A Study on Oxygen Vacancy Resistance Mechanism of V2O5

Mixed Ionic Electronic Conducting (MIEC) transition metal oxide (ABO3) perovskites are utilized for catalytic,1 energy conversion,2,3 and other applications. The oxygen ionic conductivity of these MIECs depends on their oxygen vacancy concentration and ionic mobility. In turn, the oxygen ion concentration and mobility both depend on the charge of the B-site atom,4 which itself depends on factors such as the A site La/Sr ratio, the crystal structure, etc. Previous calculations demonstrated that the Fe atom charge state distribution observed in strontium ferrite (SrFeO3-δ) is caused by differences in the d-orbital splitting of octahedral (Oh) versus square pyramidal (SP) Fe-O coordination (Figure 1).5 This d-orbital splitting ensures that the two electrons left behind when a charge-neutral oxygen vacancy forms in cubic SrFeO3-δ are transferred to the second nearest Fe neighbors,5 resulting in a large oxygen vacancy polaron size that produces strong oxygen vacancy interactions at high oxygen nonstoichiometry. As a result, the oxygen vacancy formation energy increases with oxygen nonstoichiometry in cubic SrFeO3-δ.5 Previous calculations also demonstrated that in orthorhombic lanthanum ferrite (LaFeO3-δ) the formation of a neutral oxygen vacancy produces a polaron that is localized to the oxygen-vacancy-adjacent Fe atoms. Hence, in orthorhombic LaFeO3-δ the oxygen vacancies do not interact with increasing oxygen nonstoichiometry.6 The objective of the present work was to examine whether d-orbital splitting could also explain the oxygen vacancy behavior of other MIEC perovskites. Hence, the impact of d-orbital splitting on oxygen vacancy polaron size and formation energies in lanthanum strontium manganite and lanthanum strontium cobaltite were modeled for the first time. Here, the charge redistribution caused by oxygen vacancy formation was studied for six different compositions: LaFeO3-δ, SrFeO3-δ, LaMnO3-δ, SrMnO3-δ, LaCoO3-δ, and SrCoO3-δ. The GGA+U method with PAW potentials implemented in VASP was utilized for all the structural energy calculations. First, the Hubbard-U parameter was calibrated to describe the charge on the B-site atom (U = 3 was selected for Fe, as done previously).6 The oxygen vacancy formation energy as a function of oxygen non-stoichiometry (δ) was then calculated at 0 K in vacuum by varying the size of the supercell, with oxygen vacancy interactions being enabled by the periodic boundary conditions. The calculated polaron size for neutral-oxygen-vacancy–containing ABO3 structures are summarized in Table 1.In LaMnO3-δ, Mn3+ has an [Ar] 3d4 electronic configuration in Oh coordination. After the formation of a neutral oxygen vacancy, the two Mn atoms adjacent to the oxygen vacancy go from Oh to SP coordination and the excess electrons left behind by the removed oxygen are pushed to the a1g level of the second nearest neighboring Oh-Mn (instead of remaining localized to the b1g level of the SP-Fe). This long range charge transfer results in large polaron size. This behavior is in contrast with that of LaFeO3-δ. However, LaMnO3-δ and SrFeO3-δ exhibit comparable polaron sizes since Fe4+ has an [Ar] 3d4 electronic- configuration. In SrMnO3-δ, Mn4+ has a [Ar] 3d3 electronic configuration in Oh coordination. Therefore, the formation of a neutral oxygen vacancy localizes the electrons to the oxygen vacancy adjacent Mn atoms, producing a small polaron, as explained by the d-orgbial splitting in Figure 1. This d-orbital splitting analysis indicates that the polaron size in LSM > LSF > LSC. Additional work aimed at calculating the oxygen vacancy formation energies of other ABO3 compositions are in progress.

Formation and transfer of oxygen vacancies are essential to transitional metal oxide RRAM’s switching behavior. In this paper, first principle is used to simulate the formation energy of oxygen vacancies in undoped, Al-doped and N-doped TaOx based RRAM. In Al-doped TaOx, oxygen vacancies’ formation energy is reduced significantly near the dopant atom. However, in N-doped TaOx, the formation energy of oxygen vacancies is slightly decreased compared with the undoped one. Our simulation results provide insight and guidance on the approach to improving RRAM’s performance by doping atoms.

