A combined computational and experimental investigation of Mg doped α-Fe₂O₃

Abstract

In the current work, pristine α-Fe2O3 metal oxide was doped with Mg in an attempt to modulate its electronic properties. To this end, we employed an experimental high throughput strategy, including scanning XRD and optical spectroscopy, which were complimented by atomistic density functional theory (DFT) calculations. The combined study reveals that at Mg/Fe atomic ratios up to ∼1/3, the bandgaps of the hematite-Mg composite materials are similar to that of the pure material. The observed bandgaps are rationalized by electronic band structure and density of states calculations. Additional rationale for the similar bandgaps in pure and doped hematite is provided by topological Bader charge analyses, which indicate that the Mg and Fe ions in the hematite matrix have similar partial atomic charges. Nonetheless, the small charge density difference between the Mg and Fe ions induces a slight spin polarization on both oxygen and Fe ions, resulting in changes in the band edges. Further charge density analyses, using charge density maps and chemical-bonding analyses with the crystal orbital Hamiltonian population scheme, indicate that Mg forms ionic bonds with the neighboring oxygen atoms. This change from iron-oxygen covalent bonds to a more ionic nature for magnesium-oxygen bonds is probably responsible for the reduction observed in the computed bulk modulus of α-Mg(0.17)Fe(1.83)O3 (193 GPa) compared to α-Fe2O3 (202 GPa).

Tuning the Hematite (110) Surface Properties To Enhance Its Efficiency in Photoelectrochemistry

“…This is in contrast to previous findings on narrowing the energy gap in the studies The Journal of Physical Chemistry C Article using bulk geometry. [21][22][23]73 This discrepancy can be explained by the different content of the heteroatoms in those works compared to our model. In the cited papers, in bulk geometry, the content of subatoms ranged from a few to about 10%, while in our calculations, we use one heteroatom atom per 95 Fe atoms.…”

“…Kosa et al reported a combined theoretical and experimental study on Mg doping. 22 They show that Mg doping of different concentrations has no significant effect on the band gap, and despite the difference in the oxidation state, the system shows no introduction of holes. They ascribe it to similar effective partial charge on Mg and Fe atoms.…”

Iron cation vacancies in Pt(iv)-doped hematite

“…Mg 2+ -Doped hematite is known to alter its mechanical properties and make it softer. 53 Like Al, Mg contents in our hematite are constant at 0.25 AE 0.01 apfu. Ti 4+ -Doping is likewise occasionally employed to improve water oxidation efficiency.…”

The “Rust” Challenge: On the Correlations between Electronic Structure, Excited State Dynamics, and Photoelectrochemical Performance of Hematite Photoanodes for Solar Water Splitting

“…[29][30][31][32] The resulting Fe-O bond is partially ionic and covalent in nature, as calculated by Bader charge analysis to have an effective charge of +1.8 on iron and -1.2 on oxygen using the conventional Density Functional Theory (DFT)+U method. [18,31,33] The "+U" factor has been introduced more than a few decades ago [34,35] to address the strong correlation of open shell transition metal d orbitals, positioning hematite as a benchmark for correlated electronic structure calculations. The energy band structure of hematite has been partially resolved using state-ofthe-art electronic structure theories, such as wave-function based methods, hybrid functionals, and manybody Green's function method with screened Coulomb potential W, known as the GW approximation (GWA).…”