Properties Of Oxygen Vacancies Research Articles

Diamagnetic to Ferromagnetic Like Transition of Non-Stoichiometry Barium Titanate (BaTiO3-x) Prepared by Sol-gel Method

The oxygen vacancy properties are significant, creating ferromagnetic properties of material in metal oxide systems like dilute magnetic semiconductors. An aqueous sol-gel method has been used in the present study to synthesize non-stoichiometry BaTiO3-x polycrystalline. In an attempt of examining the oxygen deficiency consequences on the magnetic properties, the gel samples were sintered (1000◦C) at various times (6, 12, 18, and 24 hours) under a vacuum environment. This study employs an X-ray diffraction apparatus in terms of characterizing segments and structures of the samples. It also investigates morphology and element distribution on the surface of the samples exploiting an Electron microscope where Energy dispersive spectroscopy is supplied. For the purpose of characterizing the magnetic properties of the samples, it applies vibrating sample magnetometers. The chemical state of the element and its corresponding bond to other elements was identified using X-ray photoelectron spectroscopy. Single-phase compounds were observed. The crystal system is tetragonal, but the crystal parameters are different. Increase sintering time leads to increase crystallite size and decrease in micro strain. Moreover, sintering in a vacuum environment results in oxygen deficiency and leads to the atomic ratio of Ba/Ti change as the sintering time increases. The Ba/Ti ratio change affects the transformation from diamagnetic to ferromagnetic-like. The elements (Ba, Ti and O) chemical state is shown and its bonding to the corresponding element along with the X-ray photoelectron spectroscopy pattern of the BTX2 sample. The element of oxygen binds to Ti and Ba while Ba element exists in two chemical states.

Selective recovery of manganese from spent ternary lithium-ion batteries for efficient catalytic oxidation of VOCs: Unveiling the mechanism of activity Enhancement in recycled catalysts

With the widespread application of ternary lithium-ion batteries (TLBs) in various fields, the disposal of spent TLBs has become a globally recognized issue. This study proposes a novel method for reutilizing metal resources from TLBs. Through selective oxidation, manganese in a leaching solution of TLBs was converted into MnO2 with α, γ, and δ crystal phases (referred to as T-MnO2) for catalytic oxidation of volatile organic compounds (VOCs), while efficiently separating manganese from high-value metals such as nickel, cobalt, and lithium, achieving a manganese recovery rate of 99.99%. Compared to similar MnO2 prepared from pure materials, T-MnO2 exhibited superior degradation performance for toluene and chlorobenzene, with T90 decreasing by around 30 °C. The acidic synthesis environment provided by the leaching solution and the doping of trace metals altered the physicochemical properties of T-MnO2, such as increased specific surface area, elevated surface manganese valence, and improved redox performance and oxygen vacancy properties, enhancing its catalytic oxidation capacity. Furthermore, the degradation pathway of toluene on T-γ-MnO2 was inferred using thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) and in-situ DRIFTs. This study provides a novel approach for recycling spent TLBs and treating VOCs catalytically.

Density Functional Theory Study of Local Environment Effects on Oxygen Vacancy Properties in Magnetite

Density Functional Theory Study of Local Environment Effects on Oxygen Vacancy Properties in Magnetite

Regulating oxygen vacancies in ultrathin δ-MnO2 nanosheets with superior activity for gaseous ozone decomposition

For ozone decomposition, ultrathin δ-MnO2 nanosheets were synthesized and the properties of oxygen vacancies were regulated. The as-synthesized catalyst exhibited superior activity.

An evaluation of fluorinated titanium oxide nanocrystals with UV exposure treatment for oxygen vacancy control

Abstract The oxygen vacancy properties of densified titanium oxide (TiO2) nanocrystals (NCs) with different surface ligand states were evaluated. Fluorous ligand modification resulting in the high densification of NCs and the effect of residual ligands on the surface of the NCs using ultraviolet (UV)-exposure treatment were investigated. After synthesizing the TiO2 NCs at 80 °C, their modification proceeded using 2,2,2-trifluoroacetic acid as the fluorous ligand. NC thin films were formed using spin-casting, after which the UV-exposure treatment was performed. According to the analytical results of crystalline size, surface, optical properties, and surface ligand states of the TiO2 NCs, the ligands on the NCs were decomposed by the UV-exposure treatment under various atmospheres and the flatness of the NC thin films was found to be controlled by the fluorous ligand modification. Thus, the recombination effect of the oxygen vacancies could be controlled by the fluorous ligand modification and UV-exposure treatment.

