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A van der Waals Density Functional Study of MoO3 and Its Oxygen Vacancies
journal contribution
posted on 2016-04-08, 00:00 authored by Katherine Inzani, Tor Grande, Fride Vullum-Bruer, Sverre M. SelbachThe
electronic structure of layered molybdenum trioxide MoO3 is highly sensitive to changes in oxygen stoichiometry as
Mo6+ has an empty 4d shell. Applications of MoO3 are responsive to small changes in vacancy concentration, with some
functions relying on a narrow window of oxygen nonstoichiometry. Difficulties
in analyzing the energetics of oxygen vacancies by computational methods
stem from the inability to accurately model the layered structure
of MoO3. One unit cell parameter is governed by long-range
forces across the structural gaps, and these dispersed interactions
are not well described by conventional density functional theory (DFT)
methods. With the exchange functional vdW-DF2, we accurately model
the structure, in good agreement with experimental data. This basis
allows exploration of the effect of oxygen nonstoichiometry on the
electronic structure and properties of the oxygen-deficient material.
The layered structure efficiently screens the structural perturbations
caused by oxygen vacancies. The enthalpies of formation are calculated
for oxygen vacancies at the three symmetry inequivalent oxygen sites.
The oxygen deficiency in MoO3 gives rise to Mo 4d gap states
with energy levels dependent on the type of oxygen vacancy.