Ferroelectric phase transition in the superionic conductor Ag26I18W4O16

An analysis of the dielectric measurements for the ferroelectric phase transition in the superionic conductor Ag26I18W4O16 is reported. The transition is interpreted as being slightly first order, with a hysteresis region less than 2.5 °K in width. The system obeys Curie–Weiss dependences in both phases, with the dielectric constant satisfying the equation in the paraelectric phase and in the ferroelectric phase. The ferroelectric transition is of the order–disorder-type and involves mobile silver ions. The frequency dependence of ionic conductivity has been measured in the high temperature phase. From 0.5 to 10.