Electrochemical properties of Ag₅Te₂Cl _0.8Br_0.2, a representative of the solid solutions Ag ₅Te₂Cl_1-xBr_x

Impedance spectroscopic investigations of Ag₅Te ₂Cl_0.8Br_0.2, a selected representative of the solid solutions Ag₅Te₂Cl_1-xBr_x with x = 0-1, proved the mixed-conducting property of this class of materials. Two polymorphs are realized in the temperature range of 309 to 410 K, the monoclinic β-phase (space group P2₁/n) and the tetragonal α-phase (space group 14/mcm) with an order-disorder phase transition temperature of 336 K (DSC). A sharp increase of the total and ionic conductivity can be observed at 337 K, in good accordance with the phase transition temperature. The electronic conductivity exceeds the ionic conductivity by approximately one order of magnitude over a wide range of temperature. Conductivities are σ_ion = 6.9 × 10^-5 (309 K) and σ_tot = 4.80 × 10^-4 Ω^-1 cm^-1 (310 K) for β-Ag₅Te₂Cl _0.8Br_0.2 and σ_ion = 1.6 × 10 ^-2 (395 K) and σ_tot = 1.73 × 10^-1 Ω^-1 cm^-1 (394 K) for α-Ag₅Te ₂Cl_0.8Br_0.2.