Nuclear magnetic resonance of 19F in rare earth trifluorides

Saraswati, V.; Vijayaraghavan, R.

doi:10.1016/0022-3697(67)90233-8

Cited by 24 publications

(7 citation statements)

References 16 publications

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“…Early 19 F wide-line NMR spectra of polycrystalline rare-earth fluorides REF 3 (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb) − were reported, with two distinct resolved lines, corresponding to the two inequivalent fluorine sites of orthorhombic HoF 3 , ErF 3 , and YbF 3 . 19 F NMR spectra of REF 3 single crystals (RE = Ce, Tb and Ho, Nd and Pr, Er) with distinct resolved lines, corresponding to the inequivalent fluorine sites, were also reported.…”

Section: Resultsmentioning

confidence: 99%

Exploring the Sm_1–xCa_xF_3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F^– Ionic Conductivity

et al. 2015

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Pure tysonite Sm1–x Ca x F3–x solid solutions for 0.05 ≤ x ≤ 0.17 have been prepared by the solid-state route. For the first time, the partial Sm1–x Ca x F3–x solid solution is investigated on the basis of structural features and ionic conductivity measurements. Powder X-ray diffraction Rietveld refinements show an unexpected decrease of the hexagonal unit cell volume related to the creation of fluorine vacancies. The local environment of F1, which is mainly responsible for the ionic conductivity, changes with the Ca content: the distortion of the F1(Sm,Ca)4 tetrahedral site decreases with the Ca content. Fluoride ion exchanges have been qualitatively probed on two Sm1–x Ca x F3–x (x = 0.05 and x = 0.15) samples thanks to 19F magic angle spinning NMR experiments at various spinning frequencies and temperatures. At room temperature, the ionic conductivity decreases exponentially with the Ca content and the activation energy increases monotonously with the Ca content. The highest conductivity is found for the lowest Ca content or the smallest fluorine vacancy content stabilized in the Sm1–x Ca x F3–x tysonite network corresponding to Sm0.95Ca0.05F2.95 (10–4 S·cm–1, E a = 0.36 eV at room temperature). For this composition, the largest dispersions of F2–(Sm,Ca) and F3–(Sm,Ca) distances as well as (Sm,Ca)–F1–(Sm,Ca) angles are observed. The buckling of F2/F3 sheets around the z = 1/4 coordinate for low Ca content affects the large F1 tetrahedral site with the strongest distortion. The higher the buckling effect into the F2/F3 sheets, the higher the F1 local site distortion and the higher the ionic mobility and conductivity.

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Section: Resultsmentioning

confidence: 99%

Exploring the Sm_1–xCa_xF_3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F^– Ionic Conductivity

et al. 2015

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“…Bulk Crystalline Lanthanum Trifluoride, 1. LaF 3 has been well characterized by a number of techniques, including single-crystal X-ray − and neutron diffraction, solid-state 19 F NMR − and 139 La NMR, , as well as variable-temperature 139 La nuclear quadrupole resonance (NQR) experiments. , Numerous structures of LaF 3 have been reported involving different space groups, cell dimensions, and atomic positions (see above references). The currently accepted structure is found in a combined X-ray and neutron-diffraction study on a single-crystal of LaF 3 by Maximov et al They reported a single lanthanum site and three distinct fluorine sites (denoted as F1, F2, and F3); however, the fluoride ions are known to undergo dynamic exchange, which may be largely responsible for the ionic conduction in LaF 3 . − , The local structure centered at the La site is depicted in Chart A.…”

Section: Resultsmentioning

confidence: 99%

“…The S / N of the F1 resonance is considerably reduced, and the center of gravity shifts to −34 ppm (compared to −23.1 ppm in the spectrum of 2 ). The increased broadening of the powder patterns with higher sample doping arises predominantly from paramagnetic relaxation induced by unpaired electrons and possibly anisotropic broadening resulting from dipolar coupling with the unpaired spin density on the Yb atom. , The extreme broadening makes it impossible to accurately measure the isotropic chemical shift; however, the apparent negative shift may result from a pseudo-contact interaction with the unpaired electron . The most important feature of the 19 F NMR spectra of 3 and 4 is the absence of intense, unshifted, and unbroadened resonances, indicating that the Yb 3+ dopants are homogeneously distributed throughout the LaF 3 NP cores.…”

Section: Resultsmentioning

confidence: 99%

Multinuclear Solid-State NMR Spectroscopy of Doped Lanthanum Fluoride Nanoparticles

