Double Oxide Research Articles

Author Correction: Quantification of DNA double strand breaks and oxidation response in children and adults undergoing dental CBCT scan

Author Correction: Quantification of DNA double strand breaks and oxidation response in children and adults undergoing dental CBCT scan

Corrosion Ferritic Stainless Steel in a Simulated Hydrothermal Liquefaction Bioconversion Aqueous Solution: Effect of Surface Cr Content

Abstract The objective of this study was to determine the effect of surface Cr content on the corrosion of ferritic stainless steels in hot pressurized alkaline water (310 °C at 10 MPa) simulating a hydrothermal liquefaction bioconversion medium. Two methods to increase the Cr surface content were investigated: (i) selecting commercial grades of ferritic stainless steel with an increasing Cr content and (ii) applying a Cr coating (chromizing) to a low-Cr (Type 409) ferritic stainless steel. The observed parabolic-like corrosion kinetics were analyzed and discussed in terms of the structure and composition of the double layered oxide films that formed. The (surface) Cr content is a critical factor affecting corrosion. Corrosion was reduced by 66% (after 20 days exposure) when increasing the Cr content from 9 wt.% (P91) to 21 wt.% (SS443) in the commercial grades of ferritic stainless steel. Moreover, corrosion was reduced by 84% (after 20 days exposure) by chromizing the surface of a low-Cr (Type 409) ferritic stainless steel. Improved corrosion protection was attributed to increased Cr incorporation into the inner (barrier) Fe(Fe1-nCrn)2O4 layer, with the formation of a Cr2O3 layer (resulting from chromizing) being most beneficial.

Preparation and Properties of Fe-Based Double Perovskite Oxide as Cathode Material for Intermediate-Temperature Solid Oxide Fuel Cell

Double perovskite oxides with mixed ionic and electronic conductors (MIECs) have been widely investigated as cathode materials for solid oxide fuel cells (SOFCs). Classical Fe-based double perovskites, due to their inherent low electronic and oxygen ionic conductivity, usually exhibit poor electrocatalytic activity. The existence of various valence states of B-site ions modifies the material’s catalytic activity, indicating the possibility of the partial substitution of Fe by higher-valence ions. LaBaFe2−xMoxO5+δ (x = 0, 0.03, 0.05, 0.07, 0.1, LBFMx) is used as intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode materials. At a doping concentration above 0.1, the Mo substitution enhanced the cell volume, and the lattice expansion caused the formation of the impurity phase, BaMoO4. Compared with the parent material, Mo doping can regulate the oxygen vacancy concentration and accelerate the oxygen reduction reaction process to improve the electrochemical performance, as well as having a suitable coefficient of thermal expansion and excellent electrode stability. LaBaFe1.9Mo0.1O5+δ is a promising cathode material for IT-SOFC, which shows an excellent electrochemical performance, with this being demonstrated by having the lowest polarization resistance value of 0.017 Ω·cm2 at 800 °C, and the peak power density (PPD) of anode-supported single-cell LBFM0.1|CGO|NiO+CGO reaching 599 mW·cm−2.

Observation of Griffiths phase and giant magnetocaloric effect in double perovskite oxide RE2FeCrO6 (RE = Gd, Tb, Dy, Er)

AbstractThe magnetic properties of double perovskite oxide RE2FeCrO6 (RE = GD, Tb, Dy, Er) were systematically studied, and the Griffiths phase evolution was observed. In Tb2FeCrO6, Dy2FeCrO6, and Er2FeCrO6, there are antiferromagnetic (AFM)‐ferromagnetic (FM) first‐order phase transition and the Griffiths phase with coexistence of FM and paramagnetic (PM) was observed by the EPR spectra. Gd2FeCrO6 has an AFM–PM second‐order phase transition, and there is no first‐order phase transition in the range of ∆H = 0–50 kOe. As the temperature decreases, all four sets of samples present χ−1 (T) deviates downwards from the Curie–Weiss linear behavior from 0.2 to 5 kOe, corresponding to the typical characteristics of Griffiths phase evolution. In addition, all four sets of samples have excellent magnetocaloric performance. Especially, the Gd2FeCrO6 oxide has giant magnetic entropy change and relative cooling power (−∆SMmax = 30.31 J/kg K and RCP = 312.8 J/kg when ∆H = 50 kOe). From the perspective of low‐temperature magnetic refrigeration application, the present work provides important candidate references for magnetic component researchers.

