Oxygen Defects Research Articles

Enhanced Stability Under Positive Bias Temperature Stress in Oxide Thin Film Transistors with Double Gate Structure By Improving Bottom Channel Interface

In this paper, we discuss the causes of reliability degradation in oxide TFTs with a double gate structure and propose methods for improvement. Reducing IGZO deposition power significantly improves PBTS (Positive Bias Temperature Stability) reliability in double gate structures. This improvement is attributed to reduction of excess oxygen defects accumulated at the bottom channel interface, as inferred from the difference in PBTS results for the top single gate and double gate structures

Pseudosymmetry in Tetragonal Perovskite SrIrO3 Synthesized under High Pressure.

In this study, we report a tetragonal perovskite structure of SrIrO3 (P4/mmm, a = 3.9362(9) Å, c = 7.880(3) Å) synthesized at 6 GPa and 1400 °C, employing the ambient pressure monoclinic SrIrO3 with distorted 6H structure as a precursor. The crystal structure of tetragonal SrIrO3 was evaluated on the basis of single-crystal and powder X-ray diffraction. A cubic indexing was observed, which was attributed to overlooked superlattice reflections. Weak fractional peaks in the H and K dimensions suggest possible structure modulation by oxygen defects. Magnetization study reveals weak paramagnetic behavior down to 2 K, indicative of the interplay between spin-orbit coupling, electron correlations, and the crystal electric field. Additionally, measurements of electrical resistivity display metallic behavior with an upturn at about 54 K, which is ascribed to weak electron localization and possible structural defects.

X-ray-induced long persistent luminescence of Cu+-doped high alumina borosilicate glass

A Cu+ doped high alumina borosilicate glass with long persistent luminescence (LPL) was prepared by reduction melting and radiation induction based on glass defect engineering. The maximum time of the persistent luminescence can arrive 16 h. Spectral and EPR measurements indicate that two kinds of oxygen defects can be induced by X-ray radiation. One defect was eliminated after UV irradiation, and the other can synergistically participate in the LPL process of glass with reduction induced oxygen deficiency centers(ODCs). In addition, there is a highly linear relationship between the initial LPL intensity of the glass and the radiation dose; which implies the glass can be used as a radiation detection material. The internal mechanism of the linear relationship and LPL was discussed.

Enhanced performance of photocatalytic oxidation of indoor toluene over Pd/TiO2 catalyst by tuning surface defect concentrations

An effective approach for the elimination of indoor gaseous toluene through photocatalytic oxidation involves the engineering of surface defects on catalysts. In this study, the concentrations of surface oxygen defects in PdTi-xN (x = 10, 30) catalysts were controlled using the sodium borohydride solid-phase reduction method, and their performances in the photocatalytic oxidation of indoor gaseous toluene were evaluated. PdTi–10 N demonstrated high photocatalytic efficiency for toluene oxidation, achieving 84% toluene conversion and approximately 75% CO2 mineralization. Characterization results indicated that surface oxygen defects can enhance the separation of photo-generated electrons and holes, facilitating their interaction with Pd0 species to form Ti3+ species. More reactive oxygen species (·OH-and ·O2−) were generated on PdTi–10 N due to the synergistic effect of surface oxygen defect and Ti3+ species, which played a significant role as the toluene oxidation. This work provides a new insight for the design and development of high-performance Pd/TiO2 catalysts in the field of indoor VOCs treatment.

Explore synergistic catalytic ozonation by dual active sites of oxygen vacancies and defects in MgO/biochar for atrazine degradation

The design of highly efficient and sustainable catalytic materials is highly desirable for the development of advanced oxidation process (AOPs) used in water treatment. This study used waste litchi shells as precursors to prepare biochar (BC). The composite material (BC@MgO) was synthesized upon loading magnesium oxide (MgO) on BC and used for the heterogeneous catalytic ozonation (HCO) of atrazine (ATZ). BC@MgO exhibited an ATZ degradation rate of 92.8 % over 30 min under the optimal degradation conditions and maintained its good catalytic performance over four cycles, exhibiting excellent catalytic activity and stability. Characterization and experimental results revealed the synergistic effect of oxygen vacancies (OVs) and BC defects on the adsorption and decomposition of ozone molecules. The exposure of the surface magnesium ions was promoted in the presence of OVs on MgO, allowing water molecules to dissociate on the surface magnesium sites to form surface hydrated hydroxyl groups. Biochar defects accelerated the adsorption of ozone molecules by virtue of its higher surface energy. These active sites led to the substantial generation of reactive oxygen species (ROS), which possessed strong oxidizing ability and thereby participated in the degradation of ATZ. In addition, the possible degradation pathways and toxicity of ATZ were evaluated. Overall, this design provided a novel approach to the comprehensive utilization of waste lychee shells, as well as an efficient, stable, and green catalyst for the development of AOPs used in water treatment.

