scholarly journals Influence of Mixed Valence on the Formation of Oxygen Vacancy in Cerium Oxides

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4041 ◽  
Author(s):  
Gege Zhou ◽  
Wentong Geng ◽  
Lu Sun ◽  
Xue Wang ◽  
Wei Xiao ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Valence State ◽  
Density Functional ◽  
Formation Energy ◽  
Oxygen Vacancies ◽  
Mixed Valence ◽  
Oxygen Storage ◽  
Electronic Charge ◽  
Covalent Bonds ◽  
Cerium Oxides

Ceria is one of the most important functional rare-earth oxides with wide industrial applications. Its amazing oxygen storage/release capacity is attributed to cerium’s flexible valence conversion between 4+ and 3+. However, there still exists some debate on whether the valence conversion is due to the Ce-4f electron localization-delocalization transition or the character of Ce–O covalent bonds. In this work, a mixed valence model was established and the formation energies of oxygen vacancies and electronic charges were obtained by density functional theory calculations. Our results show that the formation energy of oxygen vacancy is affected by the valence state of its neighboring Ce atom and two oxygen vacancies around a Ce4+ in CeO2 have a similar effect to a Ce3+. The electronic charge difference between Ce3+ and Ce4+ is only about 0.4e. Therefore, we argue that the valence conversion should be understood according to the adjustment of the ratio of covalent bond to ionic bond. We propose that the formation energy of oxygen vacancy be used as a descriptor to determine the valence state of Ce in cerium oxides.

scholarly journals Ab-Initio Calculations of Oxygen Vacancy in Ga2O3 Crystals

2021 ◽  
Vol 58 (2) ◽  
pp. 3-10
Author(s):  
A. Usseinov ◽  
Zh. Koishybayeva ◽  
A. Platonenko ◽  
A. Akilbekov ◽  
J. Purans ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Gallium Oxide ◽  
Formation Energy ◽  
Oxygen Vacancies ◽  
Wide Band ◽  
Electronic Charge ◽  
Charge Redistribution ◽  
Wide Band Gap ◽  
Exchange Correlation ◽  
Deep Donor

Abstract Gallium oxide β-Ga2O3 is an important wide-band gap semiconductor. In this study, we have calculated the formation energy and transition levels of oxygen vacancies in β-Ga2O3 crystal using the B3LYP hybrid exchange-correlation functional within the LCAO-DFT approach. The obtained electronic charge redistribution in perfect Ga2O3 shows notable covalency of the Ga-O bonds. The formation of the neutral oxygen vacancy in β-Ga2O3 leads to the presence of deep donor defects with quite low concentration. This is a clear reason why oxygen vacancies can be hardly responsible for n-type conductivity in β-Ga2O3.

scholarly journals On the Effects of Doping on the Catalytic Performance of (La,Sr)CoO3. A DFT Study of CO Oxidation

Catalysts ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 312 ◽  
Author(s):  
Antonella Glisenti ◽  
Andrea Vittadini
Keyword(s):  
Catalytic Activity ◽  
Co Oxidation ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Formation Energy ◽  
Oxygen Vacancies ◽  
Catalytic Performance ◽  
Energy Profiles ◽  
High Concentrations ◽  
3D Impurities

The effects of modifying the composition of LaCoO3 on the catalytic activity are predicted by density functional calculations. Partially replacing La by Sr ions has benefical effects, causing a lowering of the formation energy of O vacancies. In contrast to that, doping at the Co site is less effective, as only 3d impurities heavier than Co are able to stabilize vacancies at high concentrations. The comparison of the energy profiles for CO oxidation of undoped and of Ni-, Cu-m and Zn-doped (La,Sr)CoO3(100) surface shows that Cu is most effective. However, the effects are less spectacular than in the SrTiO3 case, due to the different energetics for the formation of oxygen vacancies in the two hosts.

Oxygen vacancy migration in CSZ using density functional theory

2008 ◽  
Vol 1122 ◽  
Author(s):  
Byeong-Eon Lee ◽  
Dae-Hee Kim ◽  
Yeong-Cheol Kim
Keyword(s):  
Density Functional Theory ◽  
Oxygen Vacancy ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Nearest Neighbor ◽  
Functional Theory ◽  
The Third ◽  
Vacancy Migration ◽  
Neighbor Site ◽  
Formation Energies

