric catalytic properties of NaNbO3 powder by defects engineering

In this work, NaNbO3 powders were prepared using a hydrothermal method. With increasing the reaction temperature, particle size of NaNbO3 unexpectedly decreases, implying the nucleation-dominated growth mechanism. The piezoelectric catalytic results indicate that the sample reacted at 210 °C for 12 h exhibits the best piezoelectric catalytic efficiency. Furthermore, NaNbO3 powders are annealed in N2 to increase the concentration of oxygen vacancy, which are demonstrated by the impedance and XPS spectra. The simulation results indicate that valence electron of A-site Na cations on the surface is easier than Nb cations to be excited to the conduction band under the influence of oxygen vacancies, which leads to more than 6 times increase in piezoelectric catalytic efficiency.

Synergetic effect of CQD and oxygen vacancy to TiO2 photocatalyst for boosting visible photocatalytic NO removal

The wide band gap of TiO2 photocatalyst material limits its application in the field of visible photocatalysis. In this paper, oxygen vacancies and carbon quantum dots (CQD) with up-conversion character were proposed to improve the photocatalytic activity for NO removal of TiO2 under visible light irradiation. The one-dimensional TiO2 nanotube (TNs), TNs containing oxygen vacancies (OVTNs), TNs of composite CQD (CQD-TNs) and OVTNs of composite CQD (CQD-OVTNs) were prepared, respectively. Furthermore, the influence of oxygen vacancies and CQD on the removal of NOx by photocatalysis were explored. It is found that CQD-OVTNs exhibits the conspicuous synergetic effect of CQD and oxygen vacancy to boost visible photocatalytic NO removal, the NO removal efficiency was about 12, 2, and 2.6 times to TNs, OVTNs and CQD-TNs. Also, CQD-OVTNs exhibits the NO2-inhibited property during the process of photocatalytic NO removal. Finally, the synergetic mechanism of CQD and oxygen vacancies to TNs for boosting visible photocatalytic NO removal was revealed.

The influence of oxygen vacancies on the optical and magnetic properties of Gd2O3/GQD nanocomposites

Gd2O3/GQD nanocomposites were successfully prepared by a one-step hydrothermal method. The oxygen vacancies induced by ultrasonic vibrations can improve the magneto-optical properties of Gd2O3/GQD nanocomposites.

Recent advances in oxygen deficient metal oxides: Opportunities as supercapacitor electrodes

Energy storage devices (ESD) are getting significant attention regarding their ability to reduce fossil fuel usage. Batteries and electrochemical supercapacitors are two well-known ESDs with supercapacitors preferred for their high energy discharge potential. The metal oxides (MOs) with robust redox characteristics are ideal candidates for supercapacitors, although their capacitance still lacks behind the theoretical values. Here, partial reduced or oxygen-deficient MOs have been identified have proven promising to reach the desired capacitance. The introduction of oxygen vacancies into MOs can effectively enhance their electrochemical properties without altering the inherent characteristics of MOs. This review discusses the recent progress on new oxygen-deficient MOs and their performance as a supercapacitor. The importance of oxygen vacancy is described, followed by the traditional synthesis route to producing MOs. The present pathways for generating oxygen vacancies and their analytical assessment are covered in-depth, followed by a section on the most advanced analytical techniques for detecting and interpreting the creation of such vacancies. The influence of oxygen vacancies on the supercapacitive performance of the most researched MOs is provided with the challenges and prospects of oxygen-deficient MOs in supercapacitor application.