Evolution of metallicity, enhancement of [formula omitted] and magnetic anisotropy energy in Y[formula omitted]NiIrO[formula omitted]: Hydrostatic ([111]) strain influence

Ir-based double perovskite oxides (DPO) provide a distinct electronic and magnetic behavior due to entanglement among lattice distortion, strong electron correlation, and spin–orbit coupling (SOC). In this work, we investigated the hydrostatic ([111]) strain impact on the physical properties of the Y2NiIrO6 DPO using ab-initio calculations. Unstrained motif displayed the ferrimagnetic (FiM) spin state owing to strong antiferromagnetic (AFM) interactions between Ni↑ and Ir↓ ions, further confirmed by the computed partial spin magnetic moments and 3D spin-magnetization density iso-surfaces plots. A Mott-insulating state is established with an energy band gap (Eg) of 0.43 eV due to the existence of a rare Ir+4 state having Jeff.=12 and a Curie temperature (TC) of 198 K using the Heisenberg Hamiltonian model, which is up to the experimental observations. The easy magnetic axis is the [010] (b-axis) having a giant magnetic anisotropy energy (MAE) constant of 1.7 × 108 erg/cm3. Moreover, it is predicted that strain holds the FiM spin order as a magnetic ground state for the considered range of ±8%. Notably, an electronic transition from Mott-insulating to a metallic state is established at a critical compressive strain of −8%, where the admixture of Ir 5d states appears at/around the Fermi level. On the other hand, Eg solely increases with the increase of tensile strain amplitude. Due to strong and weak hybridization, the spin/orbital magnetic moment value is reduced and enhanced as a function of compressive and tensile strains, respectively. Along with this, it is found that MAE/TC increases to 25%/18% and 15%/10% at −8% compressive and ＋8% tensile strains due to larger structural distortion than that of the unstrained one, which enhances the system potential for magnetic memory devices.

First principles investigation of structural, electronic, optical, transport properties of double perovskites X2TaTbO6 (X= Ca, Sr, Ba) for optoelectronic and energy harvesting applications

Structural, electrical, optical, thermoelectric response of X2TaTbO6 (X = Ca, Sr, Ba) double perovskites oxides are studied by using WIEN2k that is based on quantum mechanical calculations employing PBE-GGA approximation under the framework of DFT. We present electronic attributes including band gaps and density of states, and explain the electronic properties of all three oxide double perovskite materials which proved that they belong to directly forbidden band gap materials family. The cubic compounds Ba2TaTbO6, Sr2TaTbO6, and Ca2TaTbO6 have respective direct band gaps of 2.35 eV, 2.15eV, and 2.25 eV. Optical conductivity σ(ω), reflection R(ω), complex dielectric constants, refractive index ƞ(ω), absorbance α(ω), loss parameter L(ω) and extinction coefficient K(ω) are all utilized to explore light dependent characteristics of studied compounds. Thermoelectric parameter like, Number of Seebeck effect (S), charge carrier (n), magnetic susceptibility, power factor (PF), electrical conductivity (σ/t), thermal conductivity K/t, and heat capacity are key characteristics for materials to study its ability of thermal behavior. These thermoelectric parameters were determined by using BoltzTraP code. By studying the numbers on various material properties, scientists are uncovering new possibilities for creating sustainable materials for sustainable gadgets.

