3d Vacancies Research Articles

3D oxygen vacancy distribution and defect-property relations in an oxide heterostructure

Oxide heterostructures exhibit a vast variety of unique physical properties. Examples are unconventional superconductivity in layered nickelates and topological polar order in (PbTiO3)n/(SrTiO3)n superlattices. Although it is clear that variations in oxygen content are crucial for the electronic correlation phenomena in oxides, it remains a major challenge to quantify their impact. Here, we measure the chemical composition in multiferroic (LuFeO3)9/(LuFe2O4)1 superlattices, mapping correlations between the distribution of oxygen vacancies and the electric and magnetic properties. Using atom probe tomography, we observe oxygen vacancies arranging in a layered three-dimensional structure with a local density on the order of 1014 cm−2, congruent with the formula-unit-thick ferrimagnetic LuFe2O4 layers. The vacancy order is promoted by the locally reduced formation energy and plays a key role in stabilizing the ferroelectric domains and ferrimagnetism in the LuFeO3 and LuFe2O4 layers, respectively. The results demonstrate pronounced interactions between oxygen vacancies and the multiferroic order in this system and establish an approach for quantifying the oxygen defects with atomic-scale precision in 3D, giving new opportunities for deterministic defect-enabled property control in oxide heterostructures.

3D axial channels and interfacial oxygen vacancies cooperate for enhancing photo-Fenton performance of ZnO/BiOCl microsphere

Boosting photo-Fenton performance by enhancing mass transfer process of peroxy sulphate (PS) and inhibiting the recombination of photo-generation carriers is an appealing strategy. Herein, ZnO/BiOCl porous microsphere assembled by thin nanosheets was successfully fabricated via microwave-assistant method. The results discern that BOZ-30 can eliminate 75.2 % carbamazepine (CBZ, 2.5 mg L−1) in 180 min, which is 1.7 and 1.3 times folder than ZnO and BiOCl, respectively. Moreover, the catalytic mechanism revealed that 3D axial channels and interfacial oxygen vacancies (IOVs) enhance mass transfer process of PS, promote forming of BOZ-PS* complex, and boost the separation efficiency of photo-generated carriers. Therefore, myriad electrons are quickly arrived at surface active sites through thin nanosheets and trapped by BOZ-PS* composites, and then effectively transfer to CBZ. Eventually, PS was activated under the synergistic of IOVs and 3D axial channels. Furthermore, the structure-properties relationship of removal rate, specific area and total oxygen vacancies was established. This work shed a new light on to remove refractory pollution by the cooperation of defect engineering and morphology engineering.

Natural Diatomite Supported Zirconium-Doped TiO2 with Tailoring Band Structure for Enhanced Visible-Light Photocatalytic Properties.

The development of economically applicable, highly efficient and low cost photocatalytic materials has always been a challenge. In this work, we report a zirconium doped TiO/diatomite (ZrTD) composite with enhanced visible light-induced photocatalytic activity. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, UV–VIS diffused reflectance spectroscopy, high-performance liquid chromatography-mass spectrometry, photoluminescence and X-ray photoelectron spectroscopy, respectively. The optimal doping ratio of zirconium into TiO was obtained at 3% (3%ZrTD composite), and the degradation rate constant of which tetracycline (TC) is up to around 8.65 times higher that of zirconium doped TiO. In addition, zirconium doping introduces the impurity levels of Zr 3d and oxygen vacancies into the lattice of TiO, resulting in broadening the light absorption range, reducing the band gap, and improving the separation efficiency of photogenerated electron-hole pairs, thus endowing with visible light photocatalytic properties. Moreover, both the photogenerated holes (h) and superoxide (•O) radicals are responsible for the degradation process of TC, and a possible degradation pathway and the corresponding intermediate products of TC by ZrTD composite are also proposed in detail.