Ferromagnetic property in Transition Metal (Mn, Fe, Ni)-Doped SnO2 for Spintronic Applications: A Review of Computational and Experimental Studies

The development of room temperature ferromagnetic property (RTFM) in TM doped SnO2 has potential application in the field of spintronic, recently attracted attention. This material exhibits exceptional chemical stability, demonstrates N-type behavior with a high carrier density, and remarkably displays long-range ferromagnetic properties. However, the mechanism behind this ferromagnetic property (FM) is still not fully understood. Numerous surveys of the literature have indicated that factors such as the presence of oxygen vacancies, defects, type and concentration of dopants, temperature, and methods used for sample preparation have a notable impact on the performance of FM. Here we reviewed the FM mechanism which is noticed in Iron, Nickel, Manganese doped Tin dioxide material both experimental and computational method.

Magnetic, electrochemical properties and probable mechanism of charge storage in the pristine and Cr-doped CeO2

The emergence of cerium oxide (CeO2) has garnered significant interest as an energy storage gadget owing to its inspiring electrochemical, electrical and mechanical properties. Current work, we have synthesized Ce1-xCrxO2x=0,0.025,0.05,0.1 via simple auto-combustion method. The structure–property relations were characterized by several physicochemical characterizations such as XRD, FESEM, EDAX, vibrational spectroscopy, XPS, BET and UV–visible spectroscopy. The suds-like CeO2 morphology and oxygen defects were highly suitable for the electrolytic ion intercalation to the electrode. By employing the Trassati model, Power law establishment and Dunn’s model, the innate charge storage mechanisms in the synthesized materials were revealed. The specific capacitance of pristine CeO2 attained 30.42F/g and it enhances to 73.56F/g for Ce0.925Cr0.025O2 at 0.5 A/g. Further Ce0.925Cr0.025O2 possesses a capacitance retention of 108.85 % even after 1000 GCD cycles at a current density of 4 A/g. The electrochemical results suggest Ce1-xCrxO2x=0.025 as a good material for supercapacitor applications. The magnetic measurements on the doped and undoped samples show no long-range ordering indicating zero hysteresis loss. Further, magnetic studies suggests the suitability of Ce1-xCrxO2x=0.1 for supercapacitance applications.

High-performance flexible humidity sensor based on B-TiO2/ SnS2 nanoflowers for non-contact sensing and respiration detection

The development of flexible humidity sensors is essential for the advancement of wearable devices and electronic skin. However, the process of preparing these sensors is typically complex, and they often suffer from poor stability and a limited sensing range, which fails to meet the requirements for practical applications. Here, we prepared SnS2 with nanoflower morphology by hydrothermal method, and successfully prepared a high-performance flexible humidity sensor with a high response range (20-95 %) by compositing it with B-TiO2 nanoparticles with oxygen defects after sodium borohydride reduction and coating it on a PET flexible substrate. This sensor demonstrates an exceptional response (753.2 at 90 % RH) in high humidity environments and exhibits rapid response (13 s) and recovery times (19 s). Moreover, the sensor accurately detects human breathing patterns and frequencies, making it suitable for non-contact sensing applications. This research offers valuable insights into the simplified preparation and advancement of flexible humidity sensors.

Precision engineering of surface defects of cerium oxide nanostructured fine particles for the multiplexed detection of electrolytes and glucose inside tissue models

The development of biosensors for the detection of glucose and electrolytes has become a crucial field of research nowadays due to the increasing incidence of long-term conditions. Specifically, the use of cerium oxide as a selective material for the detection of glucose is raising interest as an alternative to enzymatic sensors due to their stability and low-cost. This work demonstrates for the first time a significant improvement in the selectivity of glucose sensors based on cerium oxide nanostructured fine particles through doping with nickel ions and using pulse voltammetry for the sensing. By using nickel-doped cerium oxide fine particles, the sensitivity of the devices improved by 10-fold, and the selectivity when testing the devices against lactate increased by 68.5 % as compared to pure cerium oxide fine particles, with a limit of detection in the micromolar level. Crystallographic and compositional properties that led to such increase in sensitivity were determined, as a result of a presence of oxygen defects and amorphous domains at the surface of fine particles. This device could be adapted for the simultaneous measurement of glucose and sodium ions. The pulse voltametric approach enhanced the sensitivity of the sensors towards sodium ions, which reached a super-Nernstian sensitivity of 111 mV Log[Na+]-1, with a response time of 2 mins, and has been used for the testing of the electrodes in a practical environment using a skin-inspired material. This technology will pave the way for the development of miniaturised non-invasive wearable sensors real-time measurement of glucose and electrolytes in patients.