High-entropy perovskite oxides (HEPOs) have emerged as a promising class of materials for use in solid oxide electrolyzer cells (SOECs), particularly as oxygen electrodes, due to their excellent thermal and chemical stability. The concentration of oxygen vacancies in HEPOs directly impacts critical properties such as ionic conductivity, thermal expansion, and overall electrochemical behavior. Despite their importance, predicting how the oxygen vacancy concentration in HEPOs varies with five or more metal cation dopants and temperature remains elusive, as the net energy needed to remove a lattice oxygen is significantly complicated by variations from different metal cations and configurational entropy.In this work, we investigate how oxygen vacancy concentrations are affected by low-entropy (LE, 2–3 cations) and high-entropy (HE, 5+ cations) A-site compositions in perovskite oxides. We synthesized 14 compositions, inspired by the state-of-the-art SOEC material lanthanum strontium cobalt ferrite (LSCF), using solution combustion synthesis and measured changes in oxygen vacancy concentration between 500–1000°C via thermogravimetric analysis. Using established defect models, we estimated and compared the oxygen vacancy formation enthalpy (ΔH) and entropy (ΔS).Our results confirm the expected role of divalent A-site cations in facilitating oxygen vacancy formation. However, substantial variation was observed among HE samples with identical divalent cation concentrations, suggesting additional influencing factors. We identify the variance in A-site ionic radii as a key compositional descriptor that strongly correlates with oxygen vacancy thermodynamics. HE samples with larger A-site size variance consistently exhibited lower ΔH and ΔS of oxygen vacancy formation, as well as more linear oxygen vacancy growth with temperature compared to their LE counterparts.To investigate the origin of this behavior, we conducted high-throughput atomistic simulations using a machine-learned universal interatomic potential. We computed the energy required to form an oxygen vacancy across hundreds of oxygen sites in large supercells (1280 atoms) for each material. While the average vacancy formation energies were comparable between LE and HE samples, HE compositions exhibited a broader distribution of vacancy formation energies due to the local strain induced by size mismatches between A-site cations.We developed a statistical thermodynamic model to analyze how variations in formation energy impact a material's equilibrium oxygen vacancy concentration. By treating oxygen sites as a distribution of energy states, we derived analytical expressions for formation ΔH and ΔS as a function of vacancy energy variance. The results show that broadening the vacancy energy distribution leads to a decrease in both formation enthalpy and configurational entropy, consistent with experimental data. Notably, the model predicts a scaling relation between ΔHf and ΔSf, explaining the experimentally observed correlation between LE and HE samples.In summary, our combined experimental, computational, and theoretical approach reveals that A-site cation disorder—quantified by size variance—plays a crucial role in determining the thermodynamics of oxygen vacancy formation in HEPOs. This disorder induces variation in oxygen vacancy formation energies, which lowers the formation enthalpy (ΔH) and entropy (ΔS), leading to greater oxygen vacancy populations at lower temperatures. The findings establish A-site size variance as a practical and predictive design parameter for tuning defect behavior in complex oxides. This framework advances our understanding of defect chemistry in disordered systems and provides guidance for engineering functional materials for SOECs, catalysis, and beyond. Figure 1

The formation and migration energies of oxygen vacancies in pure BaTiO3, and BaMxTi1−xO3 (M = Zr, Ge) are calculated by first-principles calculations to understand the effect of doping on the reliability of multilayer ceramic capacitors (MLCCs). The formation and migration energies of oxygen vacancies are found to be larger in BaZrxTi1−xO3 than in BaTiO3. This finding could be one of the possible reasons behind the improved reliability of Zr-doped MLCCs materials. On the other hand, by substituting Ge, the migration energy of BaGexTi1−xO3 becomes larger than that of BaTiO3. This is despite the smaller oxygen vacancy formation energy in BaGexTi1−xO3 than in BaTiO3. Even though Zr and Ge are tetravalent in BaMxTi1−xO3, their valence states are different after the formation of oxygen vacancies, providing an explanation for the differences in vacancy formation and migration energies between BaZrxTi1−xO3 and BaGexTi1−xO3. Our theoretical results are further confirmed by experiments on these model systems.

