The Science & Technology
Cambridge - Monday 4th to
Wednesday 6th September 2017
article posted 19 June 2017
Thibault Charpentier has been working in CEA Saclay since 1998 when he received his Ph.D. (NMR of quadrupolar nuclei in solids). His research interest is both theoretical with methodological
developments in solid state NMR and experimental with application of NMR to glass science. He is working in the field of NMR Theory and computational modelling of NMR in glasses involving DFT–GIPAW
calculations combined with molecular dynamics simulations. He developed dedicated methodologies to elucidate the structure of glasses and more specifically nuclear waste glasses.
Combined Solid-State NMR and Molecular Dynamics Study of the Structure of Strontium-Aluminosilicate glasses
Thibault Charpentier*1, Kirill Okhotnikov1, Pierre Florian2, Frank Fayon2, Alexey Novikov2,3, Louis Hennet2, Daniel R. Neuville3
Aluminosilicate based glasses are widely used in glass industry and their atomic-scale structural and dynamical properties have been thoroughly investigated using various spectroscopic
methods. Among them, solid state NMR has firmly established itself as a method of choice for providing key information for the elucidation of their atomic-scale structure. Recently, a
methodology based on the combination of DFT-NMR calculations with molecular dynamics simulations has emerged as a significant step towards the improvement of the detailed interpretation
of experimental NMR spectra.
Using this approach, we have investigated the structure of aluminosilicate SiO2
-SrO based glass compositions which are largely unexplored systems. Glasses on the compensation line
3 = SrO, were studied with 17
Si and 27
Al solid state NMR at high (11.7 T) and very-high (20.0 T) magnetic fields, together with neutron diffraction spectroscopy. Classical and
ab-initio molecular dynamics (MD) simulations were performed and combined with calculations of NMR parameters with the DFT-GIPAW method. Concerning MD, two analytical forms of the
force-fields potentials (Morse and Buckingham) were compared for the description of the short-range interatomic interactions. Computed NMR parameters were linked to local structural
features to establish relationships between experimental NMR spectra and the underlying topological disorder (in terms of chemical and geometrical disorder). NMR fingerprints of
debated units such as tricoordinated oxygen atoms could be predicted with the aim to assess their existence from experimental data.
In agreement with experimental NMR data, MD simulations predict that aluminium is predominantly tetrahedrally coordinated for all the studied compositions with a small fraction of
AlO5 units ranging from 2-5%mol. Variations of the 29
Si NMR spectra, and to a less extent of 27
Al spectra, could be quantitatively correlated to the Al/Si mixing. In parallel, the
Al/Si connectivities were investigated using advanced NMR techniques enabling the resolution of the 29
Si NMR spectrum in terms of Qn
(mAl) units (i.e., Qn
connected to m Al units).
Simulations of 17
O NMR experiments from our first-principles methodology combined to 17
Al correlation experiments allowed the extraction of Al-O-Si, Al-O-Al and Si-O-Si peaks
which were found to be strongly overlapping in experimental 1D and 2D 17
O MAS NMR spectra.
This study illustrates well this novel methodology which allows quantifying the medium-range order of amorphous materials by comparison of NMR results with first-principle NMR parameters
calculations performed on Molecular Dynamic derived structures.
NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, France.
CNRS, CEMHTI UPR3079, Univ. Orléans, France.
CNRS-IPGP, Paris Sorbonne Cité, France.