Construction of "Metal Defect/Oxygen Defect Junction" in ZnFe2O4-NiCo2O4 Heterostructures for Enhancing Electrocatalytic Oxygen Evolution.

Defect engineering is a promising approach to improve the conductivity and increase the active sites of transition metal oxides used as catalysts for the oxygen evolution reaction (OER). However, when metal defects and oxygen defects coexist closely within the same crystal, their compensating charges can diminish the benefits of both defect structures on the catalyst's local electronic structure. To address this limitation, a novel strategy that employs the heterostructure interface of ZnFe2O4-NiCo2O4 to spatially separate the metal defects from the oxygen defects is proposed. This configuration positions the two types of defects on opposite sides of the heterojunction interface, creating a unique structure termed the "metal-defect/oxygen-defect junction". Physical characterization and simulations reveal that this configuration enhances electron transfer at the heterostructure interface, increases the oxidation state of Fe on the catalyst surface, and boosts bulk charge carrier concentration. These improvements enhance active site performance, facilitating hydroxyl adsorption and deprotonation, thereby reducing the overpotential required for the OER.

Chemiresistive detection of xylene vapor using MOF-derived porous Co3O4 microrods activated by Mo6+ cations

Incorporation of high-valence cation into catalytic oxide (eg. Co3O4) is favorable for regulating the carrier concentration and creating more active centers for surface reaction process, thus promoting the sensing capability towards low reactive gas (eg. xylene). Herein, the metal-organic framework (MOF)-derived Mo-doped porous Co3O4 microrods are achieved through a simple solution method combing with a thermal method. The introduction of Mo6+ into Co3O4 matrix enhances the concentration of oxygen defects and Co3+, coupled with the specific surface area. As a result, the 5 at% Mo/Co3O4-based gas sensor sample exhibits a nice selectivity, clear response value (Rg/Ra=29.8 – 100 ppm), low concentration limit (0.5 ppm), and reliable stability to xylene vapor under a low working temperature (140 °C). Moreover, the possible reaction pathway (benzyl-benzaldehyde-benzoate-aromatic ester/anhydride) of xylene oxidation over this 5 at% Mo-doped Co3O4 microrod is proved by an in-situ DRIFTS analysis. Importantly, this optimized xylene-sensing capability is further discussed from the viewpoint of Mo-introducing effect into the porous Co3O4 microrods. This work further demonstrates a reliable approach of high valence cation-doped catalytic oxides to detect low reactive vapor.

Enhancing photocatalytic degradation of La-BiVO4 through bidirectional regulation of oxygen vacancy and the Mott-Schottky effect

Selective oxidation of photocatalysts is an important reaction, but catalytic capacity and reaction selectivity are usually contradictory. Herein, ultrafine La nanoparticles were introduced to regulate and control the coordination number and environment of Bi, and a catalyst was synthesized with oxygen defects (La-BiVO4) for Rhodamine degradation. Particularly, La-BiVO4 achieved a better reaction rate and selectivity under visible-light irradiation. The results revealed that the degradation rate of Rhodamine by La-BiVO4 reached 94.9 %. Additionally, the characterization and density functional theoretical calculation demonstrated that the Mott-Schottky effect in La-BiVO4 not only changed the BiVO4 electron density and boosted the visible-light-sensitivity, but also hastened the photogenerated charge migration and reduced the energy barrier. This study not only reveals the important role of optimizing single-atom coordination environment in generating free radicals in photocatalytic reactions, but also provides a reasonable degradation strategy for specific pollutants in the environment.

In-situ exsolved Ni nanoparticles for boosting CO2 reduction in solid oxide electrolysis cell

Due to their excellent high Faraday efficiency, perovskite solid oxide cells (SOECs) have attracted considerable attention. Nevertheless, they still face significant challenges in terms of stability and electrocatalytic activity during CO₂ electrolysis. In this study, Ni particles in La0.65Ba0.35Mn1-xNixO3-δ are successfully separated by a unique in-situ exsolved method of metal nanoparticles, which are uniformly anchored to the electrode surface as Ni nanometal particles. This effectively suppresses the generation of carbon deposits on the cathode surface. Under test conditions of 850 °C, 1.6 V and 50 sccm flow rate, the CO yield of the modified cathode material reached 5.9 mL min−1 cm−2, which is nearly four times higher than that before doping. The synergistic effect of in-situ exsolution of Ni metal nanoparticles with oxygen defects generated by the perovskite, creating more active locations for CO2 adsorption and electrolysis, is responsible for the significant improvement in electrochemical performance. This work provides new strategies and ideas for the development of efficient and durable SOEC cathode materials.

