Center for Molecular Modeling - I. Van Driessche

Aliovalent doping of CeO2: DFT study of oxidation state and vacancy effects

danny — Thu, 03 Jul 2014 14:02:03 +0000

D.E.P. Vanpoucke, P. Bultinck, S. Cottenier, V. Van Speybroeck, I. Van Driessche

Journal of Materials Chemistry A

2 (3), 13723-13737

2014

Abstract

The modification of CeO₂ properties by means of aliovalent doping is investigated within the ab initio density functional theory framework. Lattice parameters, dopant atomic radii, bulk moduli and thermal expansion coefficients of fluorite type Ce_1-xM_xO_2-y (with M = Mg, V, Co, Cu, Zn, Nb, Ba, La, Sm, Gd, Yb, and Bi) are presented for 0.00 < x < 0.25. The relative stability of the doped systems is discussed, and the influence of oxygen vacancies is investigated. It is shown that oxygen vacancies tend to increase the lattice parameter, and strongly decrease the bulk modulus. Defect formation energies are correlated with calculated crystal radii and covalent radii of the dopants, and are shown to present no simple trend. The previously observed inverse relationship between the thermal expansion coefficient and the bulk modulus in group IV doped CeO2 [J. Am. Ceram. Soc., 2014, 97(1), 258] is shown to persist independent of the inclusion of charge compensating vacancies.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/c4ta02449d

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14_JMatChem_2,13723_Vanpoucke.pdf

Tetravalent doping of CeO2: The impact of valence electron character on group IV dopant influence

wim — Fri, 22 Nov 2013 07:34:14 +0000

D.E.P. Vanpoucke, S. Cottenier, V. Van Speybroeck, I. Van Driessche, P. Bultinck

Journal of the American Ceramic Society

97 (1), 258-266

2014

Abstract

Fluorite CeO2 doped with group IV elements is studied within the DFT and DFT+U framework. Concentration dependent formation energies are calculated for Ce1−xZxO2 (Z= C, Si, Ge, Sn, Pb, Ti, Zr, Hf) with 0≤x≤0.25 and a roughly decreasing trend with ionic radius is observed. The influence of the valence and near valence electronic configuration is discussed, indicating the importance of filled d and f shells near the Fermi level for all properties investigated. A clearly different behavior of group IVa and IVb dopants is observed: the former are more suitable for surface modifications, the latter are more suitable for bulk modifications.\\ \indent For the entire set of group IV dopants, there exists an inverse relation between the change, due to doping, of the bulk modulus and the thermal expansion coefficients. Hirshfeld-I atomic charges show that charge transfer effects due to doping are limited to the nearest neighbor oxygen atoms.

DOI

http://dx.doi.org/10.1111/jace.12650

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13_AmerCerSoc_97(1)258_VanPoucke.pdf

Reply to ‘comment on “extending hirshfeld-I to bulk and periodic materials”’

danny — Tue, 12 Feb 2013 09:13:04 +0000

D.E.P. Vanpoucke, I. Van Driessche, P. Bultinck

Journal of Computational Chemistry

Volume 34, Issue 5, pages 422-427

2013

Published while none of the authors were employed at the CMM

Abstract

The issues raised in the comment by Manz are addressed through the presentation of calculated atomic charges for NaF, NaCl, MgO, SrTiO₃ , and La₂Ce₂O₇ , using our previously presented method for calculating Hirshfeld-I charges in solids (Vanpoucke et al., J. Comput. Chem. doi: 10.1002/jcc.23088). It is shown that the use of pseudovalence charges is sufficient to retrieve the full all-electron Hirshfeld-I charges to good accuracy. Furthermore, we present timing results of different systems, containing up to over 200 atoms, underlining the relatively low cost for large systems. A number of theoretical issues are formulated, pointing out mainly that care must be taken when deriving new atoms in molecules methods based on “expectations” for atomic charges.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1002/jcc.23193

Extending Hirshfeld-I to bulk and periodic materials

danny — Tue, 12 Feb 2013 09:07:46 +0000

D.E.P. Vanpoucke, P. Bultinck, I. Van Driessche

Journal of Computational Chemistry

Volume 34, Issue 5, pages 405-417

2013

Published while none of the authors were employed at the CMM

Abstract

In this work, a method is described to extend the iterative Hirshfeld-I method, generally used for molecules, to periodic systems. The implementation makes use of precalculated pseudopotential-based electron density distributions, and it is shown that high-quality results are obtained for both molecules and solids, such as ceria, diamond, and graphite. The use of grids containing (precalculated) electron densities makes the implementation independent of the solid state or quantum chemical code used for studying the system. The extension described here allows for easy calculation of atomic charges and charge transfer in periodic and bulk systems. The conceptual issue of obtaining reference densities for anions is discussed, and the delocalization problem for anionic reference densities originating from the use of a plane wave basis set is identified and handled.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1002/jcc.23088

Aqueous CSD approach for the growth of novel, lattice-tuned LaxCe1-xOδ epitaxial layers

wim — Tue, 18 Dec 2012 12:18:54 +0000

V. Narayanan, P. Lommens, K. De Buysser, D.E.P. Vanpoucke, R. Hühne, L. Molina, G. Van Tendeloo, P. Van der Voort, I. Van Driessche