Electronic structures and optical properties of Ce-doped anatase TiO<sub>2</sub> with oxygen vacancy

<sec> The crystal structures, defect formation energy, electronic structures and optical properties of oxygen vacancy and/or Ce-(co)doped anatase TiO<sub>2</sub> are investigated by using density functional theory plus <i>U</i> calculations. </sec><sec> The calculated results indicate that lattice distortion induces the enhanced octahedral dipole moment in Ce doped TiO<sub>2</sub> crystal when introducing oxygen vacancy into the lattice of the TiO<sub>2</sub> crystal, which is effective for separating the photo-excited electron-hole pairs; meanwhile, compared with the valence band of pure TiO<sub>2</sub> and TiO<sub>2</sub> mono-doped separately with Ce and oxygen vacancy, the valence band of TiO<sub>2</sub> co-doped with Ce and oxygen vacancy broadens drastically, which is mainly contributed from the electronic states of Ce 5d, Ti 4s and O 2p in the valence band shifting toward the lower energy direction. As a result, Ce doped TiO<sub>2</sub> with oxygen vacancy is beneficial to the mobility of photo-generated carriers in TiO<sub>2</sub>. Similarly, the anti-bonding states also move toward the lower band energy direction, which are formed by the mixture of Ce 4f, Ce 5d, Ti 3d, and O 2p orbits in the conduction band. Due to these shifts, the energy gap of Ce and oxygen vacancy codoped TiO<sub>2</sub> is narrowed to 2.67 eV with the emerge of the occupied impurity energy levels near Fermi level. Because of the above-mentioned excellence features, the absorption spectra for doped systems exhibit remarkable red-shift, especially, the intensity of optical absorption of TiO<sub>2</sub> co-doped with Ce and oxygen vacancy in the visible region and the infra-red region are obviously stronger than those of the Ce mono-doped TiO<sub>2</sub>. </sec><sec> When introducing oxygen vacancy into the Ce-doped system, the calculated conduction band energy edge position changes from −0.27 eV to −0.32 eV, which implies that the reducing power of the conduction band edge of TiO<sub>2</sub> is remarkably enhanced. More fascinatingly, the calculated band energy edges for the Ce and oxygen vacancy codoped TiO<sub>2</sub> can satisfy the basic requirement for water splitting under visible light irradiation.</sec><sec> In conclusion, Ce and oxygen vacancy co-doped system can effectively strengthen the photo-catalytic activity of TiO<sub>2</sub> and improve the utilization of the solar light; and our calculated results provide a powerful theoretical basis for the applications of the Ce and oxygen vacancy co-doped anatase TiO<sub>2</sub> in visible-light-driven water splitting in the future research. </sec>

(Invited) The Effect of (La,Sr)MnO3 Cathode Surface Termination on Its Electronic Structure

La1-xSrxMnO3 (LSM) was one of the first perovskites employed as SOFC cathode material and is still used in the form of porous composites with the respective electrolyte [1]. In our previous study [2], we analyzed oxygen adsorption, dissociation and migration on the (001) MnO2-terminated LM surface. In pure LaMnO3, the MnO2 (001) termination was found to be the energetically most stable, however with an increase of Sr doping, the (La,Sr)O termination is predicted to become even more favorable thermodynamically [3]. In this talk, we discuss and compare the results of first principles calculations on the elementary steps (oxygen vacancy formation, O2 molecule and O atom adsorption) of the oxygen reduction reaction on (La,Sr)MnO3 on the two (001) polar terminations – (La,Sr)O and MnO2. The LSM slab calculations were performed using the plane wave VASP computer code with GGA exchange correlation functionals. Properties of oxygen vacancies in different planes from the surface were analyzed. The vacancy formation energy on the MnO2 terminated surface is smaller than that in bulk. In contrast, the vacancy energy on the (La,Sr)O termination is larger, thus strongly reducing the surface vacancy concentration. Our approach allows for a clear separation of the two distinct effects -- different surface terminations and slab cation stoichiometry (ratio of a number of (La,Sr) ions to Mn that affects the average Mn oxidation state). It is found that oxygen vacancy formation energy in the bulk (slab center) is almost independent of the Mn oxidation state in the region +2.6 to +3.25, whereas it is monotonically decreasing on both surfaces. This surface-to-bulk discrepancy will be discussed. The oxygen atom adsorption energy on the (La,Sr)O termination considerably exceeds that on the MnO2 termination. As a result, the equilibrium oxygen adsorbate concentration was found to be about two orders of magnitude larger for the (La,Sr)O termination, but on the other hand, the surface oxygen vacancy concentration is smaller by nearly six orders of magnitude. Therefore, the oxygen reduction rate on (La,Sr)O termination is expected to be significantly lower than on the MnO2 termination. [1]. M. Kuklja, E.A. Kotomin, R. Merkle, Yu.A. Mastrikov, J. Maier, PCCP 15, 5443 (2013). [2]. Yu.A. Mastrikov, R. Merkle, E. Heifets, E. A. Kotomin, J. Maier, J. Phys. Chem. C 114, 3017 (2010). [3]. S. Piskunov, E. Heifets, T. Jacob, E. A. Kotomin, E. Spohr, Phys. Rev.B 78, 121406 (2008).

P055 第一原理解析に基づくPbTiO_3酸素空孔のひずみ誘起磁気特性(メカボケーション学生研究発表セッション)

P055 第一原理解析に基づくPbTiO_3酸素空孔のひずみ誘起磁気特性(メカボケーション学生研究発表セッション)

Au doping effects in HfO2-based resistive switching memory

In this paper, first principles calculation is performed to investigate the impact of Au doping on the properties of oxygen vacancy in HfO2, including defect energy level and formation energy (Ef). The Ef is significantly reduced in Au-doped HfO2 film. In the experiments, the Cu/HfO2: Au/Pt memory devices are fabricated and exhibit high resistance ratio, reliable date retention and good endurance. This performance improvement is clarified to the suppressed randomicity of oxygen vacancy filaments’ formation by trivalent Au-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.

