Is the n-type conductivity in some Bi-doped chalcogenide glasses controlled by percolation?

The compositional dependences of the resistivity (ρ{variant}) of Ge₂₀Bi_xSe_80-x and Ge₂₀Bi_xS_80-x glasses (0 ≤ x ≤ 15) have been measured and interpreted from the point of view of percolation-controlled conductivity in these materials. The results of the simulation of the experimental compositional dependences of ρ{variant} show that a transition from p to n-type conductivity most probably occurs in the vicinity of a percolation threshold. In homogeneous transport therefore seems to be typical of these glasses, a feature supported, at least for Ge₂₀Bi_xS_80-x, by the observation of two softening temperatures.