Vacancy Transfer Research Articles

A Study on Oxygen Vacancy Resistance Mechanism of V2O5

Introduction: Due to its magnetic and semiconductor properties, V2O5 has shown tremendous potential in resistive switching memory. Method: Therefore, this paper investigates the resistive mechanism of oxygen vacancies in V2O5. The formation energies of different oxygen vacancies are calculated. Results: The results indicate that oxygen vacancies tend to form single-component conductive filaments. In mixed oxygen vacancies clusters, the charge transfer characteristics and density of states of the V2O5-VO 13 vacancies are the most significant, which is consistent with the analysis of formation energy data. Conclusions: Additionally, the charge transfer of cluster oxygen vacancies was calculated, showing that V atoms directly connected to oxygen vacancies tend to lose electrons, while adjacent oxygen atoms are more likely to gain electrons. In V2O5-VO 12 and V2O5-VO 13, the number of electrons obtained by O2 and O16 exceeds the average by 36.4% and 33.2%. Thus, the formation of oxygen vacancies effectively improves the resistance characteristics of the V2O5.

Vacancy transfer probability parameters: Database and a new empirical value for elements in the atomic number range 16 ≤ Z ≤ 92

In the present work, we offer a collection of documented values for vacancy transfer probabilities (ηXY, X=K,Li;Y=L,M,N,Li,Mj,Np,Op;i=1,2,3;j=1,2,3,4,5;p=1,4,5) sourced from published technical literature spanning 1993 to 2023 for elements in the atomic range 16≤Z≤92. We found 1200 experimental vacancy transfer probability values from 68 scientific papers, during the specified period. These have been compiled and summarized in tables, encompassing various parameters and elements. This data is also comprehensively analysed, including tables that display weighted average vacancy transfer probability (ηXY)W values along with the combined standard deviation and the average z-score. We also recommend a new collection of empirical values for the atomic parameters ηKL(T),ηKL2(R),ηKL3(R),andηKM(R) of vacancy transfer probabilities. This compilation offers an overview of the present state of atomic data for vacancy transfer probabilities. It is a valuable resource to guide future experimental and theoretical studies in this area.

Hetero-Interface Engineering on 9.0wt% CoOx-Doped CeO2 Nanorods as Electromagnetic Wave Absorber and Integrated into Multifunctional Aerogel.

Ceria (CeO2) becomes a promising candidate as electromagnetic wave absorbing materials (EWAMs) for their abundant natural source, rich oxygen vacancy, charge conversion, and electron transfer abilities. However, it remains challenging to regulate its nanoscale and atom-scale composition to optimize the absorbing performance and develop high-performance commercial devices. Herein, a facile method to large-scale synthesis CeO2@Co-x% (x = 5, 7, 9, 11, 13) series EWAMs with diverse amounts of decorated CoOx is presented. By modulating the ratio of doped CoOx, a rational hetero-interface is created in CeO2@Co-9% to enhance natural and exchange resonances, improving magnetic loss capability and optimizing impedance matching. Doped CoOx promotes the charge accumulation, interfacial polarization, and multiple scattering of the CeO2 for strengthening the EW absorption and attenuation, which display superb minimum reflective loss (RLmin) of -74.4dB with a wide effective absorbing bandwidth (EAB) of 5.26GHz. Furthermore, a dual crosslinking strategy is employed to fabricate CeO2@Co-9% into an aerogel device with integrated lightweight, heat insulation, compression resistance, and fame-retardant functions. This work presents an excellent example of large-scale fast synthesis of high-performance CeO2-based EWAMs and multiplication 3D devices.

Mechanistic aspects of the reduction of rutile titanium dioxide and its Re-oxidation. Development and destruction of crystallographic shear structures

A model is presented giving the mean dimensions of acicular octadecahedral microcrystallites of a rutile titanium dioxide powder. Reduction at 823 K, in conjunction with ESR, electrical conductivity and controlled re-oxidation has enabled the model to be applied to reduced microcrystallites. At 300 K they contain <0.1% of paramagnetic [Ti3+↑ VO:↑Ti3+] reduced edge sites and >99.9% of reduced spin-paired [Ti3+↑↓ Ti3+ VO:] sites. These sites are situated on the external crystal faces and on polygonal bulk crystallographic shear (CS) structures inclined to the microcrystal four-fold symmetry axis. CS structures are quantum-sized [Ti4O7VO:] environments which broaden the paramagnetic signals at 78 K. Temperature programmed reduction in H2(g) reveals atomic hydrogen as a precursor to CS structure formation via a lattice template formed on microcrystallite faces. Shear structures are oxidised on their polygonal perimeters at differing rates on the respective microcrystallite faces by anionic vacancy transfer from sub-surface regions.

Kβ to Kα X-ray intensity ratio and K–L vacancy transfer probability of Mn following electron capture decay

Kα and Kβ X-rays of Mn following electron capture (EC) decay of 55Fe were detected using Amptek XR-100 T-CdTe X-ray detector spectrometer. Measured Kα and Kβ X-ray intensities of Mn were used to determine the Kβ to Kα intensity ratio and total K–L total vacancy transfer probability. These values were compared with the theoretical, semiempirical, and others’ experimental values obtained via EC decay as well as photoionization. The X-ray intensity ratio of Mn was found to be higher by 1.5% from the relativistic Hartree-Slater theoretical value. This deviation may be attributed to the exchange interactions occurring between the 3p and 3d shell electrons as well as the recoil effect of the nucleus due to neutrino emission.

EVOLUTION OF THE DEFECT STRUCTURE OF Pd–11.3 at. % W ALLOY DURING RELAXATION AT MULTIPLE HYDROGENATION

The influence of the hydrogen and vacancies introduced into an alloy matrix as a result of electrolytic hydrogenation on the structural state of Pd–11.3 at % W alloy after fourfold hydrogenation has been studied. It is established that nonmonotonic changes in the sample defect structure are determined by the transformation of single vacancies into vacancy complexes (micropores and small dislocation loops), their decay during relaxation, and migration of vacancies from the matrix to the boundaries of coherent-scattering regions (CSRs) and backwards. The vacancy transformation rate into defect complexes depends on their concentration. Long-term relaxation of the alloy leads to almost complete transfer of vacancies from the matrix to the CSR boundaries. An interpretation of the obtained experimental data within the theory of development of hierarchical defect structures is proposed.

First-principles study on silicon emission from interface into oxide during silicon thermal oxidation

Using the first-principles calculation, the diffusion path is explored in the Si emission from the interface into the Si oxide surface during the Si oxidation process, by assuming that the Si emission dominantly consists of a SiO interstitial diffusion. Searching for the diffusion path was succeeded and the energy profile of diffusion path can be evaluated. At this time, only three elementary processes, such as O vacancy transfer, coordination number conversion of Si, and ACBD bond order conversion, were just considered. It has been confirmed that the SiO interstitial moves in the oxide with sequentially kicking the neighboring Si and O like a billiards, and that the kicked-out Si and O become a new SiO interstitial, while Si and O belonging to the old SiO interstitial are absorbed as a part of the oxide. Furthermore, the energy profile of similar diffusion path in bulk SiO2 crystal is also compared. It is revealed that the Si oxide layer is relatively flexible against structural deformation, and that the oxide surface is much more flexible, but that the oxide layer near the interface is less flexible due to the influence of the rather rigid Si substrate. The results indicate that our assumption on the Si emission in the Si oxidation process is fair, and that the SiO interstitial diffusion in the oxide film is inevitable in order to reduce the impact of volume expansion that occurs at the interface.

K shell fluorescence parameters of some elements at 59.54 keV: Experimental and theoretical results

Kα, Kβ and total K X-ray fluorescence cross-sections, K shell fluorescence yields, Kβ/Kα X-ray intensity ratios, K shell level widths, K shell life times, K to L shell vacancy transfer probabilities, K shell jump ratios, Auger electrons emission ratios and excitation factors for some elements in the atomic number range 22 ≤ Z ≤ 48 have been investigated. A Si(Li) detector and Am-241 annular radioactive source were used in the measurements. The obtained experimental data were crosschecked with theoretically calculated results and other available experimental results from the literature. It was observed that there is a good agreement between them within experimental uncertainties.

Inner-shell ionisation of Xe[formula omitted]–Au and Pb collision systems: MO picture

The generation of collision-induced vacancies and their transfer within the electronic inner shells are the source of several unprecedented phenomena, which have been revealed in recent experimental studies conducted using state-of-the-art next-generation accelerators and detectors. Despite the multitude of studies conducted over the years, our understanding of the atomic vacancy transfer mechanisms remains exiguous. The detection and analysis of collision-induced X-rays is a widely-used powerful technique for analysing atomic-scale phenomena. However, both experimental and theoretical investigations on ion–atom collision-induced X-rays have remained mostly restricted to high-energy light-ion impact on heavy atoms. To date, only a few studies have been reported on the investigation of very-low-energy heavy-ion impact on heavy atoms using X-rays, especially M-shell X-rays of the heavy atom. This study was conducted to evaluate the inner-shell ionisation of Au (135 and 508 μg/cm2) and Pb (107, 157 and 390 μg/cm2) targets due to low-energy (2–5 MeV) 54Xeq+-ion impact. The collision-induced X-ray spectra of both the collision partners were examined, and the corresponding intensity ratios and cross-sections were compared with those calculated using two well-known ionisation theories, viz. PWBA and ECPSSR. The measured cross-sections were underestimated by these theories. Moreover, the cross-sections measured in this study were found to be several orders of magnitude higher than those obtained in other reported studies on low-energy lighter-ion-impact on Au and Pb. The significant discrepancies observed between the experimental and theoretical values have been explained qualitatively within the framework of quasi-molecular orbital formation using level correlations. The insights obtained from the results of this study can be applied to analyse the vacancy transfer mechanisms in very-heavy systems (combined atomic number > 100).

β particles induced directional inward migration of oxygen vacancies: Surface oxygen vacancies and interface oxygen vacancies synergistically activate PMS

In this work, a high-energy β electron beam was applied to promote the generation and directional inward migration of surface oxygen defects. The valence band potential changed to a high potential due to the transfer of surface oxygen vacancies on BiVO4/Bi2O3−x. Interface oxygen vacancies have significant advantages in inducing the formation of oxygen vacancy levels and reducing the band gap energy. Surface oxygen vacancy and vacancy levels can prevent the recombination of photogenerated carriers. The electrons enriched in the surface oxygen vacancies can remarkably activate PMS with O−O bonds to degrade ciprofloxacin (CIP). The degradation kinetic constant and CIP mineralization rate of BiVO4/Bi2O3−x-450/PMS were 2.09 and 1.51 times higher than those of BiVO4/Bi2O3−x/PMS, respectively. BiVO4/Bi2O3−x-450 with a lower relative content of surface oxygen vacancies (24.70%) exhibited a stronger activation ability. Obviously, the change of band structure caused by interface oxygen vacancies is the reason for increasing photoactivation efficiency of PMS.

Mathematical modeling of memristor resistive switching based on mass transfer full model of oxygen vacancies and ions

A relatively simple mathematical model of dynamic switching of a memristor has been created based on a fairly complete physical model of the processes of stationary mass transfer of oxygen vacancies and ions, considering their generation, recombination and diffusion in electric field in the “metal-oxide-metal” structure with the dominant transport mechanism of electron tunneling through oxygen vacancies. The results of numerical simulation of mass transfer of oxygen vacancies along thickness of the oxide layer of the memristor are presented. The distributions of vacancy concentration during their diffusion in an electric field are found, taking into account the processes of generation and recombination with ions, depending on the applied voltage to the electrodes and on the temperature of the memristor. A good coincidence of the volt-ampere characteristics part found as a result of numerical simulation and a series of experiments is obtained. It is shown that under conditions of more than 600 K memristor temperature, it is possible to neglect the process of ion-vacancy recombination and significantly simplify the procedure for mathematical modeling of memristor resistive switching by eliminating the oxygen mass transfer equation, as well as the recombination term in the stationary equation of oxygen vacancies mass transfer. The developed mathematical model of memristor dynamic switching, including a system of stationary ordinary differential equations, is designed to simulate the operation of large memristor arrays in neuromorphic computing devices and may be preferable in relation to known circuit models that include a certain set of fitting parameters to match the simulation results with the memristor experimental characteristics.

Conductivities and transport properties of Ca(Zr/Hf)0.9Sc0.1O2.95

Doped CaZrO3 proton conductors are promising materials for electrochemical hydrogen sensors, which have already been used in commercialized hydrogen sensors for aluminum melts. Hafnium and Zirconium possess similar properties but their influences on conductive properties of CaZrO3 proton conductors have not been well investigated. In this study, CaZr0.9Sc0.1O2.95 and CaHf0.9Sc0.1O2.95 were prepared by solid-state reaction, and their conductivities and transport properties were systematically investigated by defect equilibria model. Total conductivities of CaZr0.9Sc0.1O2.95 and CaHf0.9Sc0.1O2.95 reached 4.70 × 10−5−1.69 × 10−3 S·cm−1 and 4.83 × 10−6−9.71 × 10−4 S·cm−1 under humid air and 400 °C−800 °C. Their total standard molar hydration enthalpies were estimated to −59.1 kJ/mol and −56.9 kJ/mol, respectively. Conductivities of grain interiors were higher than those of total conductivities, and activation energies of protons were lower than oxide vacancies and holes. Transport numbers showed protonic conduction of Ca(Zr/Hf)0.9Sc0.1O2.95 to always dominate under humid air at 400 °C−700 °C. Protonic transport numbers of CaZr0.9Sc0.1O2.95 and CaHf0.9Sc0.1O2.95 were estimated to 0.41 and 0.44 at 800 °C, respectively. Meanwhile, protonic transport number of grain interiors was higher than that of total sample. Therefore, grain interior could block the transfer of oxide vacancies and holes. In sum, these findings look promising for application on electrochemical hydrogen sensors.

Green emission in Fe- and Mn-doped ZnO nanowires studied by magneto-photoluminescence

The green emission in ZnO, which was reported to result from deep-level transitions and proportional to the concentration of singly ionized oxygen vacancy, is critical for the visible-band optoelectronic application. However, the effective modulation of the green emission intensity is challenging. In this study, the green emission in ZnO nanowires is greatly suppressed by Fe doping and enhanced by Mn-doping during the growth process. Temperature dependent PL spectra demonstrate strong electron-phonon coupling, while magneto-PL show shrinkage of electron wavefunction for ZnO:Fe, these indicate both the electron-dopant energy transfer and decrease of oxygen vacancies in ZnO:Fe suppress the green emission; whereas for ZnO:Mn, its PL spectra show weak temperature and magnetic field dependence, which signify very high concentration of the oxygen vacancies that enhance the green emission.

Production of secondary electrons and photons and energy absorption mechanisms in amorphous carbon irradiated by photons in the energy range of 0.03 to 17.4 keV

Energy absorption mechanisms in amorphous carbon under irradiation by 0.03–17.4 keV photons is studied by Monte Carlo simulation with accounting for the cascade decays of inner-shell vacancies and tracking all secondary electrons and photons including very-low-energy ones. Energy absorption by the atoms of the sample that underwent initial ionization by incident photons is only important at energies of several tens of eV (UV and XUV range). The principal mechanism of energy absorption on the whole incident photon energy interval is through inelastic processes caused by secondary electrons. At incident photon energies above C1s ionization threshold low-energy KLL Auger electrons produced by the cascade decay of C1s vacancy transfer energy to the medium in the vicinity of the site of initial photoionization. At energies far above the C1s-threshold, high-energy photoelectrons spread the absorbed energy over larger volumes and with smaller density. A great portion of the energy brought by incident photons, about 42 %, is transferred to the medium by low-energy secondary electrons and photons that are incapable of ionizing or exciting the atoms of the sample. The number of low-energy electrons is proportional to the energy of an incident photon, and at incident photon energies of several keV, one initial photoionization produces hundreds of secondary low-energy electrons.

Promoting electron transfer of surface oxygen vacancies in Pd/CeO2-RE via doping engineering for enhancing catalytic activity in Suzuki coupling reaction

Doping engineering is considered as a facile and effective method for improving the physical and chemical properties of CeO2. Herein, rare earth (RE) ions (La and Nd) doped Pd/CeO2 with the coaxial double-nanotube structure were manufactured by the electrospinning and high-temperature calcination. Through the doping engineering, the original morphologies of Pd/CeO2 were not destroyed and all the elements were uniformly distributed on the surface of nanotubes. XRD, Raman and UV–vis characterizations revealed that La3+ and Nd3+ ions were incorporated into the CeO2 lattice, while the cubic fluorite structure of CeO2 was maintained. Moreover, it has been proved that there were oxygen vacancies existed on the surface of CeO2 and the concentration of oxygen vacancies increased significantly as the radius of RE ions increases. In addition, an electron transfer pathway between CeO2 and Pd nanoparticles was proposed based on the experimental data and Density Functional Theory (DFT) calculations. The Pd/CeO2-La catalyst with abundant oxygen vacancies showed a high catalytic performance for Suzuki coupling reaction under mild conditions without any phase-transfer reagent, toxic solvent and inert protective atmosphere, which realizing the green catalysis.

Determination of L-shell fluorescence parameters of thallium in thallium compounds

The Li (i = l, α, β, and γ) production cross-sections, L-shell average fluorescence yields, and Coster-Kronig vacancy transfer factors for L3 subshell X-rays of thallium in some thallium compounds were determined using Energy Dispersive X-ray Fluorescence spectrometer. The compounds were excited by 59.5 keV gamma-rays from an Americium-241 annular radioactive source, and the L X-rays emitted by the compounds were counted using an ultra-low energy germanium detector with a resolution of 150 eV at 5.9 keV. The production cross-sections, average fluorescence yields, and Coster-Kronig vacancy transfer factors of thallium in these compounds were compared with theoretical calculations and available experimental values of the pure thallium.

Switching between Proton Vacancy and Excess Proton Transfer Pathways in the Reaction between 7-Hydroxyquinoline and Formate.

Bifunctional or amphoteric photoacids simultaneously present donor (acidic) and acceptor (basic) properties making them useful tools to analyze proton transfer reactions. In protic solvents, the proton exchange between the acid and the base is controlled by the acidity or basicity strength and typically occurs on two different pathways known as protolysis and hydrolysis. We report here how the addition of a formate base will alter the relative importance of the possible reaction pathways of the bifunctional photoacid 7-hydroxyquinoline (7HQ), which has been recently understood to predominantly involve a hydroxide/methoxide transport mechanism between the basic proton-accepting quinoline nitrogen site toward the proton-donating OH group with a time constant of 360 ps in deuterated methanol (CD3OD). We follow the reaction dynamics by probing the IR-active marker modes of the different charged forms of photoexcited 7HQ, and of formic acid (HCOOD) in CD3OD solution. A comparison of the transient IR spectra as a function of formate concentration, and classical molecular dynamics simulations enables us to identify distinct contributions of “tight” (meaning “contact”) and “loose” (i.e., “solvent-separated”) 7HQ–formate reaction pairs in our data. Our results suggest that depending on the orientation of the OH group with respect to the quinoline aromatic ring system, the presence of the formate molecule in a proton relay pathway facilitates a net proton transfer from the proton-donating OH group of 7HQ-N* via the methanol/formate bridge toward the quinoline N site.

Spindle-shaped CeO2/biochar carbon with oxygen-vacancy as an effective and highly durable electrocatalyst for oxygen reduction reaction

Highly durable and active CeO2 on biochar carbon (CeO2/BC) derived from Spirulina platensis microalgae and synthesized by simple one-pot hydrothermal treatment and further activated through pyrolysis approach. A spindle-shaped morphology of CeO2 with predominant (111) facet was evidently observed from X-ray diffraction patterns and electron microscopy images. The structural features such as high specific surface area, defect-rich carbon with N & P atoms, increased oxygen vacancy and π-electron transfer play an important role for the improved oxygen reduction reaction (ORR). The considerable amount of Ce3+ and higher proportion of pyridinic N and graphitic N species are substantially contributed to the superior ORR performance of CeO2/BC700, which surpasses other similar catalysts and competing with Pt/C. Hence, the significant kinetic ORR parameters and extended stability (no loss after 5000 potential cycles) of the CeO2/BC700 catalysts provides the promising insight to develop the rare-earth metal oxide nanostructures as a possible candidate for ORR in alkaline medium.

K X-ray fluorescence parameters of some fourth period elements in a magnetic field

The K X-ray fluorescence (XRF) parameters, which are fluorescence cross-section, vacancy transfer probabilities and fluorescence yield, of some fourth-period elements were investigated in an external magnetic field (8000 Gauss). In order to determine the fluorescence parameters, the samples were irritated with 59.54 keV gamma rays from a 241-Americium radioactive source and the rays emitted from the samples were counted in a system consisting of a silicon – lithium drifted detector, multichannel analyzer, magnetic field implementer, and a suitable computer program. The results were studied theoretically and experimentally using the data that were obtained. It was determined that the experimental results were compatible with the theoretical results for measurements without a magnetic field and K XRF parameters changed with the magnetic field.

The magnetic field effect of K X-ray fluorescence parameters of elements in the range 39 ≤ Z ≤ 48

In this work, the fluorescence parameters (the fluorescence cross section (σ), the fluorescence yield (ω), and vacancy transfer probability (η)) of the fifth period elements, which have great potential to be developed as a technology, are investigated by taking advantage of interactions between atoms and radiation. For this process, the samples were excited via 241Am source without magnetic field and in the external magnetic field. The radiation emitted from targets was collected by an Si(Li) detector and energy channels were located on a computer program by means of a multi-channel analyzer. The data on the computer program were analyzed for calculations. The discrepancies have been observed between the experimental results and the theoretical results calculated without magnetic field. It was determined that results changed with the magnetic field (B = 0.4 and 0.8 T) and the variation of the X-ray fluorescence (XRF) parameters with the magnetic field for diamagnetic Ag and Cd is lower than for paramagnetic elements.