Coexistence of multiple magnetic interactions in oxygen-deficient V2O5 nanoparticles

This paper reports on the spin glass-like coexistence of competing magnetic orders in oxygen-deficient V2O5 nanoparticles with a broad size distribution. X-ray photoelectron spectroscopy yields the surface chemical stoichiometry of nearly V2O4.65 due to significant defect density. Temperature-dependent electrical conductivity and thermopower measurements demonstrate a polaronic conduction mechanism with a hopping energy of about 0.112 eV. The V2O5-δ sample exhibits strong field as well as temperature-dependent magnetic behaviour when measured with a SQUID magnetometer, showing positive magnetic susceptibility across the temperature range of 2-350 K. Field-cooled and zero-field-cooled data indicate hysteresis, suggesting glassy behaviour. The formation of small polarons due to oxygen vacancy defects, compensated by V4+ charge defects, results in Magneto-Electronic Phase Separation (MEPS) and various magnetic exchanges, as predicted by first-principle calculations. This is evidenced by the strong hybridisation of V orbitals in the vicinity of vacant oxygen site. An increase in V4+ defects shows an antiferromagnetic (AFM) component. The magnetic diversity in undoped V2O4.9 originates from defect density and their random distribution, leading to MEPS. This involves localised spins in polarons and ferromagnetic (FM) clusters on a paramagnetic (PM) background, while V4+ dimers induce AFM interactions. Electron paramagnetic resonance spectra measured at different temperatures indicate a dominant paramagnetic signal at a g-value of 1.97 due to oxygen defects, with a broad FM resonance-like hump. Both signals diminish with increasing temperature. Neutron diffraction data rules out long-range magnetic ordering, reflecting the composition as V2O4.886. Despite the FM hysteresis, no long-range order is observed in neutron diffraction data, consistent with the polaron cluster-like FM with MEPS nature. This detailed study shall advance the understanding of the diverse magnetic behaviour observed in undoped non-magnetic systems.

Synergistic effect of oxygen defects and calabash-like hollow carbon matrix enables VO2 as high-performance cathode for zinc ion battery

Vanadium dioxide (VO2) materials exhibit significant theoretical specific capacity, which is ascribed to multi-electron transfer reactions and unique tunneled structures. However, the low electronic conductivity and sluggish reaction kinetics of VO2 have impeded its further development. Hence, in this study, we employed a synergistic strategy of defect engineering and compositing with a calabash carbon matrix to reduce Zn2+ diffusion barriers and accelerate electron transfer. The VO2 cathode provided a high specific capacity at a low rate of 303 mA h g−1 at 0.1 A g−1 after 191 cycles, along with good rate performance (168 mA h g−1 at 10 A g−1) and satisfactory long-term stability (170 mA h g−1 at 1 A g−1 after 1100 cycles). The exhaustive structural analyses indicated that oxygen vacancies accelerated the Zn2+ diffusion rate, while a uniform calabash-like hollow carbon matrix improved electronic conductivity during cycling. Moreover, ex-situ measurements demonstrated that during discharge, the composite cathode transformed to layered Zn3+x(OH)2V2O7·2H2O, which then facilitated the subsequent intercalation of Zn2+. This cooperative strategy advances the practical application of aqueous zinc ion batteries by leveraging vanadium-based electrodes.

Effects of MOF-MoO3-x derivatives synthesis and oxygen defect engineering on photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into valuable fuels is considered a promising approach for the development of sustainable and renewable energy sources. In this study, we utilized Mo-MOF as a precursor to obtain MoO3 by pyrolytic derivatization and treated it to obtain MOF-MoO3-x containing oxygen vacancies as a catalyst for the photocatalytic reduction of CO2 to CO. MOF derivatization altered the morphology of the MoO3, which made the formation of oxygen vacancies easier and facilitated the separation of electron-hole pairs. Meanwhile, the increased specific surface area and the appearance of surface oxygen vacancies enhanced the CO2 adsorption and activation capabilities of MOF-MoO3-x. As a result, MOF-MoO3-x demonstrated a significant enhances in the photoreduction activity of CO2. Its CO yield was 29.1 μmolg−1h−1, which was 3.7 times higher than that of MOF-MoO3 and 2.4 times higher than that of H-MoO3-x. This innovative strategy may provide a new avenue for improving the comprehensive performance of photocatalysts and developing renewable energy sources.

