Degree Of Inversion Research Articles

Comparing random walks in graph embedding and link prediction.

Random walks find extensive applications across various complex network domains, including embedding generation and link prediction. Despite the widespread utilization of random walks, the precise impact of distinct biases on embedding generation from sequence data and their subsequent effects on link prediction remain elusive. We conduct a comparative analysis of several random walk strategies, including the true self-avoiding random walk and the traditional random walk. We also analyze walks biased towards node degree and those with inverse node degree bias. Diverse adaptations of the node2vec algorithm to induce distinct exploratory behaviors were also investigated. Our empirical findings demonstrate that despite the varied behaviors inherent in these embeddings, only slight performance differences manifest in the context of link prediction. This implies the resilient recovery of network structure, regardless of the specific walk heuristic employed to traverse the network. Consequently, the results suggest that data generated from sequences governed by unknown mechanisms can be successfully reconstructed.

Mechanochemically assisted synthesis, inversion degree and magnetization of spinel compounds across the (Zn,Mg)Fe2O4 system for flexible smart devices

Magnetic spinel oxides are multifunctional materials used or under consideration for a range of applications across electronics, communication technologies, remediation and health. They can also present high magnetostriction coefficients, and are being investigated as active inorganic fillers in polymer matrix composites for flexible sensors and actuators. However, state-of-the-art materials for these later applications are NiFe2O4- and CoFe2O4-based compositions, and it is necessary to find environmentally-friendly alternatives free of toxic elements that provide comparable responses, ideally biocompatible. This work presents a study of the spinel phases across the (Zn,Mg)Fe2O4 system and of their suitability to be used as magnetic component in hybrid composites. Spinel single phase materials with variable particle size across the submicron range, down to the verge of the nanoscale, have been obtained by mechanochemically assisted synthesis for five selected compositions spanning the whole ZnFe2O4-MgFe2O4 system. Evolution of the crystal lattice and inversion degree (amount of Fe3+ at tetrahedral site) has been obtained from Rietveld refinement of synchrotron X-ray diffraction data, and correlated with the development of magnetic ordering. Ferrimagnetic compositions are identified, among which Zn0.25Mg0.75Fe2O4 stands out for its magnetization characteristics comparable to NiFe2O4. This spinel compound is thus a promising environmentally-friendly candidate for flexible devices, in principle also biocompatible.

Niobium doping as a pathway for tuning the optical properties of cobalt ferrites

In this work, the effect of niobium pentachloride concentration (NbCl5) and the influence of the pentavalent niobium ion on the structure and optical properties of cobalt ferrites was studied for the first time. The sol-gel method was applied to synthesize the xerogel with a subsequent heat treatment at 550 °C for 2.5h to obtain the nanoparticle. X-ray diffraction showed the expected spinel phase in all samples. Thus, it was possible to observe a shift in the main reflection (311) and a change in the lattice parameter as the niobium content increased. The crystallite size varied between approximately 18 and 34 nm. The Raman spectra showed typical vibrational modes of cobalt ferrite with no indication of secondary phase modes and variation in the A1g(2) and T2g(1) bands related to the octahedral and tetrahedral sites, respectively. Moreover, there is a correlation to an observed redshift, indicating an increase in the degree of inversion. Diffuse reflectance showed that the band gap of the samples varied from 1.99 eV for the pure sample (Co1.0Fe2.0O4) to 1.6 eV for the highest doping content (Co1.0Nb0.1Fe1.90O4). The coercivity was also affected, ranging from 1253 Oe in the pure sample (Co1.0Fe2.0O4) to 745 Oe in the doped sample (Co1.0Nb0.1Fe1.90O4). These results prove that the optimization of properties was successful since there was a marked decrease in the band gap and an increase in UV absorption. This result shows that it is possible to optimize the optical properties by introducing niobium, an effect that has not been possible in other studies with this type of dopant.

