Increase In Vacancy Concentration Research Articles

Unraveling the influence of oxygen vacancy with and without replacement on Cu<i>2</i>O: A DFT Study

This study delves into the structural and electronic effects of oxygen vacancies in Cu2O using density functional theory (DFT) enhanced with Hubbard U corrections (DFT+U). A 3x2x1 supercell of Cu2O was employed. The study meticulously investigates the removal of 1, 2, and 3 oxygen atoms, analyzing the ensuing changes in both structural stability and electronic properties, with particular emphasis on the band gap.The structural analysis revealed that oxygen vacancy formation induces significant modifications in Cu-O and Cu-Cu bond lengths, with elongations observed around the vacancy sites in which the Cu-Cu bond length decreased to 2.4035 Å, compared to 3.0066 Å in the pristine structure. The structural distortion followed the Jahn-Teller effect, leading to the formation of isolated units and transformation in bond angles. The introduction of oxygen vacancies without replacement (WOR) caused significant distortions in the Cu2O lattice, which were more pronounced with increasing vacancy concentration. The Cu-O bond length increased from 1.8492 Å in the pristine structure to 1.9840 Å in the single vacancy configuration. However, in the oxygen vacancies with replacement (WR) the Cu-Cu bond length increased slightly to 3.0218 Å, with the Cu-O bond length expanding to 1.8505 Å. The band structure analysis indicated a decrease in the band gap with increasing vacancy concentration. The pristine Cu2O exhibited a band gap of 1.67 eV as calculated, which was increased to 1.97 eV with a single vacancy and 1.16 eV with two vacancies, reflecting the significant impact of oxygen vacancies on the material’s optoelectronic properties. The findings underscore the critical role of oxygen vacancies in modulating the structural and electronic properties of Cu2O, providing insights that are pivotal for optimizing its performance in applications like photocatalysis and solar cells.

Precision tailoring strategy of oxygen vacancies for electromagnetic pollution regulation

The vacancy-dominated defect polarization plays a pivotal role in many excellent microwave absorption materials (MAMs). Here, through a straightforward annealing treatment under oxygen-deficient conditions, we successfully synthesized a series of β-MnO2 samples spanning various oxygen vacancy concentrations. Despite the absence of additional phase generation, the electromagnetic (EM) parameters of these samples displayed a notable increasing-then-decreasing trend. Chemical characterization revealed a linear increase in vacancy concentration across the samples, which contradicted the EM parameter trend, underscoring the competitive impact of oxygen vacancies in MAMs. Further examination of the electronic structure indicated that an excess of oxygen vacancies led to band gap broadening, consequently diminishing conductivity and impacting conduction loss. The optimal β-MnO2 shows an effective bandwidth of 5.4 GHz and a minimum reflection loss of −48.2 dB at a thickness of 1.7 mm. This research offers fresh perspectives on defect engineering design for MAMs, thereby contributing to the advancement of high-performance materials in the future.

Characterization of A-site doped PrBaCo2O5+δ perovskites as cathode materials for IT-SOFCs

Creating highly efficient and durable cathodes persists as a formidable task in the realm of intermediate temperature solid oxide fuel cells (IT-SOFCs). Hence, we present a double perovskite oxide, Pr0.6Sr0.4BaCo2O5+δ (PS0.4BC), and its electrocatalytic activity is thoroughly investigated. The XRD test is carried out and a notable transformation in the phase structure is observed upon the introduction of Sr2+ ions into the PBC matrix. That is, the phase structure of the material changes from double perovskite structure to single perovskite structure. Through the TG and TEC test that the introduction of Sr2+ ions into the lattice can create additional sites for oxygen vacancy formation and reduce TEC values. Further verify that Sr doping can enhance the concentration of oxygen vacancies of the material. The PS0.4BC cathode material exhibits remarkably low polarization resistance, achieving an impressive value of 0.027 Ω cm2 at an operating temperature of 800 °C. Oxygen partial pressure test shows that as the oxygen partial pressure decreases, there is a notable increase in impedance, particularly evident in the low frequency region of the Nyquist plots. This indicates that the oxygen content has obvious effects on the low-frequency processes. When the oxygen partial pressure exceeds 0.05 atm, the oxygen adsorption-dissociation and diffusion process is the rate-limiting step in the ORR. However, when the oxygen partial pressure is less than 0.05 atm, the formation of lattice oxygen through the combination of oxygen ions and oxygen vacancies processes is the rate-limiting step. Compared PBC cathode material, the more pronounced changes in the high frequency arc of the PS0.4BC cathode at the same oxygen content. It shows that Sr doping significantly changes the high frequency process. After doping, the oxygen vacancy concentration increases, which facilitates the occurrence of the charge transfer process at high frequency.