Due to the high dielectric constant and wide band gap, ZrO2has become a widely used gate dielectric material in complementary metal-oxide-semiconductor devices, and the ZrO2/Si interface plays a critical role in determining overall device performance. In this work, we systematically study the effects of oxygen vacancy defects on the band structure, band offset, and charge transfer in cubic ZrO2/Si (c-ZrO2/Si) interface structure. Our results reveal that the constructed (c-ZrO2)9/(Si)9interface is an indirect band gap semiconductor, with the band edges contributed by Si and a band offset greater than 2 eV. The three oxygen vacancy defects reduce the band gap and induces quasi-flat band. The band offset is partially influenced by the location of oxygen vacancies, but the valence band offset and conduction band offset always exceed 1 eV. Notably, theVO1andVO2alter the bonding environment and charge transfer of adjacent Si atoms, whereasVO3, located farther from the interface, preserves the native charge transfer characteristics of the (c-ZrO2)9/(Si)9interface. TheVO10defect exhibits the lowest formation energy across all conditions, with the value in O-poor conditions being 6.992 eV lower than that in the O-rich environment. These findings suggest that the presence of oxygen vacancies may significantly affect the electrical and carrier properties of c-ZrO2/Si interface, providing theoretical insights into optimizing the design and fabrication of Si-based semiconductor devices.

Introduction Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell (SOFC). For a high catalytic activity, the improvement of properties governing the cathode performance is important. It is generally regarded that one of the important factors is electronic structure of cathode material. It is known that the Co ion in doped lanthanum cobaltite shows three spin states, such as low spin (LS), intermediate spin (IS), and high spin (HS). Hong et al. pointed out that the change of electronic structure due to the difference of spin states affect the formation energy of oxygen vacancy in LaCoO3 bulk system. Although it is expected that the high catalytic materials for oxygen adsorption and dissociation on oxide surface are proposed by the controlling the electronic structure of doped lanthanum cobaltite, the effect of electronic structure due to the difference of spin states of Co ion is unclear for the surface reactions on doped lanthanum cobaltite. In this study, we analyzed the stability of oxygen vacancy and surface reaction of oxygen under the different spin states of Co ion in Sr doped LaCoO3by using density functional theory (DFT) calculation. Computational Details We used LaSrO-terminated (001) surface of cubic LaSrCoO3 crystal structure. Half of La atoms were substituted by Sr atoms in LaO layers to analyze the effect of segregation of Sr in La6Sr6Co8O28 slab model. GGA-PBE with PAW potentials were applied with cutoff energy of 600 eV and 2x2x1 k-points. The initial spin configuration was constrained, such as LS, IS, and HS states, to obtain the different electronic structures. All DFT calculations were performed by using VASP. Results and Discussion We first analyzed the oxygen vacancy formation energy on the surface of La6Sr6Co8O28. The vacancy formation energies of one oxygen on surface under the LS, IS, and HS states were 0.92, 1.03, and 0.95 eV, respectively. The vacancy formation energies of two oxygen on surface under the LS, IS, and HS states were 3.27, 2.36, and 1.90 eV, respectively. The oxygen vacancy formation became unstable when the number of oxygen vacancy increases in all spin states. The oxygen vacancy formation energy for HS was the smallest compared with LS and IS states for two oxygen vacancy systems. We found that the difference of spin state of Co ion affects the oxygen vacancy formation energy on surface of LaSrCoO3. In addition, we analyzed the stability of oxygen vacancy under the different Sr configurations to understand the effect Sr segregation. Details are discussed in the presentation. Acknowledgement The activities of INAMORI Frontier Research Center are supported by KYOCERA Corporation. All calculations are performed on the HA8000 computer systems in Research Institute for Information Technology, Kyushu University. Reference [1] W. T. Hong, M. Gadre, Y. -L. Lee, M. D. Biegalski, H. M. Christen, D. Morgan, and Y. Shao-Horn, J. Phys. Chem. Lett., 4, 2493 (2013).

