Increase In Concentration Of Oxygen Vacancies Research Articles

Regulation of oxygen vacancy concentration over ZnCr oxide in bifunctional catalyst for the direct conversion of syngas to light olefins

Metal oxides play a crucial role in catalytic activity of bifunctional catalyst for directly converting syngas into light olefins. A series of ZnCr oxides were synthesized with varying concentrations of precipitant and different atmospheres of precipitate treatment via co-precipitation method. The characterization results indicate that suitable concentration of precipitant and hydrogen calcination contribute to the generation of more oxygen vacancies that can promote the chemical adsorption of CO. Density function theory calculations confirmed that the adsorption energy of CO could be decreased with increasing concentration of oxygen vacancies, and that the formation energy of oxygen vacancies was lower under the hydrogen atmosphere as compared to the oxygen atmosphere. The catalytic activity demonstrated that more oxygen vacancies promoted the chemisorption and conversion of CO. The ZnCr oxide obtained through hydrogen calcination exhibited the highest concentration of oxygen vacancy and achieved a C2=-C4= selectivity of 86 % and a CO conversion of 43 % at 4 MPa and 5400 mL g−1h−1 combined with SAPO-34 zeolite. These findings suggest that increasing oxygen vacancy concentration on the surface of metal oxides is an effective approach for designing high-performance catalysts for directly converting syngas into light olefins.

Oxygen Vacancies Mediated Co‐Sputtered Ti‐Doped BiVO4Thin Films‐Based Transparent Photovoltaic Device

AbstractBiVO4, a narrow bandgap material (2.5 eV), has been widely explored for photocatalytic applications, but its applications in the optoelectronic field are unexplored. This work explores BiVO4for photovoltaic devices using the oxygen vacancies mediated co‐sputtered Ti‐doped BiVO4(Ti:BiVO4) that exhibits on‐site power production by photovoltaics and see‐through features. The structural, chemical, and optical properties of Ti:BiVO4 are investigated for heterojunction formation with p‐type NiO film. The sputtering power of Ti plays a significant role in improving the light absorption capability by increasing oxygen vacancy concentration, enhancing the device performance. The devices show an open‐circuit voltage value of 676 mV and a short‐circuit current density value of 4.83 mA cm−2with a maximum power production value of 122.2 µW under UV illumination of intensity 53.1 mW cm−2. The obtained device performances correlate with the Ti dopant's deposition power that tunes the structural and optical properties of BiVO4films. Moreover, in self‐powered mode, the fabricated devices show a fast photoresponse speed of 0.8 ms with a high detectivity value of 2.22 × 1012Jones. This work establishes the suitability of co‐sputtered Ti:BiVO4for the next generation of transparent self‐powered optoelectronic devices.

Mn dopant-enabled BiFeO3 with enhanced magnetic and photoelectric properties

In this study, BiFe1−XMnXO3 (BFMXO, x = 0, 0.03, 0.05, 0.07, 0.10, and 0.15) nanoparticles were synthesized using the sol-gel technique. The XRD patterns confirm that the BFMXO nanoparticles exhibit a rhombic structure with the addition of Mn dopant, while structural distortion occurred as the doping concentration increased. In particular, Mn doping effectively induced lattice shrinkage and enhanced the lattice strain. The SEM and TEM images showed increased uniformity and grain size reduction as Mn doping concentration increased. The XPS spectra show that the conversion of Fe2+ to Fe3+ leads to the increase of oxygen vacancy concentration. Further, the M−H loops show that the saturation magnetization and residual magnetization of all Mn-doped samples were successfully improved with the gradual transformation from antiferromagnetism to ferromagnetism. Therefore, BiFe0.93Mn0.07O3 reached a maximum Ms and Mr of approximately 0.956 and 0.054 emu/g, respectively. Further, BiFe0.93Mn0.07O3 exhibited 4–5 times higher photoconductivity than the pristine sample. First-principles calculations further accounted for the improved magnetic and electrical properties of BFMXO induced by the Mn dopant. This study demonstrates an effective method for controlling the structure and characteristics of BFO-based nanomaterials for multifunctional device applications.

