Screened Coulomb interactions of localized electrons in transition metals and transition-metal oxides

2012 ◽  
Vol 86 (16) ◽  
Author(s):  
Bi-Ching Shih ◽  
Tesfaye A. Abtew ◽  
Xun Yuan ◽  
Wenqing Zhang ◽  
Peihong Zhang
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Coulomb Interactions ◽  
Localized Electrons

Transition Metal Oxide-Diamond Interfaces for Electron Emission Applications

2013 ◽  
Vol 740-742 ◽  
pp. 761-764
Author(s):  
Amit K. Tiwari ◽  
Jonathan P. Goss ◽  
Patrick R. Briddon ◽  
Nicholas G. Wright ◽  
Alton B. Horsfall ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Oxides ◽  
Electron Affinity ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Chemical Species ◽  
Negative Electron Affinity ◽  
Diamond Surfaces ◽  
Electron Emitters

Diamond surfaces with suitable adsorbed chemical species can exhibit both negative and positive electron affinities, arising from the complex electrostatic interplay between adsorbates and surface carbon atoms of diamond lattice. We presents the results of density functional calculations into the energetics and the electron affinity of diamond (100) surfaces terminated with the oxides of selected transition metals. We find that for a correct stoichiometry, oxides of transition metals, such as Ti and Zn, exhibit a large negative electron affinity of around 3 eV. The desorption of transition metal oxides is found to be highly endothermic. We therefore propose that transition metal oxides are promising for the surface coating of diamond-based electron emitters, as these exhibit higher thermal stability in comparison to the commonly used CsO terminations, while retaining the advantage of inducing a large negative electron affinity.

scholarly journals Electrochemical properties and structural evolution of O3-type layered sodium mixed transition metal oxides with trivalent nickel

2017 ◽  
Vol 5 (9) ◽  
pp. 4596-4606 ◽  
Author(s):  
Plousia Vassilaras ◽  
Deok-Hwang Kwon ◽  
Stephen T. Dacek ◽  
Tan Shi ◽  
Dong-Hwa Seo ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Oxides ◽  
Electrochemical Properties ◽  
Transition Metal Oxides ◽  
Structural Evolution ◽  
Redox Behavior ◽  
Layered Oxides ◽  
Mixed Transition

We demonstrate how to control the structural evolution and associated redox behavior in Na layered oxides by mixing trivalent Ni with other transition metals.

Heavy fermions in transition metals and transition-metal oxides

2003 ◽  
Vol 34 (4) ◽  
pp. 399-407 ◽  
Author(s):  
H.-A. Krug von Nidda ◽  
R. Bulla ◽  
N. B�ttgen ◽  
M. Heinrich ◽  
A. Loidl
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Heavy Fermions

scholarly journals Stable Surfaces that Bind too Tightly: Can Range Separated Hybrids or DFT+U Improve Paradoxical Descriptions of Surface Chemistry?

2019 ◽  
Author(s):  
Qing Zhao ◽  
Heather Kulik
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Local Density ◽  
Computational Cost ◽  
Hartree Fock ◽  
Hybrid Functionals ◽  
Local Range

Approximate, semi-local density functional theory (DFT) suffers from delocalization error that can lead to a paradoxical overbinding of surface adsorbates and overestimation of surface stabilities in catalysis modeling. We investigate the effect of two widely applied approaches for delocalization error correction, i) affordable DFT+U (i.e., semi-local DFT augmented with a Hubbard U) and ii) hybrid functionals with an admixture of Hartree-Fock (HF) exchange, on surface and adsorbate energies across a range of rutile transition metal oxides widely studied for their promise as water splitting catalysts. We observe strongly row- and period-dependent trends with DFT+U, which increases surface formation energies only in early transition metals (e.g., Ti, V) and decreases adsorbate energies only in later transition metals (e.g., Ir, Pt). Both global and local hybrids destabilize surfaces and reduce adsorbate binding across the periodic table, in agreement with higher-level reference calculations. Density analysis reveals why hybrid functionals correct both quantities, whereas DFT+U does not. We recommend local, range-separated hybrids for the accurate modeling of catalysis in transition metal oxides at only a modest increase in computational cost over semi-local DFT.

scholarly journals Stable Surfaces that Bind too Tightly: Can Range Separated Hybrids or DFT+U Improve Paradoxical Descriptions of Surface Chemistry?