High Li-ionic conductivity of Li29Zr9Nb3O40 ceramic sintered in oxygen-deficient atmosphere

Lithium ion batteries (LIBs) based on solid state electrolytes have attracted much attention for their high safety and energy density. Li29Zr9Nb3O40 powders as Li-ionic conductors were prepared using a sol-gel method in this work, and the related ceramics were sintered in air or in an oxygen-deficient atmosphere in which sample was covered with corundum crucible. All the sintered ceramics are consisted of orthorhombic phase. Li29Zr9Nb3O40 ceramic sintered in oxygen-deficient atmosphere has conductivity of 1.03 × 10−3 S cm−1 at room temperature and has ionic transference number of 0.9996, while the ceramic sintered in air has conductivity of 4.41 × 10−5 S cm−1. The influence of oxygen vacancy on the migration path of Li-ion was discussed. The migration paths of Li-ions between two kinds of Li29Zr9Nb3O40 ceramics were simulated and visualized by method of bond valence site energy with VESTA software.

Influence of oxygen vacancies on the ferromagnetism in Co-doped ZnO: An ab-initio study

Electronic and magnetic properties of cobalt doped ZnO, with and without O vacancies, were investigated using ab-initio calculations. Calculation shows that Co-doped ZnO can achieve different magnetic stable configurations as dependent on oxygen vacancy (VO) concentrations. The electronic structure illustrates that when there are VO in the structure, the ferromagnetic phase is the most stable configuration with the highest Curie temperature. Also, DOS and pDOS show that the total magnetic moment mainly consists of interaction between Co, VO, and O atoms, where the largest contributions come from the d-Co and p-O orbitals. The magnetization per Co atom shows a strong correlation with the formation energy decrease, which increases with the impurity-vacancy distance. Finally, the presence of VO results in a lower average magnetic moment per unit cell, which was also observed in the spatial spin-density distribution. These results indicate that VO in Co-doped ZnO could be the crucial key to achieve stable ferromagnetism in this diluted magnetic semiconductor with potential applications in spintronic devices.

Influence of Oxygen Vacancies and Surface Facets on Water Oxidation Selectivity toward Oxygen or Hydrogen Peroxide with BiVO4

Bismuth vanadate (BiVO4) is one of the most promising photoanode materials for water oxidation. However, the water oxidation mechanism and selectivity on the different surfaces of BiVO4 are still not well understood, partly because of the structural complexity introduced by the presence of oxygen vacancies in the material. Using density functional theory, we show that the (001) surface of BiVO4 with subsurface vacancies is the most suitable for the oxygen evolution reaction, whereas the pristine (011) surface favors the hydrogen peroxide evolution reaction. A mechanism by which the vacancies can be removed from the surface, thereby influencing the water oxidation selectivity, is also described. Our results thus emphasize the crucial impact of the local structure on the catalytic selectivity in ternary oxides.

Structure, photoluminescence, and electrical transport properties of pure and Eu2O3 activated Zn2SnO4 host matrix

In this work, crystalline Eu2O3 activated Zn2SnO4 nanoparticles were synthesized with a simple mechanosynthesis method followed by a post-heat-treatment process. Pure Zn2SnO4 (ZTO) and Eu: ZTO samples were synthesized following the same method for a comparative study. The structure and microstructure of these compounds have been characterized in detail by the Rietveld refinement method using powder XRD data and analyzing FESEM and HRTEM images. The formation of a nanocrystalline cubic Eu2Sn2O7 secondary phase is noticed in the Eu-activated compound. The influence of Eu3+ cations in the ZTO host matrix is revealed from the photoluminescence and electrical transport studies. The Eu3+ ions generate oxygen vacancy by substituting octahedral Sn4+/Zn2+ ions of the ZTO inverse spinel lattice rather than tetrahedral Zn2+ ions. It initiates optical luminescence with several intense emissions between 576 nm and 711 nm with narrowband electric dipole emissions of Eu3+ ions. The influence of oxygen vacancies on the atomic structures of the Eu:ZTO compound was revealed by the electrical transport studies and compared to pure ZTO. It is revealed that the electrical conductivity increases due to the oxygen vacancy originated by Eu3+ incorporation into the ZTO lattice. Due to superior optical property, enhanced electrical conductivity, and low dielectric constant value, the Eu:ZTO compound is appropriate for superior optoelectronic applications.

