It was recalled that this material became superionic near to 388K as the crystal structure changed from tetragonal to hexagonal. Near to 445K, the Ag2CdI4 was replaced by an equilibrium mixture of α-AgI and CdI2. At each of these phase transitions, the ionic conductivity increased by at least an order of magnitude. The substitution of Cu+ for Ag+ in Ag2CdI4 was accompanied by a slight increase in the room-temperature conductivity. This was the result of increased crystalline defects or of an increased Cu+-free volume in the tetragonal lattice. Also, Cu substitution appeared to stabilize the high-temperature hexagonal structure to well above 445K.

Ionic Conductivity in Cu-Substituted Ag2CdI4. R.B.Beeken, J.C.Faludi, W.M.Schreier, J.M.Tritz: Solid State Ionics, 2002, 154-155, 719-22