High-performance cellulose acetate fibers-loaded Al ca layered double oxide adsorbents towards efficient elimination of anionic pollutants: Mechanism adsorption and RSM-CCD approach

High-performance cellulose acetate fibers-loaded Al ca layered double oxide adsorbents towards efficient elimination of anionic pollutants: Mechanism adsorption and RSM-CCD approach

Novel sol-gel derived layered double oxides and layered double oxide/γ-Al2O3 with tunable selectivity as promising adsorbents for L-lactate uptake from the myoblast culture medium

Cultured meat production, a biotechnological solution for global protein demand and sustainability, faces economic challenges due to the high demand for cell culture medium. Contamination with cell metabolites, particularly L-lactate, impedes myoblast proliferation in high-density suspension culture. Eliminating L-lactate is crucial for reusing the medium and overcoming economic barriers in mass myoblast culture. Retaining essential nutrients like D-glucose, amino acids, and vitamins after L-lactate removal is imperative for sustained myoblast growth. This study proposes a sustainable and economically feasible adsorption technique utilizing novel sol-gel derived Mg-Al layered double oxides and Mg-Al layered double oxide/γ-Al2O3 with tunable selectivity as a promising tool for L-lactate uptake from the myoblast medium. In an aqueous solution, L-lactate uptake and selectivity over D-glucose were enhanced with the decrease in total Mg/Al ratio and crystallinity, increase in Al2O3 dispersion in adsorbent, specific surface area, and porosity. The latter was achieved successfully by metal alkoxide sol-gel method employing an organic structure-directing agent, where LDO/amorphous alumina nanohybrid with Mg/Al = 1.23 was successfully prepared in mixed methanol-ethanol solution in a relatively short time. A simple mixture of Mg-Al LDO with Mg/Al = 2 and nano-γ-Al2O3 prepared by a sustainable and economically feasible co-precipitation method was found to have comparable efficiency and selectivity to a costly sol-gel derived material. In myoblast medium, lower total Mg/Al was associated with higher cytocompatibility, pH-stability, and selectivity, while surface properties of materials did not play a significant role. Nano-γ-Al2O3 was identified as the most promising material for selective L-lactate uptake from the myoblast culture medium. Thus, further optimization of the medium treatment process with nano-γ-Al2O3 can realize cost-effective high-density myoblast culture with circular use of the medium – a novel sustainable process in the biotechnology field.

A Short Review of Layered Double Oxide-Based Catalysts for NH3-SCR: Synthesis and NOx Removal

Nitrogen oxides are one of the main atmospheric pollutants and pose a threat to the ecological environment and human health. Selective catalytic reduction (NH3-SCR) is an effective way of removing nitrogen oxides, with the catalyst being the key to this technology. Two-dimensional nanostructured layered double oxide (LDO) has attracted increasing attention due to the controllability of cations in the layers and the exchangeability of anions between layers. As a derivative of layered double hydroxide (LDH), LDO not only inherits the controllability and diversity inherent in the LDH structure but also exhibits excellent performance in the catalytic field. This article contains three main sections. It begins with a brief discussion of the development of LDO catalysts and analyzes the advantages of the LDO structure. The later section introduces the synthesis methods of LDH, clarifies the conversion relationship between LDH and LDO, and summarizes the modification impacts of the properties of LDO catalysts. The application of LDO catalysts used in NH3-SCR under wild temperature conditions is discussed, and the different types, reaction processes, and mechanisms of LDO catalysts are described in the third section. Finally, future research directions and outlooks are also offered to assist the development of LDO catalysts and overcome the difficult points related to NH3-SCR.

A‐site Regulated (PrBa)xCo1.5Fe0.5O6‐δ Double Perovskite Oxides: Highly Active and Durable Electrocatalysts for the Enhanced Oxygen Evolution Reaction