Template synthesis of MgMn2O4 graded porous microspheres and electrochemical properties

Porous materials are more popular in electrochemical applications. In this study, MgMn2O4 microspheres with graded porous structure were prepared at lower temperature using a convenient template method, and MnCO3 microspheres were used as self-sacrificial templates. MgMn2O4 spinel microspheres were also prepared by template free method for comparison. The MgMn2O4 graded porous microspheres obtained by template method were assembled from nanoparticles with size of 20–50 nm, and have larger specific surface area (twice that of MgMn2O4 prepared by template free method). XPS studies show that both materials have mixed spinel structure with Mn present in multivalent states, and the material prepared by template method exhibits lower inversion degree. The electrochemical test results indicate that MgMn2O4 graded porous microspheres prepared by template method exhibit more excellent cycling and rate performance compared to materials prepared by template free method. The initial discharge capacity is up to 1429.5 mAh g−1 at a current density of 100 mA g−1, and discharge capacity remains 778.0 mAh g−1 after 150 cycles. Even at high rates (1000 mA g−1), it can stably output a cycling capacity of 295.5 mAh g−1. The MgMn2O4/LiCoO2 full cell delivers an initial discharge capacity of 83.4 mAh g−1 at a current of 100 mA g−1. The excellent electrochemical performance of MgMn2O4 microspheres prepared by template method may be related to their graded porous structure and low inversion degree. This study indicates that the electrochemical performance of MgMn2O4 materials can be greatly improved by adjusting the microstructural morphology.

Effect of Synthesis Conditions on the Composition, Local Structure and Electrochemical Behavior of (Cr,Fe,Mn,Co,Ni)3O4 Anode Material

AbstractDisordered high entropy spinels (HES) (Cr,Fe,Mn,Co,Ni)3O4 were obtained by solid‐state synthesis and co‐precipitation using various powder precursors. They were characterized by a complex of physico‐chemical methods and investigated as anode materials for lithium‐ion batteries (LIBs). According to XRD and TEM data, the materials are single‐phase. The structural characterization of the samples obtained at 773, 973, and 1273 K was determined using Raman and Mössbauer spectroscopy, and magnetic measurements. The degree of spinel inversion and lattice distortion (microstrains) decrease with increasing synthesis temperature, while the crystallite size increases. The insufficient nickel content in the samples ensures a more uniform distribution of iron cations in both sublattices, which leads to an increase in the lattice parameters and has a positive effect on the de‐/lithiation. Repeated ball‐milling of HES material, prepared by co‐precipitation, increases its specific capacity from 284 mAh g−1 to 492 mAh g−1 at a current density of 100 mA g−1 after 25 cycles. Besides, the smaller crystallite size reduces the volume changes in the materials during de‐/lithiation.

Synthesis of porous Mg2MnO4 spinel microspheres and enhanced lithium storage properties

Porous Mg2MnO4 spinel microspheres were synthesized by a facile solvothermal method. Various techniques such as X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, were used to characterize the phase composition, morphology and electronic structure of materials. The results show that Mg2MnO4 spinel material was obtained at the temperature of 600–800 °C and has a microsphere structure. The microspheres were assembled by nanoparticles, and the particle size increases with the increase of annealing temperature. Analyses of XPS spectra reveal that Mn exists in multiple valence states (+2, +3, +4) in Mg2MnO4 materials, and all the materials are mixed spinel with Mg2+ and Mn2+/3+/4+ ions occupy both tetrahedral and octahedral sites of spinel structure, and the degree of inversion decreases with increasing annealing temperature. Mg2MnO4 microspheres exhibit excellent lithium storage performance, the first discharge specific capacity of M2MO-8 is 835.3 mAh g−1 under a voltage window of 0–3 V and with a current density of 100 mA g−1, and after 100 cycles the discharge capacity of the material is as high as 406.5 mAh g−1. In addition, this material shows high cyclic reversibility. The enhanced lithium storage properties of the material can be attributed to its porous structure, which promote the transport of lithium ions and reduce the damage to the structure caused by the volume change during the charge and discharge process.

Study on the Dispersion Characteristics of Coal Complex Resistivity under the Effect of Liquid Nitrogen Cyclic Freeze-Thaw and Evaluation of Permeability Enhancement.