Preloaded oxygen vacancy conditioning Ni/TiO2 to enhance photocatalytic CO2 reduction

The regulation of oxygen vacancy (OV) defects plays a critical role in facilitating photocatalytic reactions. In this study, Nix/TiO2-OV photocatalytic materials with ultra-high oxygen vacancy concentrations (>33%) were prepared by preloading oxygen vacancies on Ni/TiO2 system. The experimental results show that the catalytic performance initially rises and subsequently declines with an increase in oxygen vacancy concentration. Among the samples, the best one (8Ni/TiO2-OV2) exhibits a noteworthy photocatalytic yield of CO (22.654 μmol·g−1·h−1) and CH4 (3.93 μmol·g−1·h−1). Density functional theory (DFT) shows that the excellent catalytic performance of 8Ni/TiO2-OV2 is due to that oxygen vacancy is in favour of the narrowing of the band gap, thereby promoting the excitation and efficient transfer of electrons. This study presents a promising novel method for obtaining ultra-high concentration of oxygen vacancies and explores the relationship between oxygen vacancy concentration and catalytic performance.

Impact of Bottom Electrode in HfO2-Based Rram Devices on Switching Characteristics

Resistive random-access memory (RRAM) devices with hydrogen plasma treated HfO2 have shown low power switching (1) and good conductance quantization with programing pulsed operation (2) that qualify them to be used for in-memory computing. Engineering the distribution of defects or oxygen vacancies near the top and bottom electrodes has a significant impact on reducing the switching power and improving the multi-level cell (MLC) characteristics of the device. A graded distribution with higher concentration of oxygen vacancies closer to the top electrode (TE) due to hydrogen plasma treatment and lower concentration near the bottom electrode (BE) reduces switching energy (power) (1). However, the impact of the bottom electrode is not well understood. In this work we investigated three RRAM stacks as shown in Figure 1 that have the same top electrode metal (50nm PVD TiN/5nm ALD TiN) and dielectric (HfO2 with hydrogen plasma treatment at the mid-point) but with different BE for each stack: TiN (device A (control)), TiN plus Mo with thermal anneal (device B), and TiN plus Mo with plasma nitridation (device C). Choosing a more inert metal as the BE provides a lower oxygen vacancy concentration at the interface between the BE and the dielectric (3) which in turn reduces the switching power as noted with device C (TiN plus Mo with plasma nitridation) which switches at a minimum compliance current (Icc) of 500pA. It is possible that the presence of nitrogen prevents the increase in oxygen vacancy concentration near the BE. On the other hand, a higher concentration of oxygen vacancies at the BE and the dielectric interface leads to a larger magnitude of band bending and increases the height of Schottky barrier. This possibly leads to an increase in the switching power in device A and device B as compared to device C (3-4). Note that device A (TiN) switched at Icc=30µA and device B (TiN plus Mo with thermal anneal) switched at Icc=8µA, which is superior compared to device A in switching power. This suggests that the alloy of TiN with Mo is reducing the oxygen vacancies near the BE. To study the MLC characteristics of the devices, we performed a train of 36 RESET pulses with fixed amplitude Vp= -1V and pulse width starting at 4µs and increasing by 20µs every 3 pulses, while we applied Vr=0.1V and tr=10µs after each pulse to measure the conductance. Figure 2 shows that device B (TiN plus Mo with thermal anneal) has good MLC with no overlap between the states while device A shows unstable MLC behavior due to time constant variation. Figure 3a shows the results of device C for the same RESET pulse train that was applied to devices A and B. Since device C switches at very low current and voltage, the conductance quantization was unstable after 15 pulses due to overstress of the conductive filament. Figure 3b shows the results after selecting the proper pulse set Vp= -0.5V and pulse width starting at tp=100ns and increasing by 100ns every 3 pulses, while we applied Vr=0.05V and tr=100ns after each pulse, resulting in a better conductance quantization compared to the previous setup. Appropriate engineering of the BE and managing of the oxygen vacancy distribution by hydrogen plasma treatment can significantly reduce the switching power.