Oxygen evolution reaction (OER) represents a significant bottleneck in many energy technologies such as electrochemical water splitting, metal‐oxygen (O) batteries, and solid oxide fuel cells (SOFCs), because of the complexity of the reaction process. Double perovskite oxides (ABO3), recognized for their compositional flexibility, have emerged as excellent OER activity and stability. This study investigates the catalytic potential of B‐site ordered double ABO3 with (PrBa)xCo1.5Fe0.5O6‐δ (PBCF‐x, x=0.9‐1.1) in alkaline media. The results reveal that PBCF‐0.9, characterized by an A‐site deficient composition, exhibits exceptional OER activity. It demonstrates a low Tafel slope of 76.12 mV⋅dec‐1 and a low overpotential (η) of 270 mV at 10 mA⋅cm‐2. Notably, the intrinsic OER activity of PBCF‐0.9 is 25% higher than that of the stoichiometric PBCF‐1.0. Additionally, PBCF‐0.9 exhibits remarkable durability, as evidenced by its stable performance during a 6‐hour chronopotentiometry (CP) test and minimal microstructural changes. These results underscore the effectiveness of A‐site deficiency in optimizing the structure of double ABO3 for improved OER performance. This approach presents a promising strategy for designing highly efficient, stable, and inexpensive catalysts for energy‐related applications.

Role of Cerium-Layered Double Hydroxide-Derived Oxide Dopants in Vanadium Phosphorus Oxide for Selective Oxidation of n-Butane

Role of Cerium-Layered Double Hydroxide-Derived Oxide Dopants in Vanadium Phosphorus Oxide for Selective Oxidation of <i>n</i>-Butane

Affinity peptide-based electrochemical biosensor with 2D-2D nanoarchitecture of nickel–chromium-layered double hydroxide and graphene oxide nanosheets for chirality detection of symmetric dimethylarginine

The accurate assessment of kidney dysfunction is crucial in clinical practice, necessitating the exploration of reliable biomarkers. However, current methods for measuring SDMA often fall short in terms of sensitivity and specificity. In this study, we employed phage display technology to identify high affinity peptides that specifically bind to SDMA. The selected peptide was subsequently integrated into a novel Ni-Cr layered double hydroxide-graphene oxide (NCL-GO) nanoarchitecture. We characterized the electrochemical properties of the biosensor using cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry, systematically evaluating critical parameters such as limit of detection (LOD), reproducibility, and performance in complex biological matrices including urine. The NCL-GO architecture not only enhances the surface area available for electrochemical reactions but also facilitates rapid electron transfer kinetics which are essential for the accurate quantification of small molecule, SDMA. The electrochemical biosensor exhibited an outstanding limit of detection of 0.1 ng/mL in the 0–1 ng/mL range and 7.2 ng/mL in the 1–100 ng/mL range, demonstrating exceptional sensitivity and specificity for SDMA. Furthermore, the biosensor displayed excellent reproducibility with a relative standard deviation of 4.9%. Notably, it maintained robust chirality sensing capabilities, even in complex biological fluids. These findings suggest that this biosensor could play a pivotal role in early disease diagnosis and therapeutic monitoring, ultimately improving clinical outcomes and advancing biomedical research.

Enhanced phosphorus adsorption performance of ZnAl-LDO by fluorine‑chlorine co-doping and synergistic mechanism exploration

Layered double hydroxides (LDHs) and their calcined products layered double oxides (LDOs) are widely used as adsorbents for pollutant removal. Their adsorption performance are significantly influenced by intercalated ions, while previous studies primarily focusing on the impact of individual ions. For the first time, this paper reports the mechanism of the synergistic enhancement of phosphate adsorption properties of LDO by bicomponent interlayer ions. The ZnAl-LDO by fluorine‑chlorine co-doping (F, Cl-ZnAl-LDO) exhibits excellent adsorption capacity of 158.9 mgP/g, surpassing that of single-component intercalation Cl-ZnAl-LDO and F-ZnAl-LDO, as well as most LDH-based adsorbents. Further research and density functional theory calculations indicate the differential adsorption enhancement mechanism of the interlayer ions. Chlorine functions as the exchanged anion, whereas fluorine facilitates the complete replacement of chloride ions and hydroxyl groups by phosphate. This finding highlights the potential of utilizing the synergistic effects between different interlayer ions to design and synthesize advanced phosphate adsorbent materials.

