Electronic structure of face-centred cubic MoO2: A comparative study by the full potential linearized augmented plane wave method, X-ray emission spectroscopy and X-ray photoelectron spectroscopy (original) (raw)
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XES, XPS and NEXAFS studies of the electronic structure of cubic MoO1.9 and H1.63MoO3 thick films
Journal of Alloys and Compounds, 2004
X-ray emission spectroscopy (XES), X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) methods were used to study the electronic structure of cubic MoO 1.9 and H 1.63 MoO 3 thick films. For comparison, the orthorhombic form of molybdenum trioxide, MoO 3 , was also studied. XP valence-band and Mo 3d and O 1s core-level spectra, O K␣ emission bands and NEXAFS O 1s spectra were measured. Half-widths of both the XP valence-bands and O K␣ emission bands decreases in the sequence cubic H 1.63 MoO 3 → orthorhombic MoO 3 → cubic MoO 1.9 . The XPS and NEXAFS data reveal that the charge states of oxygen atoms do not change in the above sequence of compounds. The formation of an additional near-Fermi sub-band is characteristic for the XP valence-band spectra of cubic MoO 1.9 and H 1.63 MoO 3 . The XES measurements indicate that the energy positions of maxima and of the centers of gravity of the O K␣ bands remain constant within accuracy of the experiment for all the compounds studied.
Hard X-ray photoemission spectroscopy of pyrochlore molybdenum oxides R2Mo2O7 (R=Sm, Tb)
Physica B: Condensed Matter, 2006
We have carried out hard X-ray photoemission spectroscopy (HXPES) for pyrochlore molybdenum oxides Sm 2 Mo 2 O 7 and Tb 2 Mo 2 O 7 single crystals with excitation energy of 5.95 keV, in order to investigate electronic structures and correlations in the bulk. The Mo 3d core spectra show complex features, in contrast to an ordinary doublet spectral feature derived from the spin-orbit interaction, indicating significant electron correlation in the valence band. While an intense peak structure at $0.5 eV is observed in the valence band of Sm 2 Mo 2 O 7 , the peak is broadened and shifted way in Tb 2 Mo 2 O 7 , which suggests the difference of the electron correlation energy depending on the rare-earth site. r
Physical Review B, 2009
A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the new full-potential augmented spherical wave (ASW) method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional hole-like surfaces centered around the Z-and B-point could be resolved; these surfaces were an artefact of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighbouring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2, which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.
Surface Science, 2001
Ab initio density functional theory cluster studies on the MoO 3 (0 1 0) surface as well as ultraviolet photoemission (UPS) experiments on well-crystallized single phase Mo oxides are carried out to examine the electronic structure of the oxide systems. In addition, electronic details of dierent surface oxygen vacancies are studied by appropriate vacancy clusters. Calculations on embedded clusters as large as Mo 15 O 56 H 22 con®rm the mixed covalent/ionic character of the oxide. The computed width of the O 2sp dominated valence band region of MoO 3 , about 7 eV, agrees well with the present photoemission data for MoO 3 (0 1 0) samples. The overall shape of the computed densities of states (DOS) in the O 2sp region of MoO 3 is rather similar to the measured UPS intensity curves indicating weak energy dependence of corresponding transition matrix elements. Calculated vacancy energies for the dierent surface oxygen sites at MoO 3 (0 1 0) yield rather large values, 6.8±7.6 eV, which shows that oxygen is bound quite strongly to the substrate. Vacancy formation leads to reduction of neighboring molybdenum centers which expresses itself by increased metal d electron occupation and corresponding DOS contributions above the O 2sp region. This is consistent with the experimental UPS data for MoO 3 (0 1 0) where oxygen vacancies have been introduced by mild ion bombardment. It is further supported by the present UPS data for well-crystallized intermediate molybdenum oxides, such as Mo 18 O 52 , Mo 8 O 23 , or Mo 4 O 11 . These oxides show, depending on the degree of reduction, one or two additional peaks above the valence band. Characteristic changes in the intensity ratios of the O 2sp peaks can be interpreted on the basis of the theoretical DOS results as a preferential loss of bridging oxygen from the MoO 3 lattice. Mild ion bombardment, a technique which is often used to clean surfaces in UHV experiments, results in the case of MoO 3 (0 1 0) in considerable surface reduction. The reduced Mo species is comparable to that in MoO 2 as indicated by the UP spectra. Therefore, mild ion bombardment cannot be considered a suitable tool for the preparation of molybdenum oxide surfaces. Ó
Electronic Properties of the Active Sites Present at the (011) Surface of MoO2
Adsorption Science & Technology, 2007
The DFT method was used to describe the electronic structure of the catalytically interesting (011) surface of molybdenum dioxide, with attention being particularly focused on the properties of the active sites, both molybdenum and oxygen, present at this surface. In addition, a comparison of (011)MoO2 and (100)MoO3 surfaces was undertaken since both surfaces contain not only differently coordinated oxygen sites but also the bare molybdenum centres. The electronic structures of both surfaces were obtained using the cluster method and DFT approach. The local properties of the different surface sites exposed at the (011)MoO2 surface, viz. five- and six-fold coordinated Mo atoms and nucleophilic O sites with different coordination numbers, have been discussed using charge densities, bond-order indices and molecular orbital diagrams.
