Sodium-ion self-diffusion in P2(γ)-NaxCoO2 was studied using a single crystal as an electrode. Mass transport and thermodynamic properties of Na ions were measured by the potentiostatic intermittent titration technique on a single-crystal electrode with greater accuracy under well-defined diffusion geometry. Excluding the significantly slower diffusion behavior near particular Na ordered phases, average diffusion coefficients DNa were extracted to be 1.2 x 10−7cm2/s for x>0.5 and 4.1 x 10−8cm2/s for x<0.5, respectively. The existence of stable phases with special Naordering of x~0.25, 0.33, 0.43, 0.5, 0.55 and 0.71 were verified by either the maximum or diverging signature of the x-dependent self-diffusion coefficients.

Sodium-Ion Diffusion and Ordering in Single-Crystal P2-NaxCoO2. G.J.Shu, F.C.Chou: Physical Review B, 2008, 78[5], 052101 (4pp)