Conductivity percolation transition of Ag (Ge0.25Se0.75)100− glasses

Abstract The ionic conductivity of several chalcogenide glasses increases abruptly with mobile ion addition from values typical of insulating materials (10 −16 –10 −14 Ω −1 cm −1 ) to values of fast ionic conductors (10 −7 –10 −1 Ω −1 cm −1 ). This change is produced in a limited concentration range pointing to a percolation process. In a previous work [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259] the transition from semiconductor to fast ionic conductor of Ag x (Ge 0.25 Se 0.75 ) 100− x glasses was detected at x ∗ ≅ 10 at.% in the form of a steep change in the conductivity. Ag x (Ge 0.25 Se 0.75 ) 100− x glasses with x ⩽ 25 at.%, prepared by a melt quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz–2 MHz at different temperatures, T , from room temperature to 363 K and by DC measurements at room temperature. The conductivity of the glasses, σ , was obtained as a function of silver concentration and temperature. For x ⩾ 10 at.% our results are in agreement with those reported by Kawasaki et al. [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259]. The percolation transition was observed in the range 7 ⩽ x ⩽ 8. The temperature dependence of the ionic conductivity follows an Arrhenius type equation σ = ( σ o / T ) · exp(− E σ / kT ). The activation energy of the ionic conductivity, E σ , and the pre-exponential term, σ o , are calculated. The results are discussed in connection with other chalcogenide and chalcohalide systems and linked with the glass structures.