Percolation behavior of Ag in Ge16Sb12Se72 glassy matrix and its impact on corresponding ionic conductivity

In the present article, the silver diffusion behavior and its influence on ionic conduction have been studied from a series of glass samples Agx(Ge16Sb12Se72)100-x with 0 ≤ x ≤ 25. A non-linear evolution of the ionic conduction as a function of Ag concentration was found and attributed to a variation in the diffusion mechanism following the Ag rate. The glasses with Ag concentration lower than 5 at. % i.e. for Ag0.2 to Ag1, the Ag+ diffusion mainly occurs via a percolation mechanism, whereas for the Ag concentration from Ag5 up to Ag15, a hopping mechanism is prevailing. However, for Ag5 the diffusion occurs with mixed mechanism i.e. percolation + hopping way. For the Ag content higher than 15 at. % the diffusion occurs via a correlated walk and it was found that the repulsive nature between the Ag+ ions in the high concentrated sample due to much shorter distance does not show self-blocking nature. Additionally, the samples show a transition from electronic to ionic conductivity. From Raman analysis a correlation between the content of Ag and the type of GeSe4/2 tetrahedron, corner or edge-shared, which takes place in the structure, was evidenced. Finally, the results allow a better understanding of the mechanism of the Ag conduction in the glasses of the Ge-Sb-Se system using the random-walk (RW) model.