Defect design and vacancy engineering of NiCo2Se4 spinel composite for excellent electromagnetic wave absorption

Vacancy engineering presents an appealing method for modifying the electronic structure of spinel architectures. However, based on well-defined vacancy concentrations, how to design anionic vacancies to modulate electromagnetic parameters as well as electromagnetic wave absorption (EMA) properties is less studied. Here, NiCo2Se4 spinel structures were prepared using different selenization methods, and the Se vacancy defect concentration was controlled by changing the annealing temperature, thus regulating the EMA properties. Among them, the design of the hollow structure effectively enhanced the EMA performance. Moreover, the increase of Se vacancy concentration increases the conductivity loss while regulating the electronic structure, and also acts as an unsaturated site to induce the formation of dipoles to optimize the polarization loss. The effective absorption bandwidth (EAB) of NiCo2Se4-130 reaches 8.48 GHz at 2.4 mm at the highest Se vacancy concentration. This work establishes a direct relationship between vacancy concentration and the electromagnetic wave dissipation capability, offering valuable insights for the development of advanced EMA materials.

Zn-substituted Co3O4 crystal anchored on porous carbon nanofibers for high performance supercapacitors

Metal-organic frameworks (MOFs) are a promising class of electrode materials for supercapacitors. In this work, MOF-derived transition metal oxide/carbon nanofiber composites (ZnCoO/C) are synthesized through a freeze-drying method followed by a carbonization process. The crystal structure of the ZnCoO/C product is regulated by changing the ratio of Co to Zn, which in turn influences its electrode properties. The electrochemical tests reveal that the ZnCoO/C-2 electrode demonstrates an impressive specific capacitance of 356.3 F g-1 at 1 A g-1 and maintains a capacitance retention exceeding 77 % after 10,000 cycles, which exhibits a good cycling stability. It is found that appropriate Zn substitution can diminish the crystallinity of the material, augment the active sites, and enhance the specific capacitance of the electrode material. Considering the heteroatom substitution tends to introduce vacancy defects in the crystals, this work theoretically explores the effect of oxygen vacancies on the electrode materials. As the oxygen vacancy concentration increases, the band gap and the adsorption energy of the models decrease; conversely, the formation energy of the models shows an increasing tendency. This indicates that an increase in oxygen vacancies can enhance the electrical conductivity of electrode materials and facilitate their kinetic process but destroy the stability of crystal. This research explores the interplay between the microstructure and the electrochemical performance of electrode materials, providing a foundational reference for the design of structurally optimized high-performance electrodes and further elucidating the energy storage mechanisms in supercapacitors.

