Vacancy-induced in-gap states in sodium tungsten bronzes: Density functional investigations

Abstract

We have performed extensive ab-initio self-consistent electronic-structure calculations on WO3 and NaWO3 with single-and double-oxygen-vacancy defects within the framework of density functional theory. Our calculated density of states reveals that the in-gap states in WO3 and NaWO3 are the consequence of oxygen vacancies in the system. The evolution of the induced states occurs from the unpaired electrons donated by the oxygen vacancy. We found that the energy positions of the in-gap states are sensitive to the oxygen vacancy concentrations. The in-gap states in NaWO3 are formed close to the valence band, which are pushed towards the conduction band with the increase in oxygen vacancies, whereas the states are formed mostly in the mid-gap region in the WO3 system. Our finding can now well explain the discrepancy in experimental band dispersion measurements from ARPES with that of WO3 and NaWO3 band calculations.

The sodium tungsten bronzes as plasmonic materials: fabrication, calculation and characterization

“…The structure of the DOS presented here for x = 0.000 and x = 1.000 closely matches that reported in earlier density functional investigations [63,64]. DOS for the other compositions has not previously been reported in the literature.…”

Tungsten-titanium mixed oxide bronzes: Synthesis, characterization and catalytic behavior in methanol transformation

“…This behavior could tentatively be explained if we take into consideration the specific properties of the tungsten bronze-type materials under oxidative or reducing conditions, especially their non-stoichiometric nature [5]. The generation of oxygen vacancies, and their effect on functional properties of this type of materials is widely reported in literature [46][47][48][49][50]. Specifically, reduction or vacuum treatments at high temperatures favor the creation of anionic vacant sites [51,52].…”