Epitaxial Cubic Ce2O3 Films via Ce-CeO2 Interfacial Reaction.

Thin films of reduced ceria supported on metals are often applied as substrates in model studies of the chemical reactivity of ceria based catalysts. Of special interest are the properties of oxygen vacancies in ceria. However, thin films of ceria prepared by established methods become increasingly disordered as the concentration of vacancies increases. Here, we propose an alternative method for preparing ordered reduced ceria films based on the physical vapor deposition and interfacial reaction of Ce with CeO2 films. The method yields bulk-truncated layers of cubic c-Ce2O3. Compared to CeO2 these layers contain 25% of perfectly ordered vacancies in the surface and subsurface allowing well-defined measurements of the properties of ceria in the limit of extreme reduction. Experimentally, c-Ce2O3(111) layers are easily identified by a characteristic 4 × 4 surface reconstruction with respect to CeO2(111). In addition, c-Ce2O3 layers represent an experimental realization of a normally unstable polymorph of Ce2O3. During interfacial reaction, c-Ce2O3 nucleates on the interface between CeO2 buffer and Ce overlayer and is further stabilized most likely by the tetragonal distortion of the ceria layers on Cu. The characteristic kinetics of the metal-oxide interfacial reactions may represent a vehicle for making other metastable oxide structures experimentally available.

The electronic properties of the interface structure between ZnO and amorphous HfO2

Abstract We investigate the atomic structure of the interface between crystalline ZnO and amorphous HfO2 (a-HfO2) and the electronic properties of oxygen vacancy (VO) near the interface through first-principles density-functional calculations. From the band alignment of ZnO/a-HfO2 interfaces, the conduction band offset is estimated to be 2.14–2.39 eV, while the potential barrier for hole conduction is nearly zero. The defect level of VO is higher in gate oxide than in ZnO. As VO behaves as a charge trap center in gate oxide, this defect can cause threshold voltage instability, while it does not in the ZnO region.

Oxygen Vacancies in Amorphous HfO2 and SiO2

ABSTRACTFormation energies and electronic properties of oxygen vacancies in amorphous HfO2 gate dielectrics are investigated by employing the first-principles method based on the density functional theory. We have found that the formation energy of neutral oxygen vacancy in amorphous HfO2 distributes from 4.7 to 6.1 eV, most of which is lower than the value for cubic HfO2, 6.0 eV. We also investigated the stabilities of the Vo pairs in various charged state and compared with those in amorphous SiO2. We found that Vo++ is stabilized in the vicinity of Vo in SiO2. In HfO2, however, this does not happen. This suggests the difference of defect propagation mechanism in HfO2 and SiO2.

Modeling of the structure and properties of oxygen vacancies in amorphous silica

We used an embedded cluster method to predict and characterize possible structural types of neutral and positively charged oxygen vacancies in amorphous silica. Defects were treated at 70 different oxygen sites of continuous random network amorphous structure generated using classical molecular dynamics. The neutral vacancies are characterized by a wide distribution of formation energies and structural parameters. Our modeling predicts the two major structural types of positively charged vacancies (${E}^{\ensuremath{'}}$ centers): dimer and dangling bond centers. The local structure of both types of centers depends on the medium range structure of the surrounding amorphous network. The majority of the dangling bond centers are unpuckered. We used structural ``fingerprints'' derived from similar calculations of oxygen vacancy type centers in quartz and from experiment to find two other structural types of dangling bond centers: the puckered configuration and the back-projected configuration of ${E}^{\ensuremath{'}}$ centers. In each case we find a distribution of both structural and EPR parameters. However, the average values of the EPR parameters for all dangling bond configurations are very similar. The structural criteria which favor the formation of different types of centers in the original amorphous structure are formulated in terms of the average Si-O distance of oxygen ion with its two neighboring silicon ions.

Role of oxygen vacancy defect states in the n-type conduction of β-Ga2O3

Based on semiempirical quantum-chemical calculations, the electronic band structure of β-Ga2O3 is presented and the formation and properties of oxygen vacancies are analyzed. The equilibrium geometries and formation energies of neutral and doubly ionized vacancies were calculated. Using the calculated donor level positions of the vacancies, the high temperature n-type conduction is explained. The vacancy concentration is obtained by fitting to the experimental resistivity and electron mobility.

Electronic properties of oxygen vacancies in La2CuO4-y.

The electronic properties of oxygen vacancies in chemically pure ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$ have been investigated by the ab initio pseudofunction method using a supercell geometry. Oxygen vacancies alter the electronic structure significantly, breaking up the 2-eV-wide partially filled conduction band into narrower bands, which are only about 0.1 eV wide in ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{3.75}$. Our results suggest that vacancy-induced narrow bands near the Fermi level could lead to the antiferromagnetic state observed in some nonstoichiometric ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$ samples.