Lattice dynamical studies of ternary superionic conductors Ag3SX (X=I, Br)

A de Launey angular force model has been applied to study the phonon disper sion in three symmetric directions of ternary superionic conductor Ag3SX (X = I, Pr) by assuming them to be ideal perovskite type structure. A lattice dynamical calculation reasonably interprets the dominance of mobile ions i n highest frequency mode. The short-range (f(S)) acid long-range (f(L)) for ces in Ag3SX (X = I, Br) for a high frequency band are estimated near the t ransition temperature T-c and below 300 K. The f(L) values in both the cond uctors show an increase with T above T-c whereas the values of f(s) decreas e with T. The temperature dependence of f(L) and f(S) are explained satisfa ctorily from this calculation.