Nuclear magnetic resonance quadrupolar parameters and short range order indisordered ionic fluorides

Information on both radial and angular atomic coordinations is provided by the quadrupole interaction between the quadrupole moment of the atomic nucl ei and the electric field gradients (EFGs) originating from the distributio n of electric charges around the nuclei. Ga-69 and Ga-71 are quadrupolar nu clei active in NMR. Their spectra are recorded in amorphous GaF3 which may be considered as a model compound for disordered fluorides with fluorine co rner sharing octahedra. An unique and continuous quadrupolar parameter Czjz ek distribution allows us to simulate the experimental spectra. The measure d chemical shifts indicate that the Ga3+ ions are at the centre of(GaF6)(3- ) octahedra in the amorphous GaF3 phase. A polarizable point charge model is used to explain NMR quadrupolar paramet ers which are related to the electric field gradients at the Ga site. Latti ce summations are performed in the direct space over spherical volumes. Ato mic position sets generated by molecular dynamics are shown to give quadrup olar parameter distributions which look like Czjzek ones whatever the EFG c alculation approximations. Provided the polarizabilities are adjusted, they allow us to reconstruct the experimental NMR spectra which correspond in a ny case to slightly distorted (GaF6)(3-) octahedra. The present approach ma y be applied to any ionic disordered compound which contains quadrupolar nu clei and used to quantify short range order around such nuclei.