Particle Size Dependence of the Electrical Conductivity of NaCl

The ac and dc conductivities of single‐crystal and polycrystalline NaCl were measured as a function of both temperature and particle size. The ac conductivity results for single‐crystal NaCl agreed well with the literature: intrinsic activation energy = 1.86 ev; extrinsic, impurity‐controlled range = 0.74 ev; extrinsic, association range = 1.16 ev; and the intrinsic‐extrinsic knee in the curve was at 10 3 / T ∼ 1.4°K −1 and σ 0 ∼ 6 × 10 −8 ohm −1 cm −1 . In the intrinsic range, however, the total conductivity (σ 0 ) was the sum of two ionic contributions: a steady state, nonblocked contribution (σ θ and a blocked contribution (σ 0 —σ θ ). The activation energy for the dc steady state conductivity was 1.6 ev. When the extrinsic, impurity‐controlled contribution to the total conductivity was made insignificant by anion doping, the same 1.6 ev was the activation energy for the intrinsic ac conductivity at low temperatures. The data for the polycrystalline samples showed that ac conductivity increased inversely with particle size and dc steady state conductivity increased only slightly, if any, with decreasing particle size. It is postulated that the steady state conductivity is the result of the nonblocked ionic transport of sodium ions and that the ac portion of the total conductivity is due to the movement of chlorine ions which are blocked, giving rise to the polarization phenomenon. The increase in the ac conductivity with decreasing particle size is correlated with the enhanced movement of Cl − in the subgrain boundary region, as has been previously shown by diffusion measurements.