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Modelling the chemistry of Mn-doped MgO for bulk and (100) surfaces

Logsdail, AJ; Downing, CA; Keal, TW; Sherwood, P; Sokol, AA; Catlow, CRA; (2016) Modelling the chemistry of Mn-doped MgO for bulk and (100) surfaces. Physical Chemistry Chemical Physics , 18 (41) pp. 28648-28660. 10.1039/c6cp04622c. Green open access

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Abstract

We have investigated the energetic properties of Mn-doped MgO bulk and (100) surfaces using a QM/MM embedding computational method, calculating the formation energy for doped systems, as well as for surface defects, and the subsequent effect on chemical reactivity. Low-concentration Mn doping is endothermic for isovalent species in the bulk but exothermic for higher oxidation states under p-type conditions, and compensated by electrons going to the Fermi level rather than cation vacancies. The highest occupied dopant Mn 3d states are positioned in the MgO band gap, about 4.2 eV below the vacuum level. Surface Mn-doping is more favourable than subsurface doping, and marginally exothermic on a (100) surface at high O2 pressures. For both types of isovalent Mn-doped (100) surfaces, the formation energy for catalytically important oxygen defects is less than for pristine MgO, with F0 and F2+-centres favoured in n- and p-type conditions, respectively. In addition, F+-centres are stabilised by favourable exchange coupling between the Mn 3d states and the vacancy-localised electrons, as verified through calculation of the vertical ionisation potential. The adsorption of CO2 on to the pristine and defective (100) surface is used as a probe of chemical reactivity, with isovalent subsurface Mn dopants mildly affecting reactivity, whereas isovalent surface-positioned Mn strongly alters the chemical interactions between the substrate and adsorbate. The differing chemical reactivity, when compared to pristine MgO, justifies further detailed investigations for more varied oxidation states and dopant species.

Type: Article
Title: Modelling the chemistry of Mn-doped MgO for bulk and (100) surfaces
Open access status: An open access version is available from UCL Discovery
DOI: 10.1039/c6cp04622c
Publisher version: http://dx.doi.org/10.1039/c6cp04622c
Language: English
Additional information: This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (http://creativecommons.org/licenses/by/3.0/).
Keywords: science & technology, physical sciences, chemistry, physical, physics, atomic, molecular & chemical, chemistry, physics, ab-initio calculations, oxide surfaces, oxygen vacancy, electronic-structure, MGO(100) surface, solid-solutions, density, QM/MM, CO2, transition
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/1531020
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