V-51 AND NB-93 HIGH-RESOLUTION NMR-STUDY OF NBVO5

NbVO5 is characterized by V-51 and Nb-93 NMR resonance frequencies strongly upfield shifted when compared to those in model compounds V2O5 and LiNbO3. The chemical shift anisotropy dominates the V-51 observed spectrum in a magnetic field of 11.7 T. The asymmetry parameter eta-c is 0.2 and the quadrupole coupling constant is relatively small (1 MHz). The quadrupolar Hamiltonian overwhelmingly dominates the Nb-93 spectrum (eta-q = 0.9) and the quadrupole coupling constant is huge (16.5 MHz). In agreement with the structure obtained from the x-ray powder diagram the isotropic chemical shift of V-51 suggests that NbVO5 is indeed an orthovanadate. Interestingly, in NbVO5 the isotropic chemical shift of Nb-93 reveals a better shielding of the Nb-93 nucleus and a lower electric field gradient than in LiNbO3. Nb octahedra in NbVO5 are sharing corners whereas they share edges in LiNbO3.