Electronic structure of sodium tungsten bronzesNaxWO3by high-resolution angle-resolved photoemission spectroscopy

Abstract

The electronic structure of sodium tungsten bronzes, Na x WO 3 , for full range of x is investigated by highresolution angle-resolved photoemission spectroscopy ͑HR-ARPES͒. The experimentally determined valenceband structure has been compared with the results of ab initio band-structure calculation. The HR-ARPES spectra taken in both the insulating and metallic phase of Na x WO 3 reveal the origin of metal-insulator transition ͑MIT͒ in the sodium tungsten bronze system. In the insulating Na x WO 3 , the near-E F states are localized due to the strong disorder caused by the random distribution of Na + ions in WO 3 lattice. While the presence of an impurity band ͑level͒ induced by Na doping is often invoked to explain the insulating state found at low concentrations, there is no signature of impurity band ͑level͒ found from our results. Due to disorder and Anderson localization effect, there is a long-range Coulomb interaction of conduction electrons; as a result, the system is insulating. In the metallic regime, the states near E F are populated and the Fermi level shifts upward rigidly with increasing electron doping ͑x͒. The volume of electronlike Fermi surface ͑FS͒ at the ⌫͑X͒ point gradually increases with increasing Na concentration due to W 5dt 2g band filling. A rigid shift of E F is found to give a qualitatively good description of the FS evolution.

Near Infrared Shielding Properties of Quaternary Tungsten Bronze Nanoparticle Na0.11Cs0.22WO3

“…15 In our result, the cubic phase was formed at the sodium fraction of 0.11 possibly due to our high temperature solid state reaction condition for a quaternary compound. The portion of the cubic phase can be up to 33% as the addition ratio of sodium and cesium is 1:2 in the quaternary compound.…”

“…5 These features indicate that the band structures of Cs 0.33 WO 3 , formed by electron contribution from metal ions to the tungsten conduction band, are delocalized possibly due to the incorporation of large cesium element, resulting in more distorted crystal structures. 15 CsHTBs can thus show good performance for NIR shielding in a wider range of NIR wavelength. When sodium is added to the Cs-HTBs at a 0.11 mole fraction while maintaining the overall metal fraction at 0.33, the resulting Na 0.11 Cs 0.22 WO 3 nanoparticles present a broad absorption similar to CsHTBs.…”

METAL-INSULATOR TRANSITION OF NaxWO3 STUDIED BY ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY

“…Höchst et al 15 have performed angle-resolved photoemission spectroscopy (ARPES) on metallic Na 0.85 WO 3 single crystal with relatively low energy and momentum resolutions, and very recently we have carried out systematic high-resolution ARPES experiments on Na x WO 3 for the full range of x. [20][21][22][23] Moreover, due to the previous low energy and angular resolution of the experimental data, it was difficult to compare the experimental results with available band calculations. [24][25][26] The evolution of electronic structure with x in the metallic regime was also not clear from the previous studies.…”

Ab initio probing of the electronic band structure and Fermi surface of fluorine-doped WO3 as a novel low-T C superconductor

“…Note that a similar trend was found for the related system: sodium tungsten bronze Na x WO 3 , where Na ions intercalated into WO 3 lattice behave as electron dopants. Here, by means of the high-resolution angle-resolved photoemission spectroscopy (HR-ARPES), the Fermi surface was found [18,19] to increase with Na concentration (i.e. with an increase in the electron doping level).…”

“…So, the increase in the lattice constant of tungsten oxyfluoride with a growth of F content (in spite of the fact that R(F with a larger radius during fluorination. We carried out a Bader [19] analysis, and the calculated effective atomic charges Q for ideal WO 3 the effective atomic charges decrease, but in general the inter-atomic charge transfer is much smaller than it is predicted in the aforementioned idealized ionic model. This can be explained by the peculiarities of inter-atomic bonding in WO 3 [13][14][15][16][17] and WO 2.5 F 0.5 , which is of a mixed ionic-covalent type, when, besides ionic bonding, moderate covalent W-O (W-F) interactions arise owing to hybridization of W 5d -O 2p (W 5d -F 2p) states, see Fig.…”