Electronic Properties of the Active Sites Present at the (011) Surface of MoO 2
Adsorpt Sci Technol, 2007
The DFT method was used to describe the electronic structure of the catalytically interesting (011) surface of molybdenum dioxide, with attention being particularly focused on the properties of the active sites, both molybdenum and oxygen, present at this surface. In addition, a comparison of (011)MoO 2 and (100)MoO 3 surfaces was undertaken since both surfaces contain not only differently coordinated oxygen sites but also the bare molybdenum centres. The electronic structures of both surfaces were obtained using the cluster method and DFT approach. The local properties of the different surface sites exposed at the (011)MoO 2 surface, viz. five-and six-fold coordinated Mo atoms and nucleophilic O sites with different coordination numbers, have been discussed using charge densities, bond-order indices and molecular orbital diagrams. * The program package StoBe is a modified version of the DFT-LCGTO program package DeMon, originally developed by A. St.-Amant and D. Salahub (University of Montreal), with extensions by L.
Valence band of molybdenum by photoelectron spectroscopy
Czechoslovak Journal of Physics, 1981
Experimental photoelectron spectra of a clean polycrystalline Mo surface excited by monochrornatized A1 Ky X-rays are presented. The spectra are compared with valence bands obtained by UPS and by band structure calculations within the 5 eV region below the Mo Fermi level. Ail results mentioned above display peaks at 0.3, 1.7, 2.8 and 4 eV below E F. The energy distribution of the valence band does not vary with photon energy and electron emission angle for the four different polycrystalline Mo surfaces compared. It is concluded that the four peaks representing the Mo valence band are predominantly of bulk origin.
Band structure and related properties of molybdenum
Physical review. B, Condensed matter, 1989
Self-consistent, all-electron, local-density calculations are reported for bcc molybdenum, using the linear combination of Gaussian orbitals (LCGO) method. We obtain the density of states, the Fermi surface, charge form factors, the Cornpton profile, and the optical conductivity. Results are compared with other calculations and with experiments where these exist. A possible ferromagnetic state is found for an increased lattice constant, developing at about 8.07 a.u.
Physics Access, 2021
The structural properties of undoped and Fluorine doped Hexagonal Molybdenum dioxide (MoO2) with different doping concentrations have been calculated using Density Functional Theory (DFT) within Generalized Gradient Approximation (GGA) as implemented in Quantum Espresso (QE). The calculated results were for the formation energy of 4.17%, 8.33%, 12.5%, of F doped MoO2 are 232.5eV, 463.0eV, and 698.5eV respectively, which show the variation of energy based on the increase in the doping concentration that led to having the breakage of bond in the structure of the compound. The undoped and 4.17% of F doped MoO2 have three free atoms, which maintain the stability of the structure, but when the doping concentration was increased, the bond breaks simultaneously which led to having four and five free atoms for 8.33%, and 12.5% of F doped MoO2 respectively. This makes 4.17% of F doped MoO2 with 17.09Ry more stable. Similarly, the bond length of undoped MoO2 was 2.2505pm, but when doped with ...