The effect of liquid nitrogen freeze-thaw fracturing on coal seams can be potentially evaluated by the complex resistivity method. The real part (Reρ) and the imaginary part (Imρ) of the complex resistivity and permeability of coal were determined under different cycle times and in different bedding directions. The reason for permeability enhancement was discussed, and the dispersion mechanism of complex resistivity during cyclic freeze-thaw fracturing was analyzed. The results indicated that (1) the complex resistivity parameters have a good response to the cycle times; Reρ, |Imρ|, and the dispersion degree (α) are positively correlated with cycle time; the fully polarized frequency (f p) of Reρ, the characteristic frequency (f c) of Imρ, and variation are negatively correlated with cycle time. (2) The difference in complex resistivity parameters between the vertical bedding direction and the parallel bedding direction is significant, and the difference in electrical properties of the bedding structure continuously decreases with the increase in cycle time. (3) Under the effect of liquid nitrogen cyclic freeze-thaw, a complex network of fractures in coal is formed, the anisotropic characteristics of coal are weakened, and effective conductive channels are damaged. The peak frost heave force decreases exponentially with the increase in cycle time, and the difference in bedding electrical properties gradually disappears. (4) Comparing the inversion degree of measured data with three conductive models, ρ0 and τ are selected as the optimum parameters for evaluating the effect of liquid nitrogen cyclic freeze-thaw. A logarithmic permeability evaluation model is constructed based on ρ0 and τ. This work provides a new perspective based on electrical detection for evaluating the permeability enhancement of coal during liquid nitrogen cyclic freeze-thaw.

Increase the inversion degree in Er-doped MgGa2O4 spinel nanofilms to obtain strong electroluminescence

The Ga2O3/MgO/Er2O3 nanolaminates are fabricated by atomic layer deposition and crystallized into Er-doped MgGa2O4 spinel (MGS:Er) nanofilms after annealing, with their electroluminescence (EL) performance characterized. The annealing above 600 °C achieves the polycrystalline spinel nanofilm, and the crystallization is promoted by the higher annealing temperature and Ga2O3/MgO ratio. The dopant Er3+ ions preferably substitute into the octahedron sites occupied by Ga3+ ions in ordinary spinel and Mg2+ in anti-spinel lattice, while the inversion degree is confirmed to increase with the reduction of Ga2O3/MgO ratio and annealing temperature, resulting the relatively enhanced secondary EL at 1542 nm. This perturbation by Er3+-substitution into anti-spinel sites improves the emission intensity and excitation efficiencies, the main EL emission peaking at 1531 nm from the optimal MGS:Er device exhibits the excitation efficiency reaching 5.8 %, with the enhanced electrical injection realizing the maximum EL intensity above 17.3 mW/cm2. The fluorescence lifetime of these MGS:Er devices is established in the range of 371–760 μs, which decreases mainly with the Er concentrations. The prototype device using the near-stoichiometric Ga2O3/MgO ratio shows the operation time of 1.12 × 105 s. This work explores the fabrication of Si-based spinel nanofilms with designed composition and special microstructure, and their practical application in optoelectronics.

Ball milling and annealing effect in structural and magnetic properties of copper ferrite by ceramic synthesis

This study aims to better understand the relationship between the microstructure and magnetic properties of copper ferrite, which is an inverse spinel that present a body-centered tetragonal structure associated with a remarkable Jahn–Teller (JT) effect. For this goal, a sample has been synthesized by the ceramic route from a stoichiometric mixture of high-purity CuO and Fe2O3 powders activated mechanically in a high-energy planetary ball mill. This sample was calcined in air furnace at 1000 ºC for 6 h. As synthetized sample with a cubic structure was divided into two parts and one of them was annealed at 650 ºC for 3 h and slowly cooled to room temperature to obtain a pure tetragonal spinel sample. Furthermore, these two samples were subjected to the same processes of severe plastic deformation by milling for up to 70 h and subsequent annealing at temperatures ranging between 300 and 600 ºC to obtain samples with a mixture of phases in different proportions. For the cubic one, there is no change in its structure due to milling, always remaining 100 % cubic, and the evolution in the saturation magnetization was related to the changes in the density of defects present. On the other hand, copper cations are always found in the octahedral sites of spinel with a tetragonal structure. The small decrease in the degree of inversion to 0.95 induced by milling in this sample is capable of breaking the JT distortion, giving rise to the appearance of a cubic phase. This work demonstrates how the structure, microstructure, defects like stacking faults and deformation twins, and degree of inversion of the different phases are related to changes in magnetic properties.

