6Li{31P} Rotational-Echo, Double-Resonance Studies of Lithium Ion Site Dynamics in Li3V2(PO4)3

Abstract

Low-temperature 6Li{31P} rotational-echo, double-resonance (REDOR) measurements were used to study lithium mobility within each of the three Li sites in monoclinic Li3V2(PO4)3. Each of the Li ions was found to experience a different reduced dipolar coupling with the nearest 31P nucleus. Under fast magic-angle spinning (MAS) conditions (40 kHz), the three crystallographic 31P sites in Li3V2(PO4)3 were resolved. On the basis of the known Li−P internuclear distances, the 31P resonances were assigned by determining the degree of signal attenuation at each phosphorus site. The attenuation of the Li−P dipolar coupling, compared to simulations of the static case, was associated with rattling of the Li ions within the lattice. The relative mobility at each Li site is correlated with structural properties including the shortest Li−O contact within the void and bond valence calculations.