We employ density functional theory to investigate the effect of A-site rare earth substitution on the point defect formation in bismuth titanate (BIT) in the dilute substitution limit. Despite previous claims that the formation energy of neutral oxygen vacancies in La-substituted BIT (BLT) is higher than in pure BIT, our calculations show that this is only true for four out of the six distinct oxygen sites. Of these four sites, in two the difference is <0.1 eV while in the other two the difference is ~0.25 eV. In the case of +2 charged oxygen vacancies, in only two of the six distinct oxygen sites is the formation energy of the oxygen vacancy higher in BLT than in BIT, where they differ by ~0.14 eV. These results do not support the traditional explanation for the fatigue-free characteristic of BLT, which states that La substitution might avoid the ferroelectric fatigue of BIT by simply suppressing the formation of oxygen vacancies.

The interaction between oxygen vacancies and doping atoms in ZnO

Preparation of Zn1-xCexO resistive switching film on SS304 and its corrosion resistance mechanism in NaCl solution

Introduction Mixed Ionic Electronic Conducting (MIEC) perovskite materials are used for high-performance gas separation membranes,1 gas sensing electrodes,2 solid oxide fuel cell (SOFC) catalysts,3 and photoelectrodes.4 SrFeO3-δ is a prototypical member of this perovskite family possessing large oxygen vacancy and electronic carrier concentrations due to the reaction:5 Oo x = Vo ** +2e/ +1/2O2(g) (1) Unfortunately, even though SrFeO3-δ shows a large variation in oxygen nonstoichiometry (0-0.5) over a broad temperature range (0 – 1400 oC) in air,6 vacancy-ordering-induced phase transitions (from cubic to tetragonal to orthorhombic to brownmillerite, with increasing temperature) decrease the oxygen ion conductivity through a reduction in the number of mobile oxygen sites.6 In this study, a combined density functional theory (DFT) + thermodynamics approach was used to reveal the relationship between oxygen vacancy formation and the charge states of Fe in various SrFeO3-δcrystal structures as the oxygen nonstoichiometry was varied from 0-0.5. Computational Methods Here a DFT based approach with the GGA+U method implemented in VASP was utilized for the energy calculations. A U parameter of 3 was selected based on computational agreement with the experimental magnetic moments and lattice parameters of perfect SrFeO3 and LaFeO3 (indicating that this U paramter could be used to describe both Fe4+ and Fe3+ in these structures). A total Bader charge analysis was not able to differentiate the charge states of Fe in these structures. Therefore, a linearly-interpolated magnetic moment interpreted iron oxidation state was determined by assigning the calculated magnetic moments of Fe in SrFeO3 (3.61 μB) and Fe in LaFeO3 (4.23 μB) to a Fe charge of 4+ and 3+ respectively. As shown in Figure 1, the Fe oxidation state change caused by the operation of Eqn. 1 was determined using a 4x4x4 supercell. After determining the oxygen vacancy formation site within each SrFeO3-δstructure (i.e. the site with the lowest oxygen vacancy formation energy), the supercell size was varied to calculate the vacancy formation energy at various oxygen vacancy site fractions. A thermodynamic method was then developed to predict the oxygen vacancy site fraction and oxygen nonstoichiometry at SOFC-relevant temperatures and oxygen partial pressures. Results and Discussion Perfect cubic SrFeO3 contains all its Fe in octahedral coordination with 4+ charge and no tilt exists between these octahedra. As shown in Figure 1, the formation of a single oxygen vacancy in cubic SrFeO3 creates two square pyramidal Fe-O coordination polyhedra adjacent to an oxygen vacancy. Further, the computational results show that within each SrFeO3-δ structure, oxygen vacancies are always formed at the site shared by the two highest charged Fe atoms. Figure 1 also illustrates a new long-range charge transfer phenomena whereby electrons left by the oxygen vacancy are transferred to the second nearest neighbor iron atoms (not those directly connected to the oxygen vacancies). This long-range charge transfer causes strong oxygen vacancy interactions that 1) lead to the oxygen formation energy increasing with oxygen nonstoichiometry and 2) contribute to oxygen vacancy induced phase transformations. To fully describe the interacting oxygen vacancies, a new numerical method treating both dilute and non-dilute point defect concentrations was developed. The good agreement between the predicted and experimentally-reported oxygen vacancy nonstoichiometry over the 300-1300oC range in air demonstrates the robustness of this approach. Conclusions These calculations resolve a long-standing debate in the literature on the mixed charge states of Fe in SrFeO3-δand explain the origin of the oxygen vacancy interactions in this material. Furthermore, the predicted oxygen vacancy concentration (not the total nonstoichiometry) decreases above 600˚C, causing a loss of oxygen conductivity.