Electrochemical activity of copper doped Sr2.7Pr0.3Fe2O7−δ cathode catalysts for solid oxide fuel cells

Due to their great efficiency, low cost and pollution, and flexible fuel choice, solid oxide fuel cells (SOFCs) have been applied to energy conversion filed. However, one challenge for developing SOFCs is sluggish oxygen reduction reaction (ORR) rate. Herein, a series of Ruddlesden-Popper-type Sr2.7Pr0.3Fe2–xCuxO7–δ (SPFCx) oxides are successfully synthesized and thoroughly assessed as potential SOFCs cathodes. Among all compositions, Sr2.7Pr0.3Fe1·9Cu0·1O7–δ (SPFC10) possesses the best electrocatalysis performance and improved oxygen reduction kinetics, with the lowest polarization resistance (Rp, 0.13 Ω cm2) at 700 °C. Cu-doping will contribute to improving oxygen transport kinetics, increasing oxygen vacancy concentration, and O 2p band centers close to the Fermi level, hence, enhancing the electrocatalysis performance. At 700 °C, the maximum output of the single cell with SPFC10 cathode is 704 mW cm−2. These results highlight a highly active SPFC10 cathode with Ruddlesden-Popper structure for SOFCs.

Chemiresistive room temperature NO2 sensor based on nitrogen doped zinc oxide nanowires

The prevalence of nitrogen dioxide (NO2) in the atmosphere is causing a steady increase in air pollution. As such, there is an urgent need to create a sensitive and energy-efficient NO2 gas sensor to ensure environmental and health safety. In this study, we explore the effectiveness of nitrogen-doped zinc oxide nanowires in detecting harmful NO2 gas. Through the hydrothermal method, we synthesized zinc oxide (NW-0) and nitrogen-doped zinc oxide nanowire sensors (NW-1, NW-2 & NW-4). The introduction of nitrogen induced changes in both the crystallite size and nanowire density in ZnO. Additionally, an increase in oxygen vacancy concentration was observed with nitrogen doping. At room temperature, the NW-2 sensor exhibited exceptional NO2 sensing performance (response of 110) compared to NW-0 sensor (response of 1.9) for 10 ppm of gas. The NW-2 sensor also demonstrated a rapid response/recovery time of 50 s/5 s for a 10 ppm NO2 concentration. Moreover, the sensor showed stability over an extended period, minimal response variation with changes in relative humidity, and selectivity towards NO2 over other gases. Complementing the experimental findings, density functional theory (DFT) calculations were employed to estimate the adsorption energies of NO2 on the sensor surface.

Analyzing the role of Ni dopant to change the structural, optical and photocatalytic properties of SnO2 nanoparticles

SnO2 and 5 wt% Ni doped SnO2 nanoparticles (SnO2:Ni NPs) were successfully synthesised by a template-free hydrothermal method. X-ray diffraction (XRD) patterns depicted polycrystalline nature of the NPs in rutile-type cassiterite phase with dominant (110) and (101) Bragg diffraction peaks. Rietveld refinement of XRD patterns supported single phase tetragonal crystal structure having space group P42/m n m. With Ni doping, crystallite size of NPs decreased from 39 nm to 35 nm whereas lattice strain increased from 3.56 × 10−3 to 3.99 × 10−3. This is attributed to the substitution of Sn4+ ion by Ni2+ ions. The morphology of the SnO2 NPs also changed from regular spherical shape to elongated irregular shape upon Ni doping. The dominant Raman peak obtained at 634 cm−1 matched with the signature peak for rutile SnO2 (Raman A1g mode). Further, we observed disappearance of E g mode due to Ni doping, which indicated the formation of oxygen vacancies. Also, XPS analysis indicated an increase of oxygen vacancy concentration in the doped NPs due to charge imbalance between Sn4+ and Ni2+. The direct optical band gap of SnO2 increased from 3.97 eV to 4.11 eV when doped with 5 wt% Ni and it is ascribed to Burstein–Moss effect. Irrespective of higher optical band gap of SnO2:Ni NPs, they showed enhanced photocatalytic activity to degrade Rhodamine B (RhB) dye molecules under UV-visible irradiation. The first order kinetic reaction rate constants for degradation of RhB were found to be 0.014 min−1 and 0.045 min−1 in case of SnO2 and SnO2:Ni NPs respectively. The enhanced photocatalytic activity in SnO2:Ni NPs is explained by relating to the formation of more oxygen vacancies and chemisorptions of O2 and H2O molecules followed by generation of radicals. This work demonstrates the superiority of SnO2:Ni NPs for use as photocatalytic material for industrial waste water treatment.