Deep Learning Model for Prediction of Diffusion in Defect Substances

Actual diffusion activity function is an important metric utilized to describe the diffusion activities of a vacancy defect substance. In this paper, we propose a deep learning three-dimensional convolutional CNN model (D3-CNN). A 3D convolution has its kernel slides in three dimensions as opposed to two dimensions with 2D convolutions. 3D convolution is more suitable for three-dimensional data. We also propose an amplification learning technique to predict the actual diffusion activity of a vacancy defect substance, which is impacted by the geometrical parameters of the defect substance and the vacancy distribution function. In this model, the geometric parameters of a three-dimensional constructed vacancy defect substance are generated. The 3D dataset is obtained by the atoms diffusion defect (ADD) simulation model. The geometric parameters of the 3D vacancy defect substance are computed by the proposed amplification technique. The 3D geometric parameters and the diffusion activity values are applied to a deep learning model for training. The actual diffusion activity values of a substance with a vacancy size ranging from size 0.52 mm to 0.61 mm are used for training, and the actual diffusion activity values of substance vacancy of size between 0.41 and 1.01 are classified by the three-dimensional network. The model can realize high speed and accuracy for the actual diffusion activity value. The mean relative absolute errors between the D3-CNN and the ADD models are 0.028–7.85% with a vacancy size of 0.41 to 0.81. For a usual sample with a vacancy of size equal to 0.6, the CPU computation load required by our model is 14.2 × 10−2 h, while the time required is 15.16 h for the ADD model. These results indicate that our proposed deep learning model has a strong learning capability and can function as an influential model to classify the diffusion activity of compound vacancy defect substances.

Effects of 3d transition metal impurities and vacancy defects on electronic and magnetic properties of pentagonal Pd2S4: competition between exchange splitting and crystal fields

In this paper, we first investigate the electronic properties of the two-dimensional structure of dichalcogenide Pd2S4. These properties strongly depend on the crystal field splitting which can change by atomic vacancies (S and Pd vacancies). The main purpose of the present paper is to create remarkable magnetic properties in the system by adding 3d transition metal atoms where the presence of Mn, Cr, and Fe creates the exchange interaction in the system as well as change in the crystal field. The created magnetic properties strongly depend on the competition between exchange interaction and crystal field to separate the levels of d orbitals. In addition, the presence of the transition metals in the structures with S and Pd vacancy has been investigated carefully. The calculations demonstrate that we can achieve an extensive range of magnetic moment up to 3.131 {mu }_{B}. The maximum one is obtained in the presence of Mn and absence of sulfur while some of the doped structures does not have magnetic moment. Our results show that Pd vacancy in the presence of Cr, Mn and Fe metals increases the magnetic property of the Pd2S4 structure. The extensiveness and variety of the obtained properties can be used for different magnetic and non-magnetic applications.

DFT computation of quantum capacitance of transition-metals and vacancy doped Sc2CF2 MXene for supercapacitor applications

MXenes are potential electrode materials in supercapacitors. However, the theoretical investigation of the quantum capacitance (CQ) for transitional-metal (TM) doped MXenes is scarce, and the types of electrode are unclear because of TM doping. Herein, CQ and surface storage charge (Q) of 13 kinds of 3d, 4d, and 5d TM atoms and vacancy doped Sc2CF2, named as TM@PS and VS, are investigated theoretically. The doping of 3d TM atoms can effectively modulate the magnetism of pristine Sc2CF2. CQ and Q of Sc2CF2-based electrode materials are effectively improved and the type of electrode materials is changed because of TM doping. For aqueous and ionic/organic systems, Mn@PS is an excellent anode material, while PS, VS, and Y@PS are more suitable for cathode materials of asymmetric supercapacitors. V@PS, Zr@PS, Nb@PS, Hf@PS, and Ta@PS are more suitable for anode materials in ionic/organic system. Fe@PS is a suitable electrode material of symmetric supercapacitors with high CQ and Q in aqueous system, but a cathode material of asymmetric supercapacitors in ionic/organic system. The results can provide useful information to design and develop the high-performance electrode materials.