Disordered Rock-Salt (DRX) cathode structures are materials where lithium and transition metal atoms are arranged in a disordered solid solution. These structures are currently under intensive study [1] due to their potential higher energy density, bigger capacity than the typical layered cathode structure, and improved flexibility in the selection of raw materials. Driven by this, we have recently compiled a DFT-based database of DRX structures with over 6,000 different metal oxide compositions. Moreover, since oxygen loss is linked to voltage degradation, intergranular cracks, and irreversible phase transformation, developing a descriptor that allows us to understand and reflect the stability of oxygen within the DRX anion lattice is crucial. It represents a significant research challenge that our study aims to address.In this work, we study two things: First, since the generation of oxygen vacancies holds a critical value in elucidating the stability of cathode material oxides[2], our methodology focuses on generating an extensive DFT database of over 1,400 oxygen vacancy formation energies (Evf(O)) from selected DRX structures. We then employ a machine learning (ML) model to predict the Evf(O) and their distribution for a variety of different compositions. The ML model incorporates site-specific features, such as the maximum reduction potential of the cations neighboring the O vacancy, the O p-band center of mass, and information from atomic population analysis (such as the bond order and the bond spin polarization between each O and its nearest neighbors). This approach is necessary because the DRX structure contains different local environments where O vacancies could be created, and recent work from Baldassarri et al. has highlighted the limitations of ML models that only include global features and lack their ability to differentiate the behavior of compounds containing the same elements but in different oxidation states [3]. This allows us to predict the O vacancies energetics with an accuracy comparable to DFT and to develop a descriptor to classify different compositions of DRX structures.Second, given that oxygen destabilizes during delithiation, we analyze the impact and relationship of the Li vacancy formation energies (Evf(Li)) and Evf(O) of each O able to create a vacancy. The results show a strong interaction between these energetics, and in particular, an inverse correlation between Evf(O) of a specific O site and the Evf(Li) of the Li atoms that surround this O, which within these DRX prototypes the number of surrounding Li varies from 1 to 5. In line with what others proposed [4], there is a strong interaction between these two vacancy types. However, we expect that the generation of O vacancies is determined not only by their thermodynamic driving force but also by the displacement/migration of the nearest neighbor lithium (NN-Li) that surrounds each O.The methodology and fundamental understanding developed in this study about DRX O-vacancies and their relationship with NN-Li during delithiation could help investigate and describe compositionally similar transition metal oxide cathodes belonging to the same crystal structure family (layered, spinel-like, γ-LiFeO2). Hence, this research not only enhances our understanding of these materials but also paves the way for the design and development of more flexible and stable energy storage systems.[1] S. Anand, B. Ouyang, T. Chen, G. Ceder, Impact of the energy landscape on the ionic transport of disordered rocksalt cathodes, Physical Review Materials 7(9) (2023) 095801.[2] H. Zhang, B.M. May, F. Omenya, M.S. Whittingham, J. Cabana, G. Zhou, Layered Oxide Cathodes for Li-Ion Batteries: Oxygen Loss and Vacancy Evolution, Chemistry of Materials 31(18) (2019) 7790-7798.[3] B. Baldassarri, J. He, A. Gopakumar, S. Griesemer, A.J.A. Salgado-Casanova, T.-C. Liu, S.B. Torrisi, C. Wolverton, Oxygen Vacancy Formation Energy in Metal Oxides: High-Throughput Computational Studies and Machine-Learning Predictions, Chemistry of Materials 35(24) (2023) 10619-10634.[4] C. James, Y. Wu, B.W. Sheldon, Y. Qi, The impact of oxygen vacancies on lithium vacancy formation and diffusion in Li2-xMnO3-δ, Solid State Ionics 289 (2016) 87-94.