Phonon transport in vacancy induced defective stanene/hBN van der Waals heterostructure

In this study, Non-Equilibrium Molecular Dynamics (NEMD) simulation is employed to investigate the phonon thermal conductivity (PTC) of Sn/hBN van der Waals heterostructures with different vacancy-induced defects. We deliberately introduce three types of vacancies in Sn/hBN bilayer point vacancies, bivacancies, and edge vacancies at various concentrations ranging from 0.25% to 2%, to examine their effects on PTC across temperatures from 100 K to 600 K. The key findings of our work are (i) PTC declines monotonically with increasing vacancy concentration for all types of vacancies, with a maximum reduction of ∼62% observed at room temperature compared to its pristine form. (ii) The position of defects has an impact on PTC, with a larger decrease observed when defects are present in the hBN layer and a smaller decrease when defects are in the Sn layer. (iii) The type of vacancy also influences PTC, with point vacancies causing the most substantial reduction, followed by bivacancies, and edge vacancies having the least effect. A 2% defect concentration results in a ∼62% decrease in PTC for point vacancies, ∼51% for bivacancies, and ∼32% for edge vacancies. (iv) Finally, our results indicate that for a given defect concentration, PTC decreases as temperature increases. The impact of temperature on thermal conductivity is less pronounced compared to the effect of vacancies for the defective Sn/hBN bilayer. The presence of vacancies and elevated temperatures enhance phonon-defect and phonon–phonon scattering, leading to changes in the phonon density of states (PDOS) profile and the distribution of phonons across different frequencies of Sn/hBN bilayer, thus affecting its thermal conductivity. This work offers new insights into the thermal behavior of vacancy-filled Sn/hBN heterostructures, suggesting potential pathways for modulating thermal conductivity in bilayer van der Waals heterostructures for applications in thermoelectric, optoelectronics, and nanoelectronics in future.

Fe-Doped SrCoOx FET Sensors for Extreme Alkaline pH Sensing.

The accurate measurement of pH in highly alkaline environments is critical for various industrial applications but remains a complex task. This paper discusses the development of novel Fe-doped SrCoOx-based FET sensors for the detection of extreme alkaline pH levels. Through a comprehensive investigation of the effects of Fe doping on the structure, electrical properties, and sensing performance of SrCoOx, we have identified the optimal doping level that significantly enhances the sensor's performance in highly alkaline conditions. With a Fe doping level of 5 mol %, the sensitivity of the sensor improves to 0.86 lg(Ω)/pH while maintaining the response rate. Further increasing the Fe doping to 10 mol % results in a sensor that demonstrates favorable response time, a suitable pH range, and a linear correlation between lg(R) and pH. The combination of X-ray photoelectron spectroscopy and X-ray diffraction analysis provides insight into the regulation mechanisms of Fe doping on the crystal structure, electronic structure, and oxygen vacancy concentration of SrCoOx. Our findings indicate that Fe doping leads to an increase in oxygen vacancy concentration and a decrease in the energy barrier for oxygen ion migration, which contributes to the improved sensing performance of the Fe-doped SrCoOx sensors. Additionally, the study highlights the influence of oxygen vacancy concentration on the electrical properties of SrCoOx. Precise control over the concentration of oxygen vacancies is crucial for optimizing the sensitivity and response speed of SrCoOx FET sensors under extreme alkalinity conditions.

Octahedron vacancy induced luminescence improvement of double perovskite type phosphors LaMg2/3-xNb1/3O3:Mn4+ with multifunctional applications

Near infrared (NIR) phosphors have been booming as promising candidates for agriculture due to the adjustable spectrum and excellent match with the dyes of the plants. Here, Mn4+ activated double perovskite LaMg2/3Mn1/3O3 NIR phosphor was prepared, which showed high match with the absorption spectra of phytochrome PFR. Concentration of Mg2+ was decreased to create octahedron vacancy into the lattice to improve the luminescence performance. Structure and luminescence variation of the phosphors LaMg2/3-xNb1/3O3:Mn4+ along with the increased vacancy concentration were carried out. Relative sensitivity Sr of the optimized LaMg0.57Nb0.33O3:Mn4+ reaches 3.109 % and exhibits great application potential in temperature sensor. Both the NIR light emitting diode (LED) and white LED were fabricated by using this double perovskite NIR phosphor and applied to the cultivation of dragon fruit as light compensation. The dragon fruits matured faster than those without any light compensation. These results confirm the great application potential of this double perovskite NIR phosphor in temperature sensor and plant cultivation.