Observation of Enhanced Long-Range Ferromagnetic Order in B-Site Ordered Double Perovskite Oxide Cd2CrSbO6.

A B-site ordered double perovskite oxide Cd2CrSbO6 was synthesized under high-pressure and high-temperature conditions. The compound crystallizes to a monoclinic structure with a space group of P21/n. The charge configuration is confirmed to be that of Cd2+/Cr3+/Sb5+. The magnetic Cr3+ ions form a tetrahedral structural frustrated lattice, while a long-range ferromagnetic phase transition is found to occur at TC = 16.5 K arising from the superexchange interaction via the Cr-O-Cd-O-Cr pathway. Electrical transport measurements indicate that Cd2CrSbO6 is an insulator that can be described by the Mott 3D variable range hopping mechanism. First-principles calculations reproduce well the ferromagnetic and insulating ground state of Cd2CrSbO6 with an energy band gap of 1.55 eV. The intrinsic ferromagnetic insulating nature qualifies Cd2CrSbO6 as a promising candidate for possible spintronics applications.

Effect of H2S on the corrosion behavior of austenitic and martensitic steels in supercritical CO2 at 550 °C and 20 MPa for Brayton cycle system

Corrosion of alloy materials significantly influences the stability and efficiency of the supercritical carbon dioxide (S-CO2) Brayton cycle. In this study, we investigated the corrosion behavior of the austenitic alloy SP2215 and the martensitic alloy X19CrMoNbVN11-19 (X19) in S-CO2 at 550°C and 20 MPa. The effect of impurities, H2S, on corrosion behavior was studied. After 900 hours, SP2215 formed a 1.1 μm thick oxide layer (Cr2O3). X19 formed a loose and porous double oxide layer of 4.1 μm (outer: Fe3O4, inner: FeCr2O4). After H2S doping, SP2215 had an oxide layer of 6.2 μm (FeS, SiO2, and Cr2O3), while X19 was 9.8 μm (outer: Fe3O4, SiO2, FexSy and Fe2O3, inner: FeCr2O4, Fe2SiO4 and Cr2S3). Metal sulfides formed and the corrosion layer thickened. This indicates that H2S not only changes the corrosion mechanism but also aggravates the corrosion. However, the corrosion of CO2 is dominant. SP2215 has better corrosion resistance than X19.

Co-sorption of arsenic and fluoride using the hierarchical Mg-La-Fe nanosheets derived from layered double oxides

Considering the prevalent natural occurrence of arsenic and fluoride with a higher concentration gradient in groundwater, in this study, a novel MgLaFe layered double oxide material in the form of highly dispersed curly nanosheets (MLF-NS) was prepared using an urea hydrothermal method and low-temperature hydrogen peroxide exfoliation, applying to purity the contaminants of arsenic and fluoride. The prepared MLF-NS possesses exceptional co-sorption properties for As(III), As(V), and F− and the maximum co-sorption capacities (Qm) of As(III), As(V), and F− reach 36.95 mg g−1, 98.70 mg g−1, and 387.68 mg g−1, respectively, which is superior to those of most similar adsorbents. MLF-NS also exhibits excellent stability and reusability which can effectively regenerate and preserve their high adsorption capacity after four adsorption–desorption cycles. The mechanism investigation reveals the expansion of the interlayers due to the adsorbed arsenic ions, combining with the synergistic effect of motherboard cation coordination and exchanging with anions in the interlayer, plays a crucial role in enhancing the adsorption for both arsenic and fluoride. Meanwhile, the well-dispersed MLF-NS overcome the aggregation disadvantage, and thus exposes more adsorption sites to improve the co-removal efficiency of As(III), As(V), and F−. The collaborative analysis of mean adsorption free energy, FT-IR, AFM, XPS, adsorption energy, and CDD support the findings. Overall, the unique properties of MLF-NS make it a promising solution for effective removal of As(III), As(V), and F− in wastewater treatment.