Enhanced oxygen reduction reaction activity and electrochemical performance of A-site deficient (La0.6Sr0.4)1-xFe0.8Ni0.2O3−δ cathode for solid oxide fuel cells

In this work, (La0.6Sr0.4)0.9Fe0.8Ni0.2O3-δ (LSFN90), a stable, highly ORR-active and cost-efficient perovskite oxide, is developed as cathode materials for solid oxide fuel cell (SOFC). The introduction of A-site deficiency results in the crystal expansion of the cubic perovskite phase and an increase in oxygen vacancy concentration at operating temperature. The LSFN90 cathode displays good oxygen reduction reaction activity and low polarization resistance values. The A-site deficiency facilitates the diffusion of oxygen ions in the electrode and accelerates the surface oxygen exchange reaction. LSFN90 is used as cathode materials for SOFC to prepare anode-supported single cells, achieving maximum power densities of 1.51, 1.27, 0.95 and 0.63 W cm−2 under wet hydrogen (3%H2O–97%H2) atmosphere at 850, 800, 750 and 700 °C, respectively. The introduction of A-site deficiency can greatly enhance the oxygen reduction reaction activity and electrochemical performance of the cathode, demonstrating that LSFN90 has significant potential as a cathode material for practical applications in solid oxide fuel cells.

Enhanced performance of La1-xFeO3-δ oxygen carrier via A-site cation defect engineering for chemical looping dry reforming of methane

Chemical looping is a process-intensification tool that focuses on the fields of fossil fuel combustion, CO2 capture, hydrocarbon valorization, energy storage, and other energy-related and environmental-related areas. Perovskite-structured LaFeO3, a typical oxygen storage material, shows great potential for chemical looping partial oxidation and H2O/CO2 splitting. Here, we report a simple and efficient strategy to enhance catalytic activity by tuning A-site cation defects in perovskites via a sol-gel method. Systematically studies show that A-site cation defects affect both the physical and chemical properties. With the A-site cation defect engineering, the crystallite size of the La1-xFeO3-δ perovskites is reduced. The catalytic performance for CH4 oxidation and CO2 splitting is enhanced with increasing oxygen vacancy concentration. The La0.93FeO3-δ oxygen carrier exhibits the highest catalytic performance with 88% CO selectivity and 90% methane conversion at 750 °C. In addition, the La0.93FeO3-δ shows higher stability in the successive CH4 partial oxidation/CO2 splitting redox cycles, with almost unchanged CH4 conversion and CO selectivity. All these results demonstrate that the strategy of adjustment of different molar ratios of A/B site in perovskite metal oxides can effectively regulate the oxygen vacancy concentration.

Resistive-type sensors based on few-layer MXene and SnO2 hollow spheres heterojunctions: Facile synthesis, ethanol sensing performances

High-performance and low-cost gas sensors are highly desirable and involved in industrial production and environmental detection. The combination of highly conductive MXene and metal oxide materials is a promising strategy to further improve the sensing performances. In this study, the hollow SnO2 nanospheres and few-layer MXene are assembled rationally via facile electrostatic synthesis processes, then the SnO2/Ti3C2Tx nanocomposites were obtained. Compared with that based on either pure SnO2 nanoparticles or hollow nanospheres of SnO2, the SnO2/Ti3C2Tx composite-based sensor exhibits much better sensing performances such as higher response (36.979), faster response time (5 s), and much improved selectivity as well as stability (15 days) to 100 ppm C2H5OH at low working temperature (200 °C). The improved sensing performances are mainly attributed to the large specific surface area and significantly increased oxygen vacancy concentration, which provides a large number of active sites for gas adsorption and surface catalytic reaction. In addition, the heterostructure interfaces between SnO2 hollow spheres and MXene layers are beneficial to gas sensing behaviors due to the synergistic effect.