Quasi-Van der Waals Epitaxial Growth of γ'-GaSe Nanometer-Thick Films on GaAs(111)B Substrates.

GaSe is an important member of the post-transition-metal chalcogenide family and is an emerging two-dimensional (2D) semiconductor material. Because it is a van der Waals material, it can be fabricated into atomic-scale ultrathin films, making it suitable for the preparation of compact, heterostructure devices. In addition, GaSe possesses unusual optical and electronic properties, such as a shift from an indirect-bandgap single-layer film to a direct-bandgap bulk material, rare intrinsic p-type conduction, and nonlinear optical behaviors. These properties make GaSe an appealing candidate for the fabrication of field-effect transistors, photodetectors, and photovoltaics. However, the wafer-scale production of pure GaSe single-crystal thin films remains challenging. This study develops an approach for the direct growth of nanometer-thick GaSe films on GaAs substrates by using molecular beam epitaxy. It yields smooth thin GaSe films with a rare γ'-polymorph. We analyze the formation mechanism of γ'-GaSe using density-functional theory and speculate that it is stabilized by Ga vacancies since the formation enthalpy of γ'-GaSe tends to become lower than that of other polymorphs when the Ga vacancy concentration increases. Finally, we investigate the growth conditions of GaSe, providing valuable insights for exploring 2D/three-dimensional (3D) quasi-van der Waals epitaxial growth.

Performance improvement of oxygen electrode in reversible protonic ceramic electrochemical cell by co-doping of La and F

Reversible protonic ceramic electrochemical cell (R-PCEC) has demonstrated high potential as an energy storage and conversion device. Efforts have primarily concentrated on the development of oxygen electrodes being to increase their performance and reduce performance degradation. In this work, three perovskite materials, namely Ba0.9Co0.2Fe0.7Nb0.1O3-δ (BCFN), Ba0.8La0.1Co0.2Fe0.7Nb0.1O3-δ (BLCFN), and Ba0.8La0.1Co0.2Fe0.7Nb0.1F0.1O2.9-δ (BLCFNF) are investigated. Both doping with La and co-doping with La and F lead to a notable reduction in the average valence states of Fe, Co, and Nb elements, further resulting in an increase in oxygen vacancy concentration, thereby enhancing the oxygen migration ability of the material. The H2O partial pressure does not have a significant impact on the polarization resistance (Rp) of the oxygen electrode. Conversely, the rise in Rp is highly correlated with the decrease in oxygen partial pressure, suggesting that the primary factor influencing the reaction rate of the oxygen electrode process is the exchange of oxygen ions on the surface of the electrode. BLCFNF exhibits the best oxygen migration and surface exchange ability, resulting in the lowest Rp. When BLCFNF was used as the oxygen electrode in a R-PCEC with the humidity air (10%H2O) and humidified H2 (3%H2O) as oxidant and fuel, respectively, it exhibits the highest maximum power density of 472 mW cm−2, and a current density of −682.6 mA cm−2 (1.3 V) at 650 °C. In addition, BLCFNF also shows good durability in both discharge and electrolysis process. The results indicate that La and F co-doped BLCFNF material is a promising oxygen electrode material for R-PCECs.

Boosting photocatalytic performance in Cu doped ZnO nanocomposites: Investigation of exciton-free carrier conversion and oxygen vacancy dynamics

The production of photocatalytic materials with strong light absorption ability and high quantum efficiency by simple means is a long-term goal of photocatalytic technology. In this work, we have synthesized Cu doped ZnO nanoparticles by a facile sol-gel method. By introducing Cu impurities, it is shown that the excitons in ZnO have been efficiently separated into free carriers, leading to optimized photocatalytic performance. The surface amorphous layers of the nanoparticles grew thicker at the introduction of Cu atoms into ZnO lattice, which boosted the photocatalytic ability due to the increase of surface oxygen vacancy concentration. This finding provides a direct evidence of quasi-particle-free carrier conversion in Cu doped ZnO, as well as a guidance for fabricating high efficiency ZnO based nano-photocatalysts.

