Solid state NMR characterization of individual compounds and solid solutions formed in Sc₂O₃V₂O₅Nb₂O₅Ta₂O₅ system

Abstract

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).

Structural Studies of Bulk to Nanosize Niobium Oxides with Correlation to Their Acidity

“…However, the large convoluted quadrupolar ( C Q ) and chemical shift anisotropy (CSA) contributions to these line widths often lead to a significant broadening of the central transition resonance, even at very high magnetic field strengths. These complex characteristics describing the 93 Nb static line width often reduce the effectiveness of fast MAS rates when attempting to determine accurate values of the 93 Nb NMR parameters. ,− Octahedrally coordinated NbO 6 environments are normally observed to exhibit δ iso values in the range of ∼−900 to – 1100 ppm, with quadrupole coupling constants ( C Q ) typically ranging from 0 to ∼55 MHz. Four-coordinate NbO 4 and five-coordinate NbO 5 positions generally possess lower point symmetry and are characterized by more downfield δ iso values in the range of ∼−700 to – 850 ppm and very large C Q values of >80 MHz. ,, The tendency for NbO 4 to assume the reduced Nb 4+ oxidation state can result in signals which are influenced significantly by paramagnetic broadening and associated paramagnetic shifts …”

Structural and electrochemical characterization of mesoporous thin films of Nb2xV2−2xO5 upon lithium intercalation

“…2, show two main types of vanadium environments, corresponding to broad lines at 225 ppm and -245 ppm vs. reference. The signal at 225 ppm is attributed to distorted octahedral vanadium (VO 5 +1 ) which is characteristic of the V 2 O 5 layered structure [14]. The feature at -245 ppm corresponds to isolated tetrahedra of VO 4 which are found in the NbVO 5 structure [15].…”

Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in solid-state NMR of spin-7/2 nuclei

“…Recently, a number of solidstate NMR studies has been published involving nuclei with spin I = 7/2, such as 43 Ca [4][5][6], 45 Sc [7][8][9], 49 Ti [10][11][12], 51 V [13][14][15], 139 La [16,17], or a combination of these isotopes [18]. The purpose of such studies is to determine the chemical shift and the quadrupolar interaction parameters, and to correlate them to structure and properties of the compounds under investigation.…”

“…It is demonstrated that application of SW-FAM sequences results in considerable improvement of the signal-to-noise ratio, which directly translates into time saving when acquisition of NMR spectra of spin-7/2 nuclei is required, as in the studies in Refs. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”