Activation energy for dc conductivity in dehydrated alkali metal-exchanged montmorillonites: experimental results and model

The ac conductivity of a series of dehydrated alkali metal-exchanged (Li+, Na+, K+, Rb+, and Cs+) montmorillonites has been measured at different temperatures, and the activation energy for dc conduction determined in each alkali metal-exchanged sample. The activation energy exhibits a remarkable minimum in the K+-montmorillonites. This behaviour can be explained using a simplified ionic bond model based on the Density Functional Theory and on the Electronegativity Equalization Method. It is shown that the exchangeable alkali metal–montmorillonite bond results from a shared contribution of electrostatic, covalent, and polarization energies.