TEMPERATURE-DEPENDENCE OF THE DYNAMICAL EFFECTIVE CHARGE IN AG3SI

The temperature dependence of the phonon frequencies and effective cha rges in the superionic material Ag3SI is reported. It was found that t he effective change decreases with temperature T in the gamma-phase, j umps at the gamma-beta phase transition point T=157 K, remains almost insensitive to T until immediately above the beta-alpha phase transiti on at T=519 K, and increases rapidly with T in the alpha-phase. The be havior has been explained based on a model in which the basic process is the local fluctuation of the chemical bond.