High-efficient separation of photoinduced charge carriers in CoFe2O4-ZnO magnetic heterostructures mediated by oxygen vacancies

In this work, magnetic heterostructures were obtained by the in-situ growth of various ZnO amounts on the preformed CoFe2O4 nanoparticles. The X-ray diffraction characterization shows the presence of both ZnO and CoFe2O4 crystalline phases, and the crystallite size is about 13–14 nm for both components. X-Ray Photoelectron Spectroscopy (XPS) analysis revealed a CoFe2O4 inversion degree of 0.7. The composite samples demonstrated an extended absorption edge into the visible range. The sample’s magnetic properties were investigated by vibrating-sample magnetometer (VSM) and correlated with Electron Paramagnetic Resonance (EPR) results. The magnetic behavior was attributed to the combination of CoFe2O4 and ferromagnetic ZnO. The emergence of a ferromagnetic phase within ZnO was elucidated to originate from charge/spin transfer of spin-up polarized states from the CoFe2O4 Fermi level into empty oxygen vacancies of ZnO. High efficiency in Rhodamine B (RhB) degradation under visible light was observed in the prepared composite materials, particularly with an optimal CoFe2O4-ZnO ratio of 1:5, achieving an 81 % degradation rate within 6 h. The proposed photodegradation mechanism, based on various spectroscopic and magnetic investigations, highlights the role of spin transfer and oxygen vacancies in facilitating reactive oxygen species (ROS) generation for pollutant degradation.

Rietveld analysis and cation distribution of Co substituted Ni–Zn ferrite nanoparticles

This study investigates the cation distribution in Co-substituted Ni–Zn ferrite nanoparticles synthesized via the sol-gel auto-combustion method. The research aims to understand the modifications in cationic distributions at the nanoscale compared to bulk counterparts and their impact on electromagnetic properties. Rietveld structural analysis, lattice constant determination, and magnetic moment measurements were employed to analyze the nanoparticles. The results reveal a single-phase spinel structure with cubic symmetry, crystallite sizes between 26.2 and 36.4 nm, and saturation magnetizations ranging from 50 to 68 emu/g. Results and calculated cation distributions of these ferrite nanoparticles were evaluated in terms of compositional modifications, particle sizes, and related inversion degree parameters. The study confirms the cation distributions based on X-ray and magnetic data, highlighting the importance of cationic inversions in designing nanoscale ferrites with improved electromagnetic characteristics for electronic applications.

Nickel-Catalyzed Cyanation of Allylic Alcohols: High Degree of Chiral Inversion in Aqueous Reaction Media.

Nickel-catalyzed aqueous cyanation of allylic alcohols is herein described. This catalytic protocol provided environmentally friendly and operationally simple access to a variety of allylic nitriles in good yields. For chiral allylic alcohols, the reaction gave chiral allylic nitriles with a high degree of chiral inversion. The accelerated release of cyanide in H2O was crucial for the success of this reaction.

Understanding the impact of support materials on CoFe2O4 catalyst performance for hydrogen fuel and nanocarbon production via methane decomposition