Narrow Band Gap Base Metal Double Perovskite Oxides Through Copper Doping of Ba2Ca0.66Nb1.33O6

This work examines the influence of copper doping on the structure, optoelectronic properties, and photocatalytic performance of transition metal double perovskite oxides of the Ba2Ca0.67Nb1.33O6 (BCN) family. A solid-state synthesis method was used to achieve partial substitution of Cu2+ in the Nb5+ site (Ba2Ca0.67Nb1.33-xCuxO6-δ, x = 0.05, 0.13, 0.26) and Ca2+ site (Ba2Ca0.67-xCuxNb1.33O6-δ, x = 0.13). The incorporation of copper in BCN resulted in significant changes in the structure and optoelectronic properties. Major differences were observed when Cu atoms occupied the Nb-site versus the Ca-site. The parent compound and Ca-site doped compounds crystallized in a P3 1 space group while Nb-site doped compounds showed increasing Fm3 mixed phase character. Cu doping resulted in a dramatic shift of the absorption band edge towards the visible region. Ca-site doping resulted in a primary band edge shift from 3.8 eV to 2.1. For the Nb-site doped compounds, the primary band-edge remained at 3.8 eV but a secondary band-edge appeared which progressively shifted to smaller energies as Cu doping increased. Ba2Ca0.67Nb1.20Cu0.13O6-δ and Ba2Ca0.67Nb1.07Cu0.26O6-δ exhibited strong absorption of near-infrared photons of wavelength well beyond 800 nm. The double perovskite oxides were utilized as photoanodes for photoelectrochemical water splitting, exhibiting both a visible photoresponse (until wavelengths as low as 520 nm) and good photochemical stability. This work showcases the possibility of forming new low band gap multi-element inorganic semiconductor oxides constituted entirely of base metals and oxygen.

Investigation of the structural, electronic, magnetic, and optical properties of the double perovskite oxide semiconductor La2NiMnO6: Ab initio calculations by using GGA-PBE and GGA + mBJ approximations

In this paper, we examined the La2NiMnO6 double perovskite oxide semiconductor materials, our treatment included the structural, electronic, magnetic, and optical characteristics by utilizing the density functional theory, which was performed in the Wien2k software. The exchange–correlation potential was carried out in combination with the GGA-PBE (Perdew Burke Ernzerhof Generalized Gradient Approximation), and GGA + mBJ (modified Becke and Johnson) was used for the exchange–correlation potentials. The results suggest that the compound La2NiMnO6 exhibits in a ferrimagnetic state. It was also found that the stable ground state of the compound is ferrimagnetic. The results demonstrate that La2NiMnO6 has a band gap whose spin-up value is 0 eV and spin-down (dn) value is 2.86 eV (GGA-PBE), with up values is 0 eV and dn value being of 3 eV (GGA + mBJ). We also explored different optical properties, among them electron energy loss, absorption coefficient, real and imaginary dielectric tensor, and real and imaginary optical conductivity.

An analytical I-V model of SiC double-gate junctionless MOSFETs

Silicon carbide(SiC) double gate junctionless metal oxide semiconductor field-effect transistors(DG JL MOSFETs) have attracted significant attention due to their ideal high temperature characteristics and radiation resistance. Therefore, it is meaningful to exploit an I-V model for SiC DG JL MOSFETs. In this article, we make a linear approximation to describe the relationship between the surface mobile charge density and the surface electron concentration of the device. Based on this approximation and using the one-dimensional Poisson’s equation, we solve for the potential distribution of a SiC DG JL MOSFET in the subthreshold region. From this solution, we derived a functional relationship between the surface mobile charge density in the channel and the channel quasi-Fermi potential. Then we successfully developed a unified I-V model for the SiC DG JL MOSFETs. Based on the drain to source current calculation formula, the calculation expressions for the device’s transconductance and output conductance are derived. By comparing our model with the results from the two-dimensional numerical simulation software Silvaco Atlas, our model’s calculations closely match the two-dimensional numerical simulation results from the subthreshold region to the accumulation region. This model has reference significance for SiC DG JL MOSFETs in the high temperature electronic circuit application field.

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.