Modeling Ionic Conductivity in Nasicon Structures

Considering only the structure of oxygen lattice and employing bond valence equations, the conduction geometry and the activation energy of Na+ motion in Nasicons are modeled. This is performed by calculating the valence sum m(x, y, z) for a grid of points inside the oxygen lattice, then by following with iterative procedures the pathway with lowest relative m(x, y, z) values, starting from a specified position and initial direction. After a certain trajectory the Na+ ion will reach a second position in the lattice, which will usually correspond to a known crystallographic position. Different rhombohedral and monoclinic Nasicons are examined, enabling us to verify some the ionic movement. Structural parameters governing conduction are described, based on the distortions of real structures from an idealized (archetype) Nasicon structure, in turn modeled by bond valence equations.