Computational screening toward quantum capacitance of transition-metals and vacancy doped/co-doped graphene as electrode of supercapacitors

It is of importance to explore electrode materials with high specific capacitance, improving energy density of supercapacitors. Generally, the composition and structure of electrode materials determines its function. Despite many advantages of graphene, low intrinsic capacitance limits its application in the electrode of supercapacitors. Herein, quantum capacitance of 56 kinds of 3d, 4d and 5d transition-metal and vacancy doped/co-doped graphene, named as TM@G and TM@VG, are screened by density functional theory. We concluded that quantum capacitance (Cq) and density of surface charge (Qsc) of graphene-based electrodes can be effectively enhanced with transition-metal and vacancy co-doping, which can be related to shift and/or enhancement of DOS near the Fermi level. Calculated stability (ΔEb) and Qsc imply that Y@G, Ta@VG, Au@VG and Ni@VG are suitable for anode in aqueous systems, while Sc@VG, Y@VG, Fe@VG and Zn@VG for cathode. Cu@VG and Re@VG are more potential for symmetric supercapacitors. Besides, the capacitive performance of graphene can also be enhanced by transition-metal and vacancy co-doping in ionic/organic systems. Noteworthily, in aqueous/ionic/organic systems, Sc@VG and Y@VG are good cathode materials, when Y@G, Ta@VG and Au@VG are superior candidates for anode materials. Therefore, the selection of electrode materials will hold an instructional significance in the development of suporcapacitors.

Kinetics of the hydrogen defect in congruent LiMO3

We report on the diffusion behaviour of hydrogen through the 3D vacancy network of the LiMO3structure.

Effect of H on the formation of vacancy dislocation loops in α-Fe

Genetic algorithm was applied to search the energy minimization configuration of vacancy clusters in α-Fe. Molecular statics calculations and dynamics annealing relaxation were employed to calculate the formation and binding energies of vacancies and 3D vacancy or vacancy-hydrogen (H) clusters, as well as 2D vacancy or vacancy-H clusters on (111), (011) and (211) planes. Our calculations show that vacancies prefer to form 3D clusters and vacancy dislocation loops are difficult to form, while vacancy-H clusters prefer to shape into 2D clusters, especially on (211) planes. Since H prefers the directional bonding, a vacancy cluster with H atoms tend to form a vacancy dislocation loop with its slip direction along the 〈100〉 direction and on the (211) habit plane. Our results are consistent with the experimental observations, and provide a possible mechanism for the formation of vacancy dislocation loops in α-Fe. Furthermore, we have also explored how dislocation loops trap self-interstitial atoms, vacancies and H atoms. It is of interest to note that H atoms strongly bound to a 〈100〉 vacancy dislocation loop, and are able to enhance the ability for the dislocation loop to further trap vacancies and reduce its ability to absorb self-interstitial atoms, thus promoting the growth of the 〈100〉 vacancy dislocation loops.

Beyond ideal two-dimensional metals: Edges, vacancies, and polarizabilities

Recent experimental discoveries of graphene-stabilized patches of two-dimensional (2D) metals have motivated also their computational studies. However, so far the studies have been restricted to ideal and infinite 2D metallic monolayers, which is insufficient because in reality the properties of such metallic patches are governed by microstructures pervaded by edges, defects, and several types of perturbations. Here we use density-functional theory to calculate edge and vacancy formation energies of hexagonal and square lattices of 45 elemental 2D metals. We find that the edge and vacancy formation energies are strongly correlated and decrease with increasing Wigner-Seitz radii, analogously to surface energies. Despite a radical reduction in atomic coordination numbers, the 2D and 3D vacancy formation energies and work functions are nearly the same for each metal. Finally, static polarizabilities reveal a clear cubic dependence on bond length. These trends provide useful insights when moving towards reality with elemental 2D metals.