This study focuses on assessing the performance and durability of three distinct catalysts, namely CoFe2O4/MgO and CoFe2O4/TiO2 and CoFe2O4/Al2O3 in the methane decomposition process. These catalysts were synthesized using a co-precipitation impregnation route. Their catalytic activity of methane decomposition was examined in a fixed-bed reactor at a temperature of 800 °C under atmospheric pressure. Various appropriate analytical techniques were employed to explore the physicochemical characteristics of both the fresh and spent catalysts. The SEM images, XRD and H2-TPR results of fresh catalysts revealed strong dependence on the support type. The XPS results confirm the presence CoFe2O4 species on the surface of supports. The CoFe2O4/MgO catalyst has a higher inversion degree compared with other catalysts as confirmed from Raman results. The methane conversions at the end of the reaction time (300 min) were found to be 66 %, 34 % and 2.48 %, while the rates of hydrogen formation corresponding to these methane conversions are 134.73 × 10−5, 68.25 × 10−5 and 8.80 × 10−5 mol H2 g−1 min−1 for CoFe2O4/MgO and CoFe2O4/TiO2 and CoFe2O4/Al2O3 catalysts, respectively. SEM images verified the existence of filamentous carbon on the surface of the spent CoFe2O4/MgO catalyst, whereas the spent CoFe2O4/TiO2 catalyst showed a mix of carbon chunks and filaments and fluffy carbon over the CoFe2O4/Al2O3 catalyst. Ultimately, the quantity of deposited carbon was significantly associated with catalytic activity, as they were 56, 46 and 4 wt% for the spent CoFe2O4/MgO, CoFe2O4/TiO2 and CoFe2O4/Al2O3 catalysts, respectively.

Enhancement the electrical and linear/nonlinear optical properties of ZnCo2O4 through Al3+doping

In this work, ZnCo2O4 samples doped with Al3+ were prepared by the hydrothermal method. Synchrotron x-ray diffraction, FTIR, SEM and EDX techniques were used to investigate the structure, microstructure, morphology, and composition of ZnCo2-xAlxO4 samples. Rietveld analysis revealed a nearly inverse structure for the undoped ZnCo2O4. The degree of inversion is increased upon increasing the Al3+ doping content. Al ions preferentially occupy the octahedral B-site. The optical band gaps of ZnCo2−xAlxO4 samples are 1.9, 1.8 and 1.91 eV for x = 0, 0.1 and 0.2, respectively. Different empirical models were used to obtain the refractive index of the different samples using their corresponding optical band gaps. The increase in non-linear optical values in the sample with x = 0.1 suggested that this sample could be used in a variety of photonic applications. The effects of frequency and temperature on the dielectric permittivity, impedance and electrical modulus of different samples were explored. All samples exhibited the non-Debye relaxation phenomenon. The relaxation time of each sample is affected with the frequency and temperature. The Cole-Cole curve is employed to reduce uncertainty regarding the electrical characteristics of these ZnCo2−xAlxO4 samples induced by grain boundaries or bulk grain. The substitution of Al3+ ions can regulate the conductivity of the ZnCo2O4 sample.

Magneto-induced topological phase transition in inverted InAs/GaSb bilayers

We report a magneto-induced topological phase transition in inverted InAs/GaSb bilayers from a quantum spin Hall insulator to a normal insulator. We utilize a dual-gated Corbino device in which the degree of band inversion, or equivalently the electron and hole densities, can be continuously tuned. We observe a topological phase transition around the magnetic field where a band crossing occurs, accompanied by a bulk-gap closure characterized by a bulk conductance peak (BCP). In another set of experiments, we study the transition under a tilted magnetic field (tilt angle ). We observe the characteristic magnetoconductance around BCP as a function of , which dramatically depends on the density of the bilayers. In a relatively deep inversion (hence a higher density) regime, where the electron-hole hybridization dominates the excitonic interaction, the BCP grows with . On the contrary, in a shallowly inverted (a lower density) regime, where the excitonic interaction dominates the hybridization, the BCP is suppressed indicating a smooth crossover without a gap closure. This suggests the existence of a low-density, correlated insulator with spontaneous symmetry breaking near the critical point. Our highly controllable electron-hole system offers an ideal platform to study interacting topological states as proposed by recent theories. Published by the American Physical Society 2024

Optimizing the synthesis of ZnFe2O4 through chemical and physical methods: effects of the synthesis route on the phase purity, inversion, and magnetic properties of spinel zinc ferrite

