Structural changes which were produced during the triclinic-rhombohedral transition were analyzed by means of nuclear magnetic resonance spectroscopy. The reduction in symmetry produced a differentiation of 3 tetrahedral PO4 whose distortions were closely correlated with chemical shift anisotropies, as determined by means of 31P nuclear magnetic resonance. At the phase transition, the 31P chemical shift values changed according to the modification of the P-O-Hf angles, as determined by neutron diffraction. In the triclinic low-temperature phase, the location of Li along the conduction channels was confirmed by means of 7Li nuclear magnetic resonance spectroscopy. In these positions, a distorted but almost planar 4-fold coordination - with Li-O distances of about 0.21nm - explained the observed 7Li quadrupole coupling constants. In the rhombohedral high-temperature phase, the structural changes destabilized the Li coordination. In this case, the 7Li nuclear magnetic resonance spectra revealed an appreciable Li mobility. The significant delocalization of Li explained the strong increase in conductivity which was detected at the phase transition and made this one of the best Li-ion conductors.

Structural Changes at the Triclinic-Rhombohedral Transition and their Influence on the Li Mobility of the Fast-Ion Conductor LiHf2(PO4)3. M.A.Paris, J.Sanz: Physical Review B, 2000, 62[2], 810-7