Nano-scale γ-phase samples, with grain sizes of 7 to 9nm, were synthesized by quenching the molten halide in liquid N. The temperature dependence of the ionic conductivity was studied by means of complex impedance measurements. A plot of log[σT] versus 1/T revealed that it comprised 3 segments having differing slopes; with kinks at about 147 and 223C. The activation energies for the 3 segments were 0.40, 1.61 and 0.12eV, respectively. The curve revealed the occurrence of a continuous transition between 147C and 223C, instead of the break at 147C that occurred in normal AgI. This indicated a change from a first-order phase transition to a second-order one after quenching in liquid N. The room-temperature conductivity of nano-AgI was about 2 orders of magnitude higher than that of normal AgI. It was suggested that the ionic conduction of nano-AgI, at room temperature to 147C, at 147 to 223C, and at above 223C, was controlled respectively by grain boundaries and dislocations (which were introduced by quenching), by the formation and diffusion of Frenkel defects within grains and by the transport of quasi-liquid Ag ions. The second-order phase transition was attributed to lattice deformation and the formation of Frenkel defects.

Ionic Conductivity of Nano-Scale γ-AgI. Y.Wang, L.Huang, H.He, M.Li: Physica B, 2003, 325, 357-61