In this work, ZnFe2O4 ferrites were prepared by chemical (coprecipitation) and ceramic (ball-milling) methods. The effects of the synthesis route on the phase purity, crystallinity, particle size distribution, and magnetic properties were investigated to identify the most appropriate conditions for the synthesis of high-quality ferrites. The samples were examined by x-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and Mössbauer spectroscopy. The XRD patterns revealed that a high-purity spinel phase was obtained by coprecipitation at pH ≥ 7 by calcining the pristine powder at T ≥ 900 °C, whereas a single spinel phase was obtained at T ≥ 700 °C in the ball-milling method. The crystallite size of the spinel phase exhibited general increasing trends with the increase of the pH value under the same heat-treatment conditions and with the increase of the calcination temperature. Additionally, the mean physical particle size exhibited an increasing trend with the increase of the calcination temperature. The VSM measurements revealed a noticeable degree of inversion in the spinel ferrites prepared by coprecipitation (exhibiting the highest degree at pH = 10) and an insignificant degree of inversion in the spinel ferrites prepared by the ceramic method. However, calcining the powder exhibiting the highest degree of inversion (prepared by coprecipitation at pH = 10) at 1100 °C resulted in ordering the zinc ions at tetrahedral sites of the spinel structure. Mössbauer spectra for representative zinc ferrite samples prepared by the two methods revealed a major central doublet (with a small magnetic sextet corresponding to the α-Fe2O3 phase in the sample at pH = 7). The hyperfine parameters of the doublet observed in the Mössbauer spectra of the samples, and the corresponding magnetization behavior revealed a higher degree of ionic disorder in the spinel ferrite prepared by coprecipitation.

Hyperspectral estimation model of soil organic matter content based on principal gradient grey information

PurposeIn order to explore a new estimation approach of hyperspectral estimation, this paper aims to establish a hyperspectral estimation model of soil organic matter content with the principal gradient grey information based on the grey information theory.Design/methodology/approachFirstly, the estimation factors are selected by transforming the spectral data. The eigenvalue matrix of the modelling samples is converted into grey information matrix by using the method of increasing information and taking large, and the principal gradient grey information of modelling samples is calculated by using the method of pro-information interpolation and straight-line interpolation, respectively, and the hyperspectral estimation model of soil organic matter content is established. Then, the positive and inverse grey relational degree are used to identify the principal gradient information quantity of the test samples corresponding to the known patterns, and the cubic polynomial method is used to optimize the principal gradient information quantity for improving estimation accuracy. Finally, the established model is used to estimate the soil organic matter content of Zhangqiu and Jiyang District of Jinan City, Shandong Province.FindingsThe results show that the model has the higher estimation accuracy, among the average relative error of 23 test samples is 5.7524%, and the determination coefficient is 0.9002. Compared with the commonly used methods such as multiple linear regression, support vector machine and BP neural network, the hyperspectral estimation accuracy of soil organic matter content is significantly improved. The application example shows that the estimation model proposed in this paper is feasible and effective.Practical implicationsThe estimation model in this paper not only fully excavates and utilizes the internal grey information of known samples with “insufficient and incomplete information”, but also effectively overcomes the randomness and grey uncertainty in the spectral estimation. The research results not only enrich the grey system theory and methods, but also provide a new approach for hyperspectral estimation of soil properties such as soil organic matter content, water content and so on.Originality/valueThe paper succeeds in realizing both a new hyperspectral estimation model of soil organic matter content based on the principal gradient grey information and effectively dealing with the randomness and grey uncertainty in spectral estimation.

Mechanistic insight and first principle analysis of cation-inverted zinc ferrite nanostructure: A paradigm for ppb-level room temperature NOx sensor

Herein, we adopted a new paradigm for developing a high-performance gas sensor by leveraging the mixed spinel ZnFe2O4 structure (mZFO) to enhance the adsorption of NOx molecules. Material characterization reveals the formation of the mZFO due to the cation inversion in lattice sites. The estimated value of the inversion degree is observed to shift from 0.78 to 0.39 with an increase in the calcination temperature. The mZFO nanoparticles calcined at 500 °C show exceptional sensing performance due to their suitable grain size (∼2 times Debye length), neck diameter, and surface area. The sensing studies conducted at various NOx concentrations indicate that the sensor can detect ppb level of NOx with a detection limit of about 9 ppb at room temperature. The detailed sensing mechanism is elucidated based on the density functional theory calculations (DFT) and Bader charge analysis. The outstanding sensor performance is attributed to the formation of a mixed spinel structure, wherein the adsorption energy of NOx (∼-0.6 eV) in the presence of surface adsorbed oxygen is higher than that of the normal spinel structure (∼-0.1 eV). Furthermore, the sensor exhibited a fast response and recovery times (7 and 92 s at 800 ppb NO2), excellent stability, and selectivity. The practical suitability of the mZFO sensor was studied by analyzing the vehicle exhaust emissions. We strongly believe this work would pave a novel approach to developing a high-potential gas sensor by modifying the cation distributions in the spinel ferrites.