The defect stability in a prototypical perovskite oxide superlattice consisting of SrTiO$_3$ and PbTiO$_3$ (STO/PTO) is determined using first principles density functional theory calculations. Specifically, the oxygen vacancy formation energies E$_v$ in the paraelectric and ferroelectric phases of a superlattice with four atomic layers of STO and four layers of PTO (4STO/4PTO) are determined and compared. The effects of charge state, octahedral rotation, polarization, and interfaces on the E$_v$ are examined. The formation energies vary layer-by-layer in the superlattices, with E$_v$ being higher in the ferroelectric phase than that in the paraelectric phase. The two interfaces constructed in these oxide superlattices, which are symmetrically equivalent in the paraelectric systems, exhibit very different formation energies in the ferroelectric superlattices and this can be seen to be driven by the coupling of ferroelectric and rotational modes. At equivalent lattice sites, E$_v$ of charged vacancies is generally lower than that of neutral vacancies. Octahedral rotations (a$^0$a$^0$c$^-$) in the FE superlattice have a significant effect on the E$_v$, increasing the formation energy of vacancies located near the interface but decreasing the formation energy of the oxygen vacancies located in the bulk-like regions of the STO and PTO constituent parts. The formation energy variations among different layers are found to be primarily caused by the difference in the local relaxation at each layer. These fundamental insights into the defect stability in perovskite superlattices can be used to tune defect properties via controlling the constituent materials of superlattices and interface engineering.

In this paper, density functional theory (DFT) calculations of formation energy and relaxed structure were performed in W-doped HfO 2 system, and electrical levels of oxygen vacancy and vacancy chain were also compared in monoclinic HfO 2 . The simulation shows that the formation energy of threefold and fourfold oxygen vacancy in the vicinity of W atom is lower compared to dopant-free monoclinic HfO 2 . However, the formation energy of oxygen vacancy far from dopant keeps the same. The dopant W atom makes the oxygen vacancy states shifted downward, and at the same time, the shallow level of 5d states may cause the electrons more easily to be thermally activated to be free conduction carriers.

Oxygen vacancies play a crucial role in determining the catalytic properties of Ce-based catalysts, especially in oxidation reactions. The design of catalytic activity requires keen insight into oxygen vacancy formation mechanisms. In this work, we investigate the origin of oxygen vacancies in CeO2 from the perspective of electron density via high-energy synchrotron powder x-ray diffraction. Multipole refinement results indicate that there is no obvious hybridization between bonded Ce and O atoms in CeO2. Subsequent quantitative topological analysis of the experimental total electron density reveals the closed-shell interaction behavior of the Ce–O bond. The results of first-principles calculation indicate that the oxygen vacancy formation energy of CeO2 is the lowest among three commonly used redox catalysts. These findings indicate the relatively weak bond strength of the Ce–O bond, which induces a low oxygen vacancy formation energy for CeO2 and thus promotes CeO2 as a superior catalyst for oxidation reactions. This work provides a new direction for design of functional metal oxides with high oxygen vacancy concentrations.

Oxygen vacancies play significant roles in various properties of oxide materials. Therefore, insights into the oxygen vacancies can facilitate the discovery of better oxide materials. To achieve this, we developed codes for high-throughput point-defect calculations and applied them to characterize oxygen vacancies in 937 oxides. From the resulting large dataset, we analyzed the vacancy structures and formation energies and constructed machine-learning regression models to predict vacancy formation energies. We have found that the vacancy formation energies are predicted using the random forest regression models with accuracies of 0.27--0.44 eV depending on the charge states. Analyses of the importance of the descriptors show that the formation energies of the neutral vacancies are mainly determined by the orbital characteristics of the conduction-band minima, the oxide stability, and the band gaps, whereas those of the doubly charged defects are determined by factors related to electrostatic energy. These codes and datasets are publicly available, and a graphical user interface is available to analyze the calculation results.