Journal of Materials Chemistry

22 (17), 8476-8483

2012

Published while none of the authors were employed at the CMM

DOI

http://dx.doi.org/10.1039/c2jm15752g

Quantification of silanol sites for the most common mesoporous ordered silicas and organosilicas: total versus accessible silanols

wim — Wed, 07 Nov 2012 13:38:27 +0000

M. Ide, M. El-Roz, E. De Canck, A. Vicente, T. Planckaert, T. Bogaerts, I. Van Driessche, F. Lynen, V. Van Speybroeck, F. Thibault-Starzyk, P. Van der Voort

Physical Chemistry Chemical Physics (PCCP)

15, 642-650

2013

Abstract

IR and NMR spectroscopy were used to determine the silanol content in the most common mesoporous ordered silicas: MCM-41, MCM-48, SBA-15 and SBA-16. In addition, a spray dried MCM-41 and an ethene bridged PMO are investigated. The results are compared with a commercial chromatographic silica (Nucleosil). The complete distribution of surface and bulk silanols, and of isolated, geminal and vicinal silanols for all these materials is presented. A distinction is made between the total silanol number and the reachable or surface silanol content. The latter is determined by controlled reactions with simple silanes. All mesoporous ordered silicas, and especially the thick walled SBA-type materials and the PMO contain a surprisingly high amount of total silanol sites, albeit that up to 90% if these silanols are buried inside the walls and are not reachable for small silanes.

DOI

http://dx.doi.org/10.1039/C2CP42811C

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13_PCCP_15_642_ide.pdf

Tuning of CeO2 buffer layers for coated superconductors through doping

wim — Thu, 18 Oct 2012 07:05:20 +0000

D.E.P. Vanpoucke, S. Cottenier, V. Van Speybroeck, P. Bultinck, I. Van Driessche

Applied Surface Science

260, 32-35

2012

Abstract

The appearance of microcracks in cerium oxide (CeO 2) buffer layers, as used in buffer layer architectures for coated superconductors, indicates the presence of stress between this buffer layer and the substrate. This stress can originate from the differences in thermal expansion or differences in lattice parameters between the CeO 2 buffer layer and the substrate. In this article, we study, by means of ab initio density functional theory calculations, the influence of group IV doping elements on the lattice parameter and bulk modulus of CeO 2. Vegard's law behavior is found for the lattice parameter in systems without oxygen vacancies, and the Shannon crystal radii for the doping elements are retrieved from the lattice expansions. We show that the lattice parameter of the doped CeO 2 can be matched to that of the La 2Zr 2O 7 coated NiW substrate substrate for dopant concentrations of about 5%, and that bulk modulus matching is either not possible or would require extreme doping concentrations. [All rights reserved Elsevier].

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1016/j.apsusc.2012.01.032

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12_app. surface sc_260_32_Vanpoucke.pdf

Synthesis, characterization and sorption properties of NH2-MIL-47

mat — Thu, 22 Mar 2012 08:36:33 +0000

K. Leus, S. Couck, M. Vandichel, G. Vanhaelewyn, Y-Y Liu, G.B. Marin, I. Van Driessche, D. Depla, M. Waroquier, V. Van Speybroeck, J.F.M. Denayer, P. Van der Voort

Physical Chemistry Chemical Physics (PCCP)

14, 15562–15570

2012

Abstract

An amino functionalized vanadium-containing Metal Organic Framework, NH₂-MIL-47 has been synthesized by a hydrothermal reaction in an autoclave. Alternatively, a synthesis route via microwave enhanced irradiation has been optimized to accelerate the synthesis. The NH₂-MIL-47 exhibits the same topology as MIL-47, in which the V center is octahedrally coordinated. After an exchange procedure in DMF the V+III center is oxidized to V+IV, which is confirmed by EPR and XPS measurements. The CO² and CH₄ adsorption properties have been evaluated and compared to MIL-47, showing that both MOFs have an almost similar adsorption capacity and affinity for CO². DFT- based molecular modeling calculations were performed to obtain more insight into the adsorption positions for CO² in NH₂-MIL-47. Furthermore our calculated adsorption enthalpies agree well with the experimental values.

DOI

http://dx.doi.org/10.1039/C2CP42137B

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12 pccp 14,15562 Leus.pdf

Density functional theory study of La2Ce2O7: Disordered fluorite versus pyrochlore structure

wim — Mon, 22 Aug 2011 09:57:01 +0000

D.E.P. Vanpoucke, P. Bultinck, S. Cottenier, V. Van Speybroeck, I. Van Driessche

Physical Review B

84, 054110

2011

Abstract

The crystal structure of lanthanum cerium oxide (La2Ce2O7) is investigated using ab initio density functional theory calculations. The relative stability of fluorite- and pyrochlorelike structures is studied through comparison of their formation energies. These formation energies show the pyrochlore structure to be favored over the fluorite structure, apparently contradicting the conclusions based on experimental neutron and x-ray diffraction (XRD). By calculating and comparing XRD spectra for a set of differently ordered and random structures, we show that the pyrochlore structure is consistent with diffraction experiments. For these reasons, we suggest the pyrochlore structure as the ground-state crystal structure for La2Ce2O7. © 2011 American Physical Society

DOI

http://dx.doi.org/10.1103/PhysRevB.84.054110

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11 Phys Rev B 84 054110 vanpoucke.pdf

Tuning of CeO2 buffer layers for coated superconductors through metal doping

samuel — Thu, 06 Feb 2020 13:44:12 +0000

D.E.P. Vanpoucke, S. Cottenier, V. Van Speybroeck, P. Bultinck, I. Van Driessche

ISBN/ISSN:

Talk

Conference / event / venue

E-MRS 2011 Fall Meeting

Warsaw, Poland

Monday, 19 September, 2011 to Friday, 23 September, 2011