Proton-induced achiral structural transition at 180° domain wall in ferroelectrics

The influence of proton radiation on the achiral structural transition at 180° domain walls in tetragonal ferroelectric BaTiO3 is theoretically studied in this work. The proton-induced oxygen vacancy in ferroelectrics is predicted using the Monte Carlo Simulations, which increases with the increase of the proton fluence and the energy of the incident proton. A model based on the LGD is developed to investigate the influence of oxygen vacancy which is considered as a defect dipole on the achiral structural transition of Bloch–Néel type of domain wall. Under the proton radiation, the Bloch-type of domain wall shows the character of asymmetric because of the coupling of the polarization and the electric field, while the proton radiation just changes the magnitude of the polarization in the Néel-type of domain wall.

Resistive switching effect caused by oxygen vacancy migration in SrTiO3 ceramic

STO has been studied for many years and is mainly used in various fields such as ceramic capacitors, memristors and solar cells. The influence of oxygen vacancies on its physical properties is very important. In this article, we report the dielectric, impedance and current-voltage characteristics of STO ceramic at different temperatures. When the temperature is increased, the oxygen vacancy concentration of the STO ceramic increases, resulting in dielectric dispersion and dielectric relaxation behavior. In the analysis of impedance spectroscopy, oxygen vacancies mainly undergo secondary ionization and conduct grain conduction within the STO. The conductivity of STO ceramic increases with increasing temperature, mainly due to the increase in oxygen vacancy concentration. The STO ceramic at high temperature exhibits a current-voltage characteristic curve similar to the resistive switching effect, due to the migration of oxygen vacancies.

Effect of plasma power on the structural properties of tin oxide prepared by plasma-enhanced atomic layer deposition

In this study, tin oxide (SnO2) films are prepared by using plasma enhanced atomic layer deposition (PEALD) with tetrakis(dimethylamino)tin(IV) (TDMA-Sn) as the Sn metal source and O2/Ar mixture as the oxidant. The plasma power is varied from 1000 to 3000 W to investigate its influence of oxygen vacancies and defects on the SnO2 film properties. The experimental results show that the plasma power plays an important role in the deposition of SnO2 films. Unwanted Sn3O4 formation is observed at both of low and high powers. The optical emission spectra of the plasma with different power are analyzed to obtain the insight of the mechanism of the PEALD SnO2 films growth. The optimal plasma power of 1500 W is found to be very close to the threshold where the oxygen radical intensity starts to sharply increase. Lower and higher powers can lead to insufficient oxidation and strong ion bombardment, respectively, resulting in reduced SnO2 film quality.

Multiferroic and magnetoelectronic polarizations in BaFe12O19 system

Coexistence of ferroelectricity and ferromagnetism in one single phase of a solid is of great interest because of the potential application for novel electronic devices. We report on the enhanced ferroelectricity jointly co-existing with excellent magnetic performance in M-type barium hexaferrite (BaFe12O19), which demonstrating a classic electric polarization (P-E) hysteresis loop with full saturation. Two nonlinear current peaks in the I–V curve for polarization switch and giant abnormal change of dielectric constant near Curie temperatures provide sufficient experimental evidences to verify the ferroelectricity of BaFe12O19 ceramics. It holds a large remnant polarization of 55.7 μC/cm2 and a suitable coercive field at 441 kV/cm. Two peaks at 194 °C and 451 °C in the temperature-dependent dielectric spectrum of BaFe12O19 ceramics are considered to be the phase transition from ferro-to antiferro- and antiferro-to para-electric structures. A conventional strong magnetic hysteresis loop was also observed. The influence of oxygen vacancies on the band structure, electric and magnetic properties has been discussed in detail. The magnetically induced E-polarization upon the BaFe12O19 ceramics was achieved in the form of alternating spin current waves. These combined multiple functional responses of large ferroelectrics and strong ferromagnetism reveal the excellent multiferroic features of BaFe12O19, which would bring forth the great opportunity to create novel electric devices with active coupling effect between magnetic and electric orders.