An interionic potential was developed in order to investigate Li ion motion in the rigid framework of PO4 tetrahedra and ZrO6 octahedra, of this Nasicon-type superionic conductor, by fitting low-temperature X-ray structure and conductivity data at 700K. Molecular dynamics simulations were carried out by using this potential function. A detailed analysis of the molecular dynamics trajectories suggested that the proposed interionic potential could predict the properties; in good agreement with known X-ray, nuclear magnetic resonance, calorimetric, conductivity and other data. The transition from normal to superionic conduction took place between 550 and 600K, and was accompanied by a peak in the constant-volume specific heat. This suggested a higher-order transition, as well as the migration of Li ions from 6b (site 1) to 18e (site 2). The activation energy and migration path for Li ions moving from sites 1 to 2 were in good agreement with experiment. The density contours surrounding sites 1 and 2, which revealed the exact geometry of the void space around the sites, were in excellent qualitative agreement with thermal ellipsoid parameters obtained by X-ray diffraction. The frequencies of vibration of Li ions in the two sites were found to depend strongly upon the geometry of the void space at these sites; as dictated by the potential energy surface.

Lithium Ion Motion in LiZr2(PO4)3. P.P.Kumar, S.Yashonath: Journal of Physical Chemistry B, 2001, 105[29], 6785-91