3R-IrO2 Two-Dimensional Nanosheets with Varying Layer Spacing and [IrO6] Distortion for OER

Here, two iridium-based crystal structures, K0.3IrO2·xH2O and Rb0.3IrO2·xH2O, have been synthesized for application in the oxygen evolution reaction (OER). The 3R-type layered IrO2 structures with different lattice parameters were successfully obtained from the two Ir structures by the hydrogen ion exchange method. According to synchrotron radiation spectra and the theoretical calculation of density functional theory (DFT), the increase of oxygen vacancy concentration caused by lattice distortion in the 3R-IrO2 crystal is negatively correlated with the activity of OER. A high concentration of oxygen vacancies will reduce Ir–O hybridization, which is not conducive to the balance between the adsorption and desorption of intermediate products. The higher OH adsorption energy barrier and band gap of the 3R-IrO2 crystal limited the improvement of electrochemical performance. In addition, through the analysis of the bonding orbitals and antibonding orbitals of the two structures, we concluded that 3R-IrO2 belongs to the nonthermodynamically stable structure and is not suitable for hydrogen production by electrolysis of water.

Oxygen Vacancy and Valence Band Structure of Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0-0.15) with Enhanced ORR Activity for IT-SOFCs.

The oxygen reduction reaction (ORR) activity of a Cu-doped Ba0.5Sr0.5FeO3-δ (Ba0.5Sr0.5Fe1-xCuxO3-δ, BSFCux, x = 0, 0.05, 0.10, 0.15) perovskite cathode was investigated in terms of oxygen vacancy formation and valence band structure. The BSFCux (x = 0, 0.05, 0.10, 0.15) crystallized in a cubic perovskite structure (Pm3¯m). By thermogravimetric analysis and surface chemical analysis, it was confirmed that the concentration of oxygen vacancies in the lattice increased with Cu doping. The average oxidation state of B-site ions decreased from 3.583 (x = 0) to 3.210 (x = 0.15), and the valence band maximum shifted from -0.133 eV (x = 0) to -0.222 eV (x = 0.15). The electrical conductivity of BSFCux increased with temperature because of the thermally activated small polaron hopping mechanism showing a maximum value of 64.12 S cm-1 (x = 0.15) at 500 °C. The ASR value as an indicator of ORR activity decreased by 72.6% from 0.135 Ω cm2 (x = 0) to 0.037 Ω cm2 (x = 0.15) at 700 °C. The Cu doping increased oxygen vacancy concentration and electron concentration in the valence band to promote electron exchange with adsorbed oxygen, thereby improving ORR activity.

Unveiling positive impacts of fluorine anion doping on extraordinary catalytic activity of bifunctional-layered double perovskite electrodes for solid oxide fuel cells and electrolysis cells

To address the impacts of anion doping, F-doped layered double perovskites (Pr1.1Ba0.9Co2O5+δFx) have been synthesized, demonstrating bifunctional activity in both solid oxide fuel cell and solid oxide electrolysis cell models. The F doping induces increased oxygen vacancy concentration and enhanced electrical conductivity. Combined with spherical aberration-corrected transmission electron microscopy and X-ray photoelectron spectroscopy analyses, the F− anions are successfully introduced into the host lattice, promoting the oxygen surface exchange/diffusion rates. From the density functional theory calculations, the covalence between Co 3d and O 2p-orbital is enlarged in the F-doped model, and both oxygen reduction reaction and oxygen evolution reaction activities are improved. The area-specific resistance of the Pr1.1Ba0.9Co2O5+δF0.1 (P1.1BCOF0.1) electrode is as low as 0.033 Ω/cm2 at 700 °C. The P1.1BCOF0.1 cathode-based fuel cell delivers a peak power density of 1102 mW/cm2, along with an excellent operating stability at 700 °C. Moreover, the current density of 1335 mA/cm2 is achieved in the P1.1BCOF0.1 anode-based electrolysis cell at 1.8 V toward CO2 reduction reaction at 750 °C. These results here highlight the performance origin and bifunctional activity of fluorine-doped perovskite materials, which may help us rationally design the oxide catalysts.