Tuning benzene activity of cobalt-based spinel catalysts with cation substitution

Cobalt-based spinel oxides are promising low-cost catalysts for volatile organic compounds (VOCs) elimination. Herein, we prepared the cobalt-based spinel oxides (MCo2O4: M = Ni, Cu, Co, Zn) by a one-step solvothermal method to evaluate the influence of cation substitution on benzene combustion. The cation distribution on tetrahedral and octahedral sites could influence the degree of inversion in cobalt-based spinel oxides, thus achieving the regulation of Co-O bond strength. NiCo2O4 catalyst with the inverse spinel structure had the weak Co-O bond strength, which is conducive to the activation of lattice oxygen to improve the activity of benzene degradation. This work provides deep insights into the influence of the cation substitution on the cobalt-based spinel catalysts for the efficient benzene oxidation.

The impact of tectonic inversion on diagenesis and reservoir quality of the Oligocene fluvial sandstones: The upper Huagang formation, Xihu Depression, East China Sea Shelf Basin

Inversion tectonics are of paramount importance for forming a range of hydrocarbon traps and reservoirs for petroleum exploration. Also, the uplift and exhumation of strata, the activation and creation of faults and leakage or breaching of hydrocarbon traps are often attributed to multiple inversion. Changes in fluid activity and the geochemical system are frequently observed during such tectonic inversions. However, the impacts of tectonic inversion on fluid flow and potential diagenetic alterations within deeply buried sandstone reservoirs are not fully understood, posing challenges to accurately assessing reservoir quality and furthering exploration efforts. The Oligocene fluvial sandstones in the Yuquan anticline of the Xihu Depression were investigated by XRD, optical microscope and SEM-EDS-CL along with and petrophysical data to illustrate the impact of tectonic inversion on the evolution of diagenesis and reservoir quality. The two representative exploration wells, C-1 and C-2, originating from the same provenance and sedimentary background in Yuquan anticline, exhibit significant diagenetic alterations attributed to varying degrees of tectonic inversion. Notably, well C-1 has experienced more intense alterations and dissolution of detrital grains compared to well C-2 (average secondary pore, well C-1: 4.8%, well C-2: 2.9%), particularly the complete dissolution of plagioclase grains. Moreover, the content of authigenic kaolinite and quartz cement of well C-1 is higher than that of well C-2, averaging 7.2%, 4.5% and 5%, 1.7% respectively. This diagenetic difference is attributed to the fact that the activity of early NE-NNE oriented faults and the development of late nearly E-W oriented faults are stronger in the northern well C-1 field than in the central well C-2 field. The structural characteristics resulting from tectonic inversion led to enhanced efficiency in both organic acid supply from underlying source rocks in well C-1 field and export of dissolution products within the diagenetic system when compared with Well C-2 field. Regional tectonic inversion plays a predominant role in improving reservoir quality than sedimentary factors in the study area. While the well C-1 has a higher porosity than well C-1 (well C-1: average 18%, well C-2: average 13.1%), the permeability of well C-1 is worse than that of well C-2, with an average of 14.7 mD and 27.9 mD respectively. The alteration and dissolution associated with tectonic inversion significantly enhance the porosity of sandstone reservoirs. However, the formation of secondary pores and dissolution products can complicate the pore system of reservoirs, thereby reducing the reservoir permeability. Our research aims to provide a better understanding of fluid-rock interactions and genetic mechanisms in gas-bearing sandstone reservoirs under varying degrees of tectonic inversion. This will support pre-drill evaluations of reservoir quality in deeply buried formations as well as other analogous targets.