AbstractWe studied oxygen migration in calcia-stabilized cubic zirconia (CSZ) using density functional theory. A Ca atom was substituted for a Zr atom in a 2×2×2 ZrO2 cubic supercell, and an oxygen vacancy was produced to satisfy the charge neutrality condition. We found that the formation energies of an oxygen vacancy, as a function of its location with respect to the Ca atom, were varied. The relative formation energies of the oxygen vacancies located at the first-, second-, third-, and fourth-nearest-neighbors were 0.0, −0.07, 0.19, and 0.19 eV, respectively. Therefore, the oxygen vacancy located at the second-nearest-neighbor site of the Ca atom was the most favorable, the oxygen vacancy located at the first-nearest-neighbor site was the second most favorable, and the oxygen vacancies at the third- and fourth-nearest-neighbor sites were the least favorable. We also calculated the energy barriers for the oxygen vacancy migration between oxygen sites. The energy barriers between the first and the second nearest sites, the second and third nearest sites, and the third and fourth nearest sites were 0.11, 0.46, and 0.23 eV, respectively. Therefore, the oxygen vacancies favored the first- and second-nearest-neighbor oxygen sites when they drifted under an electric field.

Structural and Electronic Properties of Oxygen Vacancies in Monoclinic HfO2

2007 ◽  
Vol 996 ◽  
Author(s):  
Peter Broqvist ◽  
Alfredo Pasquarello
Keyword(s):  
Oxygen Vacancy ◽  
Optical Absorption ◽  
Total Energy ◽  
Band Gap ◽  
Electronic Properties ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Structural And Electronic Properties ◽  
Defect Levels ◽  
Hybrid Density Functional

AbstractWe study structural and electronic properties of the oxygen vacancy in monoclinic HfO2 for five different charge states. We use a hybrid density functional to accurately reproduce the experimental band gap. To compare with measured defect levels, we determine total-energy differences appropriate to the considered experiments. Our results show that the oxygen vacancy can consistently account for the defect levels observed in optical absorption, direct electron injection, and trap-assisted conduction experiments.

Ab Initio Studies of Nb Doping Effect on the Formation and Diffusion of Oxygen Vacancy and Ti Interstitial in Rutile TiO2

2011 ◽  
Vol 304 ◽  
pp. 142-147 ◽  
Author(s):  
Xu Wang ◽  
Fu He Wang
Keyword(s):  
Activation Energy ◽  
Oxygen Vacancy ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Formation Energy ◽  
Suppressive Effect ◽  
Nb Doping ◽  
O Vacancy ◽  
And Migration ◽  
And Diffusion

The effect of Nb doping on the formation and diffusion of O vacancies and interstitial Ti in rutile TiO2 are studied by the use of ab initio density-functional calculations. Our calculation showed that the activation energy for the diffusion of O vacancy with Nb doping is higher than that of pure. That owing to suppressive effect of Nb doping on the formation of O vacancy. Different from the effect of Nb doping on O vacancy, both of the formation energy and migration barrier of interstitial Ti increase with the Nb doping. Our calculated results may be one of the reasons why Nb doping can improve oxidation resistance of γ-TiAl.

Formation of oxygen vacancies in Li2FeSiO4: first-principles calculations

2021 ◽  
Vol 23 (36) ◽  
pp. 20444-20452
Author(s):  
Lihong Zhang ◽  
Shunqing Wu ◽  
Jianwei Shuai ◽  
Zhufeng Hou ◽  
Zizhong Zhu
Keyword(s):  
Oxygen Vacancy ◽  
First Principles ◽  
Formation Energy ◽  
Oxygen Vacancies ◽  
Vacancy Formation Energy ◽  
Vacancy Formation ◽  
First Principles Calculations ◽  
Temperature And Pressure

The oxygen vacancy (left panel) and the vacancy formation energy as a function of temperature and pressure (right panel).

scholarly journals Introducing Oxygen Vacancies in Li4Ti5O12 via Hydrogen Reduction for High-Power Lithium-Ion Batteries

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1655
Author(s):  
Yiguang Zhou ◽  
Shuhao Xiao ◽  
Zhenzhe Li ◽  
Xinyan Li ◽  
Jintao Liu ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Lithium Ion Batteries ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Electronic Conductivity ◽  
Lithium Ion ◽  
High Rate ◽  
Oxygen Vacancy Concentration ◽  
Rate Performance ◽  
High Rate Performance

Li4Ti5O12 (LTO), known as a zero-strain material, is widely studied as the anode material for lithium-ion batteries owing to its high safety and long cycling stability. However, its low electronic conductivity and Li diffusion coefficient significantly deteriorate its high-rate performance. In this work, we proposed a facile approach to introduce oxygen vacancies into the commercialized LTO via thermal treatment under Ar/H2 (5%). The oxygen vacancy-containing LTO demonstrates much better performance than the sample before H2 treatment, especially at high current rates. Density functional theory calculation results suggest that increasing oxygen vacancy concentration could enhance the electronic conductivity and lower the diffusion barrier of Li+, giving rise to a fast electrochemical kinetic process and thus improved high-rate performance.

