NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations

Sadoc, Aymeric; Body, Monique; Legein, Christophe; Biswal, Mamata; Fayon, Franck; Rocquefelte, Xavier; Boucher, Florent

doi:10.1039/c1cp21253b

Cited by 123 publications

(186 citation statements)

References 123 publications

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“…As expected, coarse grained SrF 2 only shows a single resonance at −84.8 ppm and the spectrum of YF 3 reveals the two crystallographically inequivalent F positions F(1) and F(2). The samples with µm-sized crystallites are composed of sharp lines that perfectly agree with those presented and analyzed in literature [30,31]. Broadening, but no change in isotropic chemical shift, is observed for the samples treated mechanically.…”

Section: Structure: X-ray Diffraction and 19 F High-resolution Mas Nmsupporting

confidence: 71%

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

Breuer¹,

Stanje²,

Pregartner³

et al. 2018

Preprint

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Nanostructured materials have already become an integral part of our daily life. In many applications ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and disordered interfacial regions. In particular, anion conductivity in nonstructural binary fluorides easily exceeds that of their coarse-grained counterparts. To further increase ion dynamics aliovalent substitution is a practical method to influence the number of (i) defect sites and (ii) the charge carrier density. Here, we used high energy-ball milling to incorporate Y 3+ ions into the cubic structure of SrF 2 . As compared to pure nanocrystalline SrF 2 the ionic conductivity of Sr 1−x Y x F 2+x with x = 0.3 increased by 4 orders of magnitude reaching 0.8 × 10 −5 S cm −1 at 450 K. We discuss the effect of YF 3 incorporation on conductivities isotherms determined by both activation energies and Arrhenius pre-factors. The enhancement seen is explained by size mismatch of the cations involved, which are forced to form a cubic crystal structure with extra F anions if x is kept smaller than 0.5.

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Section: Structure: X-ray Diffraction and 19 F High-resolution Mas Nmsupporting

confidence: 71%

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

Breuer¹,

Stanje²,

Pregartner³

et al. 2018

Preprint

View full text Add to dashboard Cite

show abstract

“…As expected, coarse grained SrF 2 only shows a single resonance at −84.8 ppm and the spectrum of YF 3 reveals the two crystallographically inequivalent F positions F(1) and F(2). The samples with µm-sized crystallites are composed of sharp lines that perfectly agree with those presented and analyzed in literature [36,40]. Broadening, but no change in isotropic chemical shift, is observed for the samples treated mechanically.…”

Section: Resultssupporting

confidence: 71%

“…The π/2 pulse length was 2.1 µs at 50 W power level; the recycle delay was 20 s and 64 transients were accumulated for each spectrum. We took advantage of LiF powder as a secondary reference (−204.3 ppm) [40] to determine chemical shifts δ iso ; CFCl 3 (0 ppm) served as the primary reference.…”

Section: Methodsmentioning

confidence: 99%

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

et al. 2018

View full text Add to dashboard Cite

Nanostructured materials have already become an integral part of our daily life. In many applications, ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and disordered interfacial regions. In particular, anion conductivity in nonstructural binary fluorides easily exceeds that of their coarse-grained counterparts. To further increase ion dynamics, aliovalent substitution is a practical method to influence the number of (i) defect sites and (ii) the charge carrier density. Here, we used high energy-ball milling to incorporate Y 3+ ions into the cubic structure of SrF 2 . As compared to pure nanocrystalline SrF 2 the ionic conductivity of Sr 1−x Y x F 2+x with x = 0.3 increased by 4 orders of magnitude reaching 0.8 × 10 −5 S cm −1 at 450 K. We discuss the effect of YF 3 incorporation on conductivities isotherms determined by both activation energies and Arrhenius pre-factors. The enhancement seen is explained by size mismatch of the cations involved, which are forced to form a cubic crystal structure with extra F anions if x is kept smaller than 0.5.

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“…The problems manifest mainly in the common observation that within a series of compounds the computed shielding parameters for a particular nucleus show systematic error when compared to the measured values. 13,[15][16][17][18][19][20] For example in the case of fluorides or oxides the shielding parameters computed within DFT using the standard PBE 21 exchange correlation functional are correlate well with the measured values, but the slope of the line representing the relation between the experimental and theoretical data is close to 0.8 instead of 1.0. 15,16 This intriguing and very systematic error has its origin in the deficiencies of the approximate density functional.…”

Section: Introductionmentioning

confidence: 99%

“…13,[15][16][17][18][19][20] For example in the case of fluorides or oxides the shielding parameters computed within DFT using the standard PBE 21 exchange correlation functional are correlate well with the measured values, but the slope of the line representing the relation between the experimental and theoretical data is close to 0.8 instead of 1.0. 15,16 This intriguing and very systematic error has its origin in the deficiencies of the approximate density functional. For instance it has been shown before that for the 17 O chemical shift the error in CaO is significantly larger than for many other oxides and that the problem arises due to Ca 3d orbitals being too close to the valence band maximum, 13 which affects the Ca-3d O-2p hybridization.…”

Section: Introductionmentioning

confidence: 99%

Assessment of DFT functionals with NMR chemical shifts

2013

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Density-functional theory (DFT) calculations of the magnetic shielding for nuclear magnetic resonance (NMR) in solids provide an important contribution for understanding the experimentally observed chemical shifts. It is known that the calculated NMR shielding parameters for a particular nucleus in a series of compounds correlate well with the experimentally measured chemical shifts; however, the slope of a linear fit often differs from the ideal value of 1.0. Focusing on a series of ionic compounds (fluorides, oxides, bromides, and chlorides), we show that the error is caused by the generalized gradient approximation (GGA) to the exchange-correlation functional and it is related to the well-known band-gap problem. In order to devise an ab initio approach that would correctly reproduce the variation of the shifts within a series of compounds, we test various DFT based approaches. A simple GGA + U scheme with the orbital field acting on the cation d states does not work in a general way. Also, the popular hybrid functionals (including the screened versions), which contain some fixed amount of exact exchange, lead to a large overestimation of the necessary slope correction. Surprisingly, the best solution to this problem is offered by a semilocal potential designed by Becke and Johnson to reproduce the optimized exact exchange potential in free atoms. Density functional theory (DFT) calculations of the magnetic shielding for nuclear magnetic resonance (NMR) in solids provide an important contribution for understanding the experimentally observed chemical shifts. It is known that the calculated NMR shielding parameters for a particular nucleus in a series of compounds correlate well with the experimentally measured chemical shifts, however, the slope of a linear fit often differs from the ideal value of 1.0. Focusing on a series of ionic compounds (fluorides, oxides, bromides and chlorides), we show that the error is caused by the generalized gradient approximation (GGA) to the exchange correlation functional and it is related to the well known band-gap problem. In order to devise an ab-initio approach that would correctly reproduce the variation of the shifts within a series of compounds, we test various DFT based approaches. A simple GGA+U scheme with the orbital field acting on the cation d-states does not work in a general way. Also the popular hybrid functionals (like HSE or YS-PBE0), which contain some fixed amount of exact exchange, leads to a large overestimation of the necessary slope correction. Surprisingly, the best solution to this problem is offered by a semi-local potential designed by Becke and Johnson to reproduce the optimized exact exchange potential in free atoms.

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NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations

Cited by 123 publications

References 123 publications

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF2-YF3 Solid Solutions

Assessment of DFT functionals with NMR chemical shifts

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