2019 ◽  
Author(s):  
Qing Zhao ◽  
Heather Kulik
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Local Density ◽  
Computational Cost ◽  
Hartree Fock ◽  
Hybrid Functionals ◽  
Local Range

Approximate, semi-local density functional theory (DFT) suffers from delocalization error that can lead to a paradoxical overbinding of surface adsorbates and overestimation of surface stabilities in catalysis modeling. We investigate the effect of two widely applied approaches for delocalization error correction, i) affordable DFT+U (i.e., semi-local DFT augmented with a Hubbard U) and ii) hybrid functionals with an admixture of Hartree-Fock (HF) exchange, on surface and adsorbate energies across a range of rutile transition metal oxides widely studied for their promise as water splitting catalysts. We observe strongly row- and period-dependent trends with DFT+U, which increases surface formation energies only in early transition metals (e.g., Ti, V) and decreases adsorbate energies only in later transition metals (e.g., Ir, Pt). Both global and local hybrids destabilize surfaces and reduce adsorbate binding across the periodic table, in agreement with higher-level reference calculations. Density analysis reveals why hybrid functionals correct both quantities, whereas DFT+U does not. We recommend local, range-separated hybrids for the accurate modeling of catalysis in transition metal oxides at only a modest increase in computational cost over semi-local DFT.

HREM Study of electron-induced surface radiation damage in ReO3

1991 ◽  
Vol 49 ◽  
pp. 636-637
Author(s):  
R. Ai ◽  
H.-J. Fan ◽  
L. D. Marks
Keyword(s):  
Transition Metal ◽  
Metal Ions ◽  
Metal Oxides ◽  
Electron Irradiation ◽  
Transition Metal Oxides ◽  
Carbon Film ◽  
Transition Metal Ions ◽  
Surface Radiation ◽  
Valence Transition ◽  
Electron Microscopes

It has been known for a long time that electron irradiation induces damage in maximal valence transition metal oxides such as TiO2, V2O5, and WO3, of which transition metal ions have an empty d-shell. This type of damage is excited by electronic transition and can be explained by the Knoteck-Feibelman mechanism (K-F mechanism). Although the K-F mechanism predicts that no damage should occur in transition metal oxides of which the transition metal ions have a partially filled d-shell, namely submaximal valence transition metal oxides, our recent study on ReO3 shows that submaximal valence transition metal oxides undergo damage during electron irradiation.ReO3 has a nearly cubic structure and contains a single unit in its cell: a = 3.73 Å, and α = 89°34'. TEM specimens were prepared by depositing dry powders onto a holey carbon film supported on a copper grid. Specimens were examined in Hitachi H-9000 and UHV H-9000 electron microscopes both operated at 300 keV accelerating voltage. The electron beam flux was maintained at about 10 A/cm2 during the observation.

Problems with oxygen analysis in the system MgO-Al2O3-SiO2 with the electron microprobe

1992 ◽  
Vol 50 (2) ◽  
pp. 1624-1625
Author(s):  
Michel Fialin ◽  
Guy Rémond
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Electrostatic Charge ◽  
Carbon Layer ◽  
Sample Holder ◽  
Rock Matrix ◽  
Electrical Discharges ◽  
Thin Carbon ◽  
Beam Instabilities

Oxygen-bearing minerals are generally strong insulators (e.g. silicates), or if not (e.g. transition metal oxides), they are included within a rock matrix which electrically isolates them from the sample holder contacts. In this respect, a thin carbon layer (150 Å in our laboratory) is evaporated on the sections in order to restore the conductivity. For silicates, overestimated oxygen concentrations are usually noted when transition metal oxides are used as standards. These trends corroborate the results of Bastin and Heijligers on MgO, Al2O3 and SiO2. According to our experiments, these errors are independent of the accelerating voltage used (fig.l).Owing to the low density of preexisting defects within the Al2O3 single-crystal, no significant charge buildup occurs under irradiation at low accelerating voltage (< 10keV). As a consequence, neither beam instabilities, due to electrical discharges within the excited volume, nor losses of energy for beam electrons before striking the sample, due to the presence of the electrostatic charge-induced potential, are noted : measurements from both coated and uncoated samples give comparable results which demonstrates that the carbon coating is not the cause of the observed errors.

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