60 research outputs found
First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6
First principles calculations based on the density functional theory within
the local spin density approximation plus U(LSDA+U)scheme, show rhombohedral
BiFeTiO is a potential multiferroic in which the magnetism and
ferroelectricity coexist . A ferromagnetic configuration with magnetic moment
of 4 per formula unit have been reported with respect to the minimum
total energy. Spontaneous polarization of 27.3 C/cm, caused mainly by
the ferroelectric distortions of Ti, was evaluated using the berry phase
approach in the modern theory of polarization. The Bi-6s stereochemical
activity of long-pair and the `d-ness' criterion in off-centring of Ti were
coexisting in the predicted new system. In view of the oxidation state of
Bi,Fe,Ti, and O from the orbital-resolved density
of states of the Bi-6p, Fe-3d,Ti-3d, and O-2p states,the valence state of
BiFeTiO in the rhombohedral phase was found to be
BiFeTiO.Comment: 22 pages, 9 figures. submitted to Physics Letters
Hazardous Doping for Photo-Electrochemical Conversion: The Case of Nb-Doped Fe2O3 from First Principles
The challenge of improving the efficiency of photo-electrochemical devices is often addressed through doping. However, this strategy could harm performance. Specifically, as demonstrated in a recent experiment, doping one of the most widely used materials for water splitting, iron (III) oxide (Fe2O3), with niobium (Nb) can still result in limited efficiency. In order to better understand the hazardous effect of doping, we use Density Functional Theory (DFT)+U for the case of Nb-doped Fe2O3. We find a direct correlation between the charge of the dopant, the charge on surface of the Fe2O3 material, and the overpotential required for water oxidation reaction. We believe that this work contributes to advancing our understanding of how to select effective dopants for materials
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