The Existence of the Order Phase in Superionic Conductor Ag3SI

The ordered phase concerning the Ag distribution of superionic conductor Ag 3 SI was discovered below 157 K. The transition heat and the entropy change were measured to be 0.23 kcal/mol and 1.44 cal/mol.deg. respectively. The crystal structure of the newly found γ-phase was studied by X-ray diffraction method. The space group of the γ-phase may be C 4 3 –R3 and the transition to the β-phase is of first order but is very close to the second order one.