Sudarsan

Sivakumar

et al. 2007

J. Am. Chem. Soc.

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Multinuclear solid-state NMR spectroscopy and powder X-ray diffraction (XRD) experiments are applied to comprehensively characterize a series of pure and lanthanide-doped LaF3 nanoparticles (NPs) that are capped with di-n-octadectyldithiophosphate ligands (Ln3+ = diamagnetic Y3+ and Sc3+ and paramagnetic Yb3+ ions), as well as correlated bulk microcrystalline materials (LaF3, YF3, and ScF3). Solid-state 139La and 19F NMR spectroscopy of bulk LaF3 and the LaF3 NPs reveal that the inorganic core of the NP retains the LaF3 structure at the molecular level; however, inhomogeneous broadening of the NMR powder patterns arises from distributions of 139La and 19F NMR interactions, confirming a gradual change in the La and F site environments from the NP core to the surface. 139La and 19F NMR experiments also indicate that low levels (5 and 10 mol %) of Ln3+ doping do not significantly change the LaF3 structure in the NP core. Similar doping levels of paramagnetic Yb3+ ions severely broaden 19F resonances, but only marginally effect 139La powder patterns, suggesting that the dopant ions are uniformly distributed throughout the NP core and occupy vacant La sites. Measurements of 139La T1 and T2 relaxation constants are seen to vary between the bulk material and NPs and between samples with diamagnetic and paramagnetic dopants. 45Sc NMR experiments confirm that the dopants are integrated into the La sites of the LaF3 core. Solid-state 1H and 31P magic-angle spinning (MAS) NMR spectra aid in probing the nature of the capping ligands and their interactions at the NP surface. 31P cross-polarization (CP)/MAS NMR experiments identify not only the dithiophosphate head groups but also thiophosphate and phosphate species which may form during NP synthesis. Finally, 19F-31P CP/MAS and 1H MAS experiments confirm that ligands are coordinated to the NP surface.

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“…The available data [42][43][44][45][46] are confined to O 17 and F 19 isotropic hyperfine coupling constants for hydrated ions or fluoride salts, and we have converted them to hyperfine fields by dividing by the appropriate nuclear gyromagnetic ratio 7. To compare them fairly with compounds having the NaCl structure it is necessary to increase them by the ratio of ligands to metal atoms, and we list these results in Table VI.…”

Section: K=kotl+j Sf (Gj-l)x/2ngj^mentioning

confidence: 99%

Knight Shifts ofC13in the Carbides of Uranium and Thorium

et al. 1968

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The C 13 nuclear magnetic resonance has been observed in the unenriched carbides of thorium and uranium ThC, TI1C2, UC, U2C3, and UC2. In contrast to nearly all nonmagnetic metals and semimetallic compounds, the Knight shift in the semimetallic thorium carbides is negative. On the other hand, the Knight shifts in all of the uranium carbides are positive, which is consistent with the P 31 shift in UP and PrP. The C 13 Knight shift in all of the carbides except U2C3 was temperature-independent. On the basis of magnetic susceptibility evidence, it is found that the uranium carbides are similar to other semimetallic uranium compounds in that their magnetic properties are best explained at higher temperatures with a localized /-electron model with large crystal-field splitting. The C 13 Knight shift in the uranium carbides is interpreted in terms of an effective hyperfme field resulting from the presence of two 5/ electrons in UC and UC2 and three in U 2 C 3 . Only the lowest crystal-field level of the 3 # 4 configuration (the nonmagnetic level Ti in the case of UC) is appreciably populated in UC and UC2. A comparison of hyperfme fields in a variety of lanthanide and actinide compounds suggests that the fields in semimetallic compounds and insulators have similar origins and that the differences are associated largely with structure, covalency, and overlap, and not with the presence or absence of conduction electrons.

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Nuclear magnetic resonance of 19F in rare earth trifluorides

Cited by 24 publications

References 16 publications

Exploring the Sm_1–xCa_xF_3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F^– Ionic Conductivity

Exploring the Sm_1–xCa_xF_3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F^– Ionic Conductivity

Multinuclear Solid-State NMR Spectroscopy of Doped Lanthanum Fluoride Nanoparticles

Knight Shifts ofC13in the Carbides of Uranium and Thorium

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Nuclear magnetic resonance of 19F in rare earth trifluorides

Cited by 24 publications

References 16 publications

Exploring the Sm1–xCaxF3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F– Ionic Conductivity

Exploring the Sm1–xCaxF3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F– Ionic Conductivity

Multinuclear Solid-State NMR Spectroscopy of Doped Lanthanum Fluoride Nanoparticles

Knight Shifts ofC13in the Carbides of Uranium and Thorium

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Exploring the Sm_1–xCa_xF_3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F^– Ionic Conductivity

Exploring the Sm_1–xCa_xF_3–x Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F^– Ionic Conductivity