Charge state effect on K-shell ionization of silicon induced by iodineq+ ions

In near Bohr velocity ion-atom collisions, a dependence of target K-shell ionization cross sections upon the ionic charge states has been observed. Experiments were performed in silicon solid target with 2–5 MeV iodineq+ ions incident in charge states +20 to +25. K-shell ionization cross section of silicon for q = 20 and 22 iodine ions impact with the same incident energy are almost equal, and are well described by the theory of binding-energy-modified BEA. However, for q = 25 iodine ions collisions, 3d vacancies of projectile transfer to the 1s orbit of target atom via rotational coupling of 3dπ, δ-3dσ molecular orbits in the framework of quasi-molecular model, which results in an increase of the K-shell ionization cross section of silicon.

Nature-Inspired 2D-Mosaic 3D-Gradient Mesoporous Framework: Bimetal Oxide Dual-Composite Strategy toward Ultrastable and High-Capacity Lithium Storage.

In allusion to traditional transition-metal oxide (TMO) anodes for lithium-ion batteries, which face severe volume variation and poor conductivity, herein a bimetal oxide dual-composite strategy based on two-dimensional (2D)-mosaic three-dimensional (3D)-gradient design is proposed. Inspired by natural mosaic dominance phenomena, Zn1-xCoxO/ZnCo2O4 2D-mosaic-hybrid mesoporous ultrathin nanosheets serve as building blocks to assemble into a 3D Zn-Co hierarchical framework. Moreover, a series of derivative frameworks with high evolution are controllably synthesized, based on which a facile one-pot synthesis process can be developed. From a component-composite perspective, both Zn1-xCoxO and ZnCo2O4 provide superior conductivity due to bimetal doping effect, which is verified by density functional theory calculations. From a structure-composite perspective, 2D-mosaic-hybrid mode gives rise to ladder-type buffering and electrochemical synergistic effect, thus realizing mutual stabilization and activation between the mosaic pair, especially for Zn1-xCoxO with higher capacity yet higher expansion. Moreover, the inside-out Zn-Co concentration gradient in 3D framework and rich oxygen vacancies further greatly enhance Li storage capability and stability. As a result, a high reversible capacity (1010 mA h g-1) and areal capacity (1.48 mA h cm-2) are attained, while ultrastable cyclability is obtained during high-rate and long-term cycles, rending great potential of our 2D-mosaic 3D-gradient design together with facile synthesis.

L-edge sum rule analysis on 3d transition metal sites: from d10 to d0 and towards application to extremely dilute metallo-enzymes.

According to L-edge sum rules, the number of 3d vacancies at a transition metal site is directly proportional to the integrated intensity of the L-edge X-ray absorption spectrum (XAS) for the corresponding metal complex. In this study, the numbers of 3d holes are characterized quantitatively or semi-quantitatively for a series of manganese (Mn) and nickel (Ni) complexes, including the electron configurations 3d10→ 3d0. In addition, extremely dilute (<0.1% wt/wt) Ni enzymes were examined by two different approaches: (1) by using a high resolution superconducting tunnel junction X-ray detector to obtain XAS spectra with a very high signal-to-noise ratio, especially in the non-variant edge jump region; and (2) by adding an inert tracer to the sample that provides a prominent spectral feature to replace the weak edge jump for intensity normalization. In this publication, we present for the first time: (1) L-edge sum rule analysis for a series of Mn and Ni complexes that include electron configurations from an open shell 3d0 to a closed shell 3d10; (2) a systematic analysis on the uncertainties, especially on that from the edge jump, which was missing in all previous reports; (3) a clearly-resolved edge jump between pre-L3 and post-L2 regions from an extremely dilute sample; (4) an evaluation of an alternative normalization standard for L-edge sum rule analysis. XAS from two copper (Cu) proteins measured using a conventional semiconductor X-ray detector are also repeated as bridges between Ni complexes and dilute Ni enzymes. The differences between measuring 1% Cu enzymes and measuring <0.1% Ni enzymes are compared and discussed. This study extends L-edge sum rule analysis to virtually any 3d metal complex and any dilute biological samples that contain 3d metals.