Crystal and Electronic Structure of Oxygen Vacancy Stabilized Rhombohedral Hafnium Oxide.

Hafnium oxide is an outstanding candidate for next-generation nonvolatile memory solutions such as OxRAM (oxide-based resistive memory) and FeRAM (ferroelectric random access memory). A key parameter for OxRAM is the controlled oxygen deficiency in HfO2-x which eventually is associated with structural changes. Here, we expand the view on the recently identified (semi-)conducting low-temperature pseudocubic phase of reduced hafnium oxide by further X-ray diffraction analysis and density functional theory (DFT) simulation and reveal its rhombohedral nature. By performing total energy and electronic structure calculations, we investigate phase stability and band structure modifications in the presence of oxygen vacancies. With increasing oxygen vacancy concentration, the material transforms from the well-known monoclinic structure to a (pseudocubic) polar rhombohedral r-HfO2-x structure. The DFT analysis shows that r-HfO2-x is not merely epitaxy-induced but may exist as a relaxed compound. Furthermore, the electronic structure of r-HfO2-x as determined by X-ray photoelectron spectroscopy and UV/Vis spectroscopy corresponds very well with the DFT-based prediction of a conducting defect band. The existence of a substoichiometric (semi-)conducting phase of HfO2-x is obviously an important ingredient to understand the mechanism of resistive switching in hafnium-oxide-based OxRAM.

Phase evolution and enhanced room temperature piezoelectric properties response of lead-free Ru-doped BaTiO3 ceramic

Abstract Recent years have witnessed considerable work on the development of lead-free piezoelectric ceramic materials and their structure–property correlations. The development of piezo response is a strong function of phase evolution in these materials. In this work, we report the effect of Ru doping and consequent phase evolution on the maximization of piezoelectric response of polycrystalline lead-free barium titanate, depicted as Ba(RuxTi1-x)O3 (BRT). The samples were prepared in a narrow compositional range of 0 ≤ x ≤ 0.03 using the conventional solid-state reaction method. Ru doping increases the leakage current of BaTiO3 samples attributed to increased oxygen vacancy concentration due to substitution of Ti4+ by Ru3+. Detailed structural analysis reveals that samples exhibiting coexistence of tetragonal (space group: P4mm) and orthorhombic (space group: Amm2) structured phases near room temperature reveal relatively enhanced piezoelectric properties. The BRT sample with Ru content of 2 mol% yields a maximum longitudinal piezoelectric coefficient, d33 of ∼269 pC/N, a high strain value of 0.16% with a large remnant polarization of ∼19 µC/cm2 and a coercive field of 5.8 kV/cm. We propose that the ‘4d’ orbital of Ruthenium plays a crucial role in improving the functional properties and in decreasing the ferroelectric Curie temperature. Our work provides clues into tailoring the phase evolution for designing lead-free piezoelectric materials with enhanced piezoelectric properties.

La0.3Sr0.7Ti0.3Fe0.7O3-δ-Based Electrodes for Symmetrical Solid Oxide Fuel Cells by A-Site Deficiency Manipulation

Solid oxide fuel cells (SOFC) with symmetric configuration have received widespread attention for their potential immunity toward resisting coking and sulfur poisoning. A key requirement for electrodes in the development of symmetric solid oxide fuel cells is the high electrocatalytic activity in both oxidizing and reducing atmospheres. Herein we report a facile method to improve the electrochemical performance of La0.3Sr0.7Ti0.3Fe0.7O3-δ- (LSTF-) based perovskite electrode material by introducing the deficiency in the A-site. X-ray diffraction (XRD) results demonstrated that A-site deficient LSTF exsolves a small amount of Fe0 metallic particles and layer perovskite Sr2TiO4, which exhibits high electrical conductivity in H2 atmosphere, while at the same time the exsolution is reversible. The polarization resistances (Rp) of (La0.3Sr0.7)0.95Ti0.3Fe0.7O3-δ (LSTF-5%) are 0.032 and 0.110 Ω cm2 in air and wet H2 (containing 3% H2O), respectively, at 800 °C. The power density of the electrolyte-supported SSOFCs with LSTF-5% as symmetrical electrode reaches up to 431.8 mW cm–2 at 800 °C in wet H2/air. And the LSTF-5% symmetrical cell also exhibits excellent electrochemical performance and high stability for electrochemically reducing pure CO2. Therefore, LSTF-5% perovskite can act as an excellent electrode material in a symmetrical SOFC. The results in this paper also indicate that an appropriate amount of A-site deficiency on LSTF perovskite can lead to an increase in oxygen vacancy concentration and better electrochemical performance.