Bi Off‐Centering in Centrosymmetric BiOBr Leading to Ultrahigh Bifunctional Piezocatalytic Fuel Generation Efficiencies in Seawater

AbstractPiezocatalytic water‐splitting to simultaneously produce H2 and H2O2 has many potential advantages. However, the necessity to utilize materials having polar structures limits the choice of piezocatalysts. Herein, it is demonstrated that centrosymmetric BiOBr with oxygen defects can simultaneously produce H2 and H2O2 with ultrahigh efficiencies from pure and seawater without needing assistance from noble metals or scavengers. High‐pressure studies confirm that there are no non‐polar‐to‐polar phase transitions in BiOBr, though a novel isostructural phase is discovered. Computational studies reveal that oxygen vacancy distorts the BiOBr structure to induce charge‐localization and polarization. Furthermore, high pressure (i) reduces carrier effective masses and (ii) increases relative O‐2p contribution in the valence band maximum to assist catalysis and improve stability. The role of oxygen vacancy is confirmed by changing its concentration, which proportionally affects H2 evolution. The work paves the way for defect engineering to develop piezocatalysts from a large pool of non‐polar materials.

(NH4)0.78V4O10-x·1.49H2O cathode with strong hydrogen bond for efficient zinc-ion storage

Layered vanadium-based compounds are promising cathode materials for aqueous zinc ion batteries (ZIBs) due to their multi-electron reactions and adjustable ion-diffusion channels. However, the narrow interplanar spacing, strong binding with Zn2+, and vanadium dissolution significantly limit their further application. Herein, we present a defective (NH4)0.78V4O10-x·1.49H2O (N2) with a strong hydrogen bond as the cathode for ZIBs. Both experimental data and DFT calculation confirm that the triple effect of intercalating H2O, increasing oxygen defects, and introducing ammonium vacancy not only enriches the active sites but also restricts the NH4+ and vanadium by strong hydrogen bonds. Meantime, the electrostatic interaction between Zn2+ and framework is also improved, both in O-free and O-defect [VOn] polyhedrons. As expected, the N2 delivers a specific capacity of 533.1 mAh g−1 (398.2 Wh kg−1 at 184.4 Wh kg−1) at 0.5 C, a rate-capability of 225.4 mAh g−1 at 20 C, and without obvious capacity decay at 20 C over 2000 cycles.

Evaporation-induced self-assembly Al doped black TiO2 for the degradation of tetracycline hydrochloride under visible light

Light absorption range, recycling stability and charge transfer efficiency are key to the performance of photocatalytic material. Based on these targets, a Al doped TiO2 catalyst was synthesized by the evaporation-induced process, after processed by NaBH4 reduction, the black TiO2 doped with Al was finally prepared. Uv-vis DRS, EPR and XPS analyses confirm the expanded light absorption window (300 nm - 1000 nm) and the introduction of abundant oxygen vacancy after the reduction process. The final product BTiO2/Al-0.5 has a degradation rate of about 84 % over the tetracycline hydrochloride within 60 minutes, the reaction rate constant (k) is 10.6 times higher than the unreduced sample. The dramatic change of photocatalytic ability can be assigned to the broadened visible light absorption, increased charge separation efficiency, narrowed band gap and defect-enriched oxygen vacancy. This work offers insights into the fabrication of TiO2 catalyst and the introduction of oxygen defect.

Tolerance of Corundum‐Structured Tin‐Doped Indium Oxide Thin Films to Gamma‐ray Irradiation

Corundum‐structured Sn‐doped indium oxide (rh‐ITO) is investigated as a novel transparent conductive oxide. Herein, its gamma‐ray tolerance up to a total dose of 77 kGy is examined for potential applications in harsh environments, such as space. The investigations are conducted on rh‐ITO with Sn concentrations of 0 and 5 at%. X‐ray diffraction 2θ‐ω scan analysis reveals that no phase separation occurs due to gamma‐ray irradiation. The carrier concentration in undoped rh‐In2O3 increases after irradiation, indicating that the gamma rays displace the oxygen atoms and form oxygen defects that generate donors. The high visible light transparency of rh‐In2O3 and rh‐ITO is maintained after irradiation. This study demonstrates the high stability of rh‐ITO to gamma‐ray irradiation until 77 kGy dose. This work contributes to the application of rh‐ITO as an electrode in high‐radiation environments.