Evolution of Vacancy-Type Defects, Phase Transition, and Intrinsic Ferromagnetism during Annealing of Nanocrystalline TiO2 Studied by Positron Annihilation Spectroscopy

The evolution of vacancy-type crystalline defects across the transition from anatase to rutile structure of titanium dioxide (TiO2) nanoparticles during high-temperature annealing in oxygen and argon is studied by using positron lifetime and coincidence Doppler broadening spectroscopic measurements. The TiO2 nanoparticles were synthesized through a simple sol–gel chemical route. The changes in the crystalline phase and lattice parameters of the nanoparticles upon thermal treatment were investigated by X-ray diffraction and high-resolution transmission electron microscopy, and the results were correlated with those of photoluminescence spectroscopy and positron annihilation measurements. The structural defects, mostly 3D vacancy clusters, in the nanoparticles were found to decrease in concentration during the annealing in O2 rather than in Ar at elevated temperatures. In the case of annealing in Ar, the vacancy-type defects persisted even at the highest annealing temperature of 900 °C used in the experimen...

Charge state effect on K-shell ionization of aluminum by 600–3400 keV xenonq+ (12 &lt; q &lt; 29) ion collisions

K-shell X-ray spectra of Al were measured by the interaction of 600–3400 keV Xe q+ (q = 12–29) ions with Al surface. The X-ray yields per incident ion were deduced and the K-shell ionization cross-sections were obtained from the experimental yield data. With the same incident energy, the K-shell ionization cross-sections of Al excited by Xe q+ (q < 26) ions were of the same order of magnitude, while for q = 26 and 29 Xe ion collisions, they were, respectively, about two and ten times larger. Taking into account the binding-energy-modification and the recoil effect of target atoms, the binary encounter approximation (BEA) theory was consistent with the experimental data for q < 26 Xe ion collisions, but it underestimated those excited by q = 26 and 29 Xe ions. This indicates that the K-shell ionization of target induced by Xe q+(q < 26) ions was mainly due to the direct Coulomb excitation. However for q = 26 and 29 Xe ions collisions, the transfer of 3d vacancies of projectile to the 1s orbital of target via rotational coupling of the 3dπ, δ-3dσ molecular orbitals, which were formed in the ion-atom quasi-molecule, may cause a considerable contribution to the enhancement of ionization. In addition to the well known Auger and X-ray transition, our experiments proved that the molecular orbital transition (“side-feeding”) mechanism is also a significant channel for de-excitation of hollow atoms formed below the surface.

5p-4d Emission spectrum with a cascade decay of the 3d vacancy in the Xe atom

The 5p-4d emission spectrum, obtained during cascade de-excitation of the initial deep 3d vacancy in the Xe atom, was calculated by directly constructing a decay tree in a stepwise manner. The cascade decay tree was constructed with allowance for all radiative and nonradiative channels of decay for the initial and all intermediate ionic configurations of the cascade. The probabilities of branching and transition energies were calculated in a one-electron approximation with averaging over configurations. The 5p-4d cascade emission spectrum has a complex structure with many components, which reflects the transitions from the wide variety of the many-hole intermediate configurations generated by the cascade. The calculated data agree well with the experiment.

Dynamics of electron emission in double photoionization processes near the krypton 3d threshold

Two-electron emission following photoabsorption near the Kr 3d threshold is investigated both experimentally and theoretically. On the experimental side, electron/electron coincidences using a magnetic bottle time-of-flight spectrometer allow us to observe the complete double photo ionization (DPI) continua of selected Kr2+ final states, and to see how these continua are affected by resonant processes in the vicinity of the Kr 3d threshold. The analysis is based on a quantum mechanical approach that takes into account the contribution of three different processes: (A) Auger decay of the inner 3d vacancy with the associated post-collision interaction (PCI) effects, (B) capture of slow photoelectrons into discrete states followed by valence multiplet decay (VMD) of the excited ionic states and (C) valence shell DPI. The dominant process for each Kr2+(4p−2) final state is the photoionization of the inner shell followed by Auger decay of the 3d vacancies. Moreover, for the 4p−2(3P) and 4p−2(1D) final ionic states an important contribution comes from the processes of slow photoelectron capture followed by VMD as well as from double ionization of the outer shell involving also VMD.