Enhanced electrochemical performance of (PrBa)xFe1.9Nb0.1O5+δ symmetrical electrodes with A-site deficient for symmetrical solid oxide fuel cells

Symmetrical solid oxide fuel cells (SSOFCs) with symmetrical electrodes have many desirable characteristics compared with conventional SOFCs. However, the lack of electrode materials simultaneously satisfied the high electrocatalytic activity in oxidizing and reducing atmospheres. Herein, a novel perovskite oxide electrode (PrBa)xFe1.9Nb0.1O5+δ ((PB)xFN, x = 1, 0.97, 0.95 and 0.93) was reported as a promising symmetrical electrode material for SSOFCs. XRD results reveal that the (PB)0.95FN sample has a tetragonal structure and good chemical compatibility with Gd0.1Ce0.9O2-δ electrolyte. Among all the samples, (PB)0.95FN has the lowest polarization resistance (Rp). At 800 °C, compared with primary PBFN, the cathode Rp of (PB)0.95FN is reduced from 0.109 Ω cm2 to 0.063 Ω cm2 in air, whereas the anode Rp is decreased from 0.3808 Ω cm2 to 0.3109 Ω cm2 in H2. In addition, an electrolyte-supported single cell with (PB)0.95FN symmetrical electrodes achieves a maximum peak power density at 800 °C, which is enhanced by 14.67 % compared with that of PBFN. A-site deficiency on PBFN perovskite shows better electrochemical performance, which is attributed to an increase in oxygen vacancy concentration. The results indicate that (PB)0.95FN is a potential electrode material for SSOFCs.

Optimizing Low-Temperature CO2 methanation with Aluminum-Doped Ni/CeO2 Catalysts: Insights into reaction pathway adjustments and strong Metal-Support interactions

Revealing the logical relationship between the structure, reaction mechanism and performance of the catalyst is a key step in the design of low-temperature CO2 methanation catalyst. The elemental Al was introduced into Ni/CeO2 using a co-precipitation method to form a composite support CeO2-Al2O3 loaded nickel-based catalyst. It was found that the incorporation of Al significantly improved the catalytic performance of low-temperature CO2 methanation. Notably, at a molar ratio of Al/Ce equal to 0.1, the catalyst exhibited optimal CO2 conversion of 88.83% and CH4 selectivity of 99.96% at 240 ℃. The addition of appropriate amounts of Al not only increases the specific surface area of the catalyst but also maintains a moderate strong interaction between metal Ni-support, thereby promoting the formation of active metal Ni species. Furthermore, the presence of Al leads to an increase in oxygen vacancy concentration, which facilitates the generation of numerous hydroxyl groups. Consequently, this alters the distribution of basic sites on the catalyst surface, resulting in a shift from the CO* pathway to a dual pathway involving both CO* and formate pathways. Remarkably, these divergent reaction pathways correspond to distinct active sites, thereby maximizing the utilization of each region within the catalyst. The diversity of reaction pathways and active sites represents pivotal factors for enhancing the catalytic performance of low-temperature CO2 methanation catalysts.

Effect of microwave heating on the interdiffusion in BaTiO3–SrTiO3 binary ceramic system

An investigation on the effect of microwave heating (2.45 GHz) on the interdiffusion process was carried out and compared with conventional heating for BaTiO3–SrTiO3 binary system in the temperature range of 1200–1400 °C. Interdiffusion coefficients were extracted using Boltzmann–Matano analysis for both heating methods. Consequently, microwave heating was determined to result in higher interdiffusion coefficients compared to conventional heating. Correspondingly, ∼27% decrease in the apparent activation energy of interdiffusion was found which was associated with faster diffusion under electromagnetic irradiation due to increased vacancy concentration and more open lattice structure in Ba-rich regions which could be exploited for unique experimentations and non-equilibrium/non-stoichiometric phase transformations to study their kinetics and formation mechanisms and grasp a better understanding on the dielectric properties of such perovskites.

