The frequency dispersion curves of electrical conductivity as a function of temperature, sigma(omega, T), were obtained from 5 Hz to 13 MHz in the two-phase mixture beta-AgI solid solution (ss)+AgBr ss (at the concentration 20 mol% AgBr which has the maximum do conductivity) and pure beta-AgI in the temperature range 278-333 K. We found for this concentration of AgBr that the do conductivity, 6o, is 55 times higher than that of (3-AgI at 302 K; with a corresponding lower activation energy, E-sigma, for the first material. Moreover, the calculated ac conductivity parameters also reflect the effects of bromine on promoting silver ion. In fact, the bromine mixture also shows lower activation energy for the hopping rate, E. as well as higher values of the attempt frequency for ionic migration, omega(0), and the Kohlrausch parameter, beta, than those corresponding parameters for beta-AgI. The results are discussed in terms of the effects of lattice polarizability on ion motion. (C) 2003 Elsevier Science B.V All rights reserved.