A DFT-based model to the interpretation of DC conductivity in transition metals doped zinc phosphate glass

Ternary zinc-sodium-phosphate glasses doped with transition metal of the composition Na₂MxZn_1−xP₂O₇ (x = 0,1,2 and 5 mol %) (where M = Ni, Cu and Co) were prepared by the traditional quenching method. The ac conductivity measurements at different temperatures for the prepared glasses have been investigated, and the activation energy for dc conduction has been determined in each transition metal doped sample. The results showed that the evolution of the activation energy of the conductivity depends on the nature of the dopant ions. A model based on formal density functional theory concept in which the electrical charge exchanged between the transition-metal cations and the surrounding material surface is proposed. The outcome is a "simplified" formula which allows us to explain the evolution of the ionic dc conductivity activation energy as a function of the doped ion in interaction with the cation and the surface. (author)