Hierarchical porous NiO doped ZnO nanocomposite for formaldehyde gas sensor with high sensitivity, fast response/recovery and good selectivity

Formaldehyde (HCHO) is a kind of indoor pollution gas which seriously harms human health. High properties gas sensor for formaldehyde are essential for indoor air quality monitoring. The development of new nanostructured composites as gas sensing materials is seen as a viable way to improve sensing performance. In this study, a new type of layered porous nickel oxide doped zinc oxide nanocomposite with sunflower straw as a template (SFS NiO/ZnO) was synthesised. The structure and morphology of the material was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These results exhibit that the synthetic SFS NiO/ZnO successfully maintains the original pore morphology of the sunflower straw material and the framework consists of a large number of nanoparticles of uniform size and shape. The gas sensing performance of the prepared samples was tested and the results showed that the SFS NiO/ZnO biocomposite had promising sensing performance for formaldehyde. The response of the SFS NiO/ZnO gas sensor working at 240 °C was 42 for 100 ppm formaldehyde with response and recovery times of 9 s and 8 s, respectively. The lower limit of detection is 148 ppb. Compared with SFS ZnO, the significant improvement of formaldehyde sensing properties could be attributed to its increased oxygen vacancy concentration and the presence of p-n type heterojunctions.

First-Principles Study on Mechanical and Optical Behavior of Plutonium Oxide under Typical Structural Phases and Vacancy Defects.

The chemical corrosion aging of plutonium is a very important topic. It is easy to be corroded and produces oxidation products of various valence states because of its 5f electron orbit between local and non-local. On the one hand, the phase diagram of plutonium and oxygen is complex, so there is still not enough research on typical structural phases. On the other hand, most of the studies on plutonium oxide focus on PuO2 and Pu2O3 with stoichiometric ratio, while the understanding of non-stoichiometric ratio, especially for Pu2O3-x, is not deep enough. Based on this, using the DFT + U theoretical scheme of density functional theory, we have systematically studied the structural stability, lattice parameters, electronic structure, mechanical and optical properties of six typical high temperature phases of β-Pu2O3, α-Pu2O3,γ-Pu2O3, PuO, α-PuO2,γ-PuO2. Further, the mechanical properties and optical behavior of Pu2O3-x under different oxygen vacancy concentrations are analyzed and discussed in detail. The result shows that the elasticity modulus of single crystal in mechanical properties is directly related to the oxygen/plutonium ratio and crystal system. As the number of oxygen vacancies increases, the mechanical constants continue to increase. In terms of optical properties, PuO has the best optical properties, and the light absorption rate decreases with the increase of oxygen vacancy concentration.

Effect of gadolinium addition on the corrosion behavior and oxide properties of titanium in boric acid solution at 50 °C

The purpose of this study is to investigate the electrochemical and immersion corrosion behavior of Ti-5 wt.% Gd alloy in a boric acid solution at 50 °C. The chemical states and defect densities of oxide films formed in the solution were determined using X-ray photoelectron spectroscopy and the Mott–Schottky relation, respectively. Ti-5Gd alloy revealed a higher corrosion and passive current density, and greater weight loss compared to pure Ti, which is primarily attributed to the preferential dissolution of anodic Gd-rich particles in the cathodic Ti matrix. Incorporation of Gd3+ ions into the TiO2 lattice increased oxygen vacancy concentration; therefore, the oxide films of Ti-5Gd alloy contained much more point defects that carry the charges through the films, thereby deteriorating the corrosion resistance of the alloy in regards to the properties of the films.