scholarly journals A quantum-mechanical investigation of oxygen vacancies and copper doping in the orthorhombic CaSnO3 perovskite

2018 ◽  
Vol 20 (32) ◽  
pp. 20970-20980 ◽  
Author(s):  
Jefferson Maul ◽  
Iêda Maria Garcia dos Santos ◽  
Julio Ricardo Sambrano ◽  
Silvia Casassa ◽  
Alessandro Erba
Keyword(s):  
Density Functional Theory ◽  
Oxygen Vacancy ◽  
Electronic Properties ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Quantum Mechanical ◽  
Functional Theory ◽  
Copper Doping ◽  
Oxygen Vacancy Formation ◽  
Mechanical Investigation

In this study we explore the implications of oxygen vacancy formation and of copper doping in the orthorhombic CaSnO3 perovskite, by means of density functional theory, focusing on energetic and electronic properties.

Effects of halogen substituted on the Mn-O electron transfer of NiMn2O4

2019 ◽  
Vol 33 (10) ◽  
pp. 1950090
Author(s):  
Hai-Long Li ◽  
Liang Bian ◽  
Fa-Qin Dong ◽  
Wei-Min Li ◽  
Hao Zou ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Oxygen Vacancy ◽  
Theoretical Basis ◽  
Density Functional ◽  
Mixed Valence ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Hybrid Orbital ◽  
Hybrid Orbitals ◽  
Valence Configuration

To observe the effect of halogen-substitution on the Mn-O electron transfer of NiMn2O4, we calculated Mn-mixed-valence configuration (charge-disproportionation) and oxygen vacancy by the density functional theory (DFT). The results indicate that the halogen-p5 state induces the O-2p orbital splitting to create an oxygen vacancy in the VB (valence band: about −5 eV). The oxygen vacancy can capture an electron from Mn[Formula: see text]-3d5 orbital that makes the Mn[Formula: see text]-3d5 change to Mn[Formula: see text]-3d4 states (Mn-charge disproportionate), and providing many effective-hole (40.14 [Formula: see text] 96.72 × 10[Formula: see text] kg). The halogen-p5-O-2p4 hybrid orbitals enhance the O-2p4-Mn-3d5 p-d hybrid orbital (about 19.18 electron). That increases the surface potential in Mn-O octahedron (for Cl-substituted: about 60 meV), the corresponding electron–electron interactions change from complex t[Formula: see text] (O-2p4-Mn[Formula: see text]-3d[Formula: see text] to complete [Formula: see text] (O-2p4-Mn[Formula: see text]-3d[Formula: see text]-e[Formula: see text](O-2p4-halogen-p5) orbital. This study effectively analyzes the microscopic changes of the electron transfer caused by the small amount of doping, provides a theoretical basis for the design of NMO-based semiconductor material.

scholarly journals Mechanisms of Visible Light Photocatalysis in N-Doped Anatase TiO2with Oxygen Vacancies from GGA+U Calculations

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Hsuan-Chung Wu ◽  
Yu-Siang Lin ◽  
Syuan-Wei Lin
Keyword(s):  
Visible Light ◽  
Band Gap ◽  
Density Functional ◽  
Nitrogen Doping ◽  
Formation Energy ◽  
Oxygen Vacancies ◽  
Energy Charge ◽  
Visible Light Photocatalysis ◽  
Donor States ◽  
Band Gap Narrowing

We have systematically studied the photocatalytic mechanisms of nitrogen doping in anatase TiO2using first-principles calculations based on density functional theory, employing HubbardU(8.47 eV) on-site correction. The impurity formation energy, charge density, and electronic structure properties of TiO2supercells containing substitutional nitrogen, interstitial nitrogen, or oxygen vacancies were evaluated to clarify the mechanisms under visible light. According to the formation energy, a substitutional N atom is better formed than an interstitial N atom, and the formation of an oxygen vacancy in N-doped TiO2is easier than that in pure TiO2. The calculated results have shown that a significant band gap narrowing may only occur in heavy nitrogen doping. With light nitrogen doping, the photocatalysis under visible light relies on N-isolated impurity states. Oxygen vacancies existence in N-doped TiO2can improve the photocatalysis in visible light because of a band gap narrowing and n-type donor states. These findings provide a reasonable explanation of the mechanisms of visible light photocatalysis in N-doped TiO2.

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