Correlation of electronic structure and magnetic properties of [formula omitted] nanostructure using synchrotron soft XAS

The present study reports crystalline structure, electronic structure and magnetic properties for nanoparticles undoped CeO2 and Ce1-xSmxO2 (x = 0.02 to 0.10, @ 0.02). The nanoparticle samples are synthesized by the co-precipitation method. XRD data shows the successful incorporation of Sm3+ ions at Ce4+ sites in the face-centered cubic (fcc) lattice. The soft X-ray absorption spectroscopy technique is utilized to get an insightful overview of electronic structural properties due to structural defects, chemical states and the development of oxygen vacancies in Ce1-xSmxO2 nanoparticles. The soft XAS spectra show a significant Ce and Sm peak in the M4,5 domain, along with the well-defined O K-edge peak. Analysis of Ce M4,5-edges indicates that Ce-ions have both 3 + and 4 + oxidation states. With the incorporation of Sm+3 ions, there is a reduction of Ce4+ states and oxidation of Ce3+ states, as well as a substantial increase in oxygen vacancy concentration. The room-temperature magnetic properties of Ce1-xSmxO2 nanoparticles reveal ferromagnetic behavior. The origin of ferromagnetism is explained by F-center exchange (FCE) coupling mechanisms mediated via development of oxygen vacancy and defects.

Effect of oxygen vacancy of lignite-char-supported Co catalysts doped with In on efficient dry reforming of methane

In this study, a series of catalysts rich in oxygen vacancies were prepared through the introduction of indium (In) for application in the dry reforming of methane. Among these catalysts, one doped with 2 wt% In, named as Co-2In/C, showcases a higher surface area (417 m2/g) and smaller particle size (4.21 nm). The stability assessment for Co-2In/C catalysts conducted under conditions of 800 °C, 0.5 MPa and a flow rate of 30,000 mL·h−1·g-1cat over 100 h resulted in CH4 and CO2 conversions of 73 % and 83 %, respectively, and a ratio of H2/CO is 0.65 without evident deactivation. The generation of more oxygen vacancies balances the redox capability of the catalyst and prevents excessive metal agglomeration. Moreover, an increase in oxygen vacancy concentration accelerates carbon elimination and extends the catalyst life.

Enhancing sintering behavior and conductivity of YSZ electrolyte by co-doping of ZnO and MnO2

This study aimed to enhance the sinterability and conductivity of yttria fully stabilized zirconia electrolyte through co-doping by 2 mol% of ZnO and different contents of MnO2 (0, 0.5, 1, 1.5 mol%) at two sintering temperatures of 1300 and 1400 °C. Phase composition identification, density, microstructure, and conductivity of the samples were evaluated using X-ray diffraction (XRD), Archimedes' method, field emission scanning electron microscopy (FESEM), and electrochemical impedance spectroscopy (EIS), respectively. The XRD results revealed that ZnO and MnO2 are successfully doped in the fluorite structure of YSZ sintered at 1400 °C, and the cubic structure is completely preserved. However, at a sintering temperature of 1300 °C, the (111) peaks of doped samples were slightly split, which implied a slight phase transformation of YSZ from cubic to a tetragonal structure. The co-doped samples, at both sintering temperatures, showed higher relative density and grain size compared with pure YSZ. The addition of 2 mol% of ZnO and 0.5 mol% of MnO2 at 1400 °C increased the relative density of YSZ from 81.6% to 95.1%. The increase in relative density and grain size, while maintaining the cubic structure, caused an increase in the conductivity of the mentioned sample. Compared with pure YSZ, the sample's total conductivity increased from 7.37 to 10.03 S m−1 at 800 °C. The proposed composition showed better sintering behavior, lower activation energy of grain conductivity, and higher conductivity than pure YSZ. This behavior is thought to be due to the facilitating rearrangement of atoms during sintering and an increase in oxygen ion vacancy concentration due to co-doping with the appropriate amount of ZnO and MnO2.

Facile Deficiency Engineering in a Cobalt-Free Perovskite Air Electrode to Achieve Enhanced Performance for Protonic Ceramic Fuel Cells.

As a crucial component responsible for the oxygen reduction reaction (ORR), cobalt-rich perovskite-type cathode materials have been extensively investigated in protonic ceramic fuel cell (PCFC). However, their widespread application at a commercial scale is considerably hindered by the high cost and inadequate stability. In response to these weaknesses, the study presents a novel cobalt-free perovskite oxide, Ba0.95La0.05(Fe0.8Zn0.2)0.95O3-δ (BLFZ0.95), with the triple-conducting (H+|O2-|e-) property as an active and robust air electrode for PCFC. The B-site deficiency state contributes significantly to the optimization of crystal and electronic structure, as well as the increase in oxygen vacancy concentration, thus in turn favoring the catalytic capacity. As a result, the as-obtained BLFZ0.95 electrode demonstrates exceptional electrochemical performance at 700 °C, representing extremely low area-specific resistance of 0.04 Ω cm2 in humid air (3 vol.% H2O), extraordinarily high peak power density of 1114mW cm-2, and improved resistance against CO2 poisoning. Furthermore, the outstanding long-term durability is achieved without visible deterioration in both symmetrical and single cell modes. This study presents a simple but crucial case for rational design of cobalt-free perovskite cathode materials with appreciable performance via B-site deficiency regulation.

The effect of micromechanical stresses on vacancy formation and stress-driven mass-transport in polycrystalline Fe–Au alloy

In recent years, a new class of super saturated binary and ternary alloys have demonstrated the ability for the self-healing of creep-induced voids formed at the grain boundaries. However, a clear understanding of the parameters affecting the self-healing mechanism is still not yet complete. One of the main challenges is understanding the effect of microstructure and micromechanical stresses on the redistribution of the healing-solute and vacancies. To this end, we address this issue using a CALPHAD-informed diffusion model coupled with crystal plasticity. In principle, the approach is general and can be used for any binary Fe–X alloy, but in this work Fe–Au binary system is used since it experimentally showed the best healing efficiency. First, we present a multicomponent diffusion model considering cross and stress-driven diffusion. The effect of stress was also considered on the equilibrium vacancy concentration. To investigate the effect of the micromechanical stresses, a representative volume element (RVE) was obtained using the phase-field method. The results showed that the maximum vacancy concentration is at the grain boundaries (GBs) with the highest hydrostatic tensile stresses. These were also the regions of the highest Au enrichment. A crucial factor to achieve this is the high diffusivity of Au compared to the Fe matrix. Increasing the stresses, lead to an increase both in vacancy and Au concentration. The accompanying increased stress triaxiality is suggested to be the reason for the reduced self-healing efficiency observed in previous experimental studies.

An oxygen vacancy-rich BiO2-x/COF heterojunction for photocatalytic degradation of diclofenac.

A BiO2-x/COF composite was successfully synthesized by simple mechanical ball milling. Compared to pure BiO2-x and COFs, the BiO2-x/COF composite (1 : 9) showed superior photocatalytic capability. Under visible light irradiation for 90 min, the photocatalytic degradation rate of DCF reached 97%. In addition, the characterization results showed that the formation of heterojunctions and the increase in oxygen vacancy concentration were the reasons for the enhancement of the photocatalytic activity. It is confirmed by free radical capture experiments that ˙O2- and h+ are the main reactive substances in the photocatalytic process. The photocatalytic degradation mechanism of the composite and the photocatalytic degradation pathway of diclofenac were deduced.