Mg-doped LiNi 0.5Mn 1.5O 4 spinel for cathode materials

Lithium-ion batteries are becoming more and more important not only for portable electronic devices, but also in prevision of high power electric vehicles. In such an optic, deep studies regarding all the components of a secondary battery are in development. In this study, high voltage cathode materials have been selected. Crystals with spinel structure have a 3D vacancy pathway suitable for Li-ions transport. The material under study was LiNi 0.5Mn 1.5O 4 doped with magnesium replacing the nickel. Various samples were synthesized via three different routes: a solid-state method, a modified sol–gel method and a xerogel method. The structure and morphology of the powders were analyzed with HRTEM and XRD. Electrochemical tests were also performed. A wide range of particle sizes (from micro to nanosize) was the result of the different synthesis routes. Unfortunately pure materials were not always obtained. The electrochemical tests showed improvement of the material's cyclability, by reducing the particle size. The electrochemical tests further confirmed the existence of a Li 1+ d Mn 2− d O 4 impurity. The results are quite promising, however, further improvement of the purity of the electrode composition are needed.

Generalized oscillator strengths for the3delectrons of Cs, Ba, and Xe: Effects of spin-orbit-activated interchannel coupling

This paper investigates for the first time ever the use of the spin-orbit interaction to probe correlation effects in the generalized oscillator strength (GOS) of the 3d subshells of Cs, Ba, and Xe, viz. we study how the GOSs of the Cs, Ba, and Xe 3d{sub 3/2} and 3d{sub 5/2} levels are affected by the intradoublet correlations. The calculations are carried out using the Hartree-Fock approximation and within the framework of a modified version of the spin-polarized random phase approximation with exchange, which takes into account multielectron correlation effects. The effects of relaxation of the excited electrons due to the creation of the 3d vacancy are also accounted for. Our GOS results for Cs, Ba, and Xe, obtained for values of the momentum transfer q from 0 to 4 a.u. and energy transfer {omega} from 0.1 to 8 Ry, demonstrate the strong interaction between the components of the spin-orbit doublet of the 3d electrons in Cs, Ba, and Xe. This leads to the appearance of an additional maximum in the GOS for the 3d{sub 5/2} subshell, due to the action of the 3d{sub 3/2} electrons. Additionally, for the dipole transition in Cs and Ba, the 3d{sub 5/2} subshell perturbs the more » 3d{sub 3/2} strongly for q=4 a.u. only, while in Xe, the perturbation is at the {omega} value of approximately 58 Ry for all considered q values. It is concluded that the intradoublet correlations are generally very important in the dipole, monopole, and quadrupole transitions, but particularly in the dipole transition. « less

Auger Spectra and Different Ionic Charges Following 3s, 3p and 3d Sub-Shells Photoionization of Kr Atoms

The decay of inner-shell vacancy in an atom through radiative and non-radiative transitions leads to final charged ions. The de-excitation decay of 3s, 3p and 3d vacancies in Kr atoms are calculated using Monte-Carlo simulation method. The vacancy cascade pathway resulted from the de-excitation decay of deep core hole in 3s subshell in Kr atoms is discussed. The generation of spectator vacancies during the vacancy cascade development gives rise to Auger satellite spectra. The last transitions of the de-excitation decay of 3s, 3p and 3d holes lead to specific charged ions. Dirac-Fock-Slater wave functions are adapted to calculate radiative and non-radiative transition probabilities. The intensity of Kr 4+ ions are high for 3s hole state, whereas Kr 3+ and Kr 2+ ions have highest intensities for 3p and 3d hole states, respectively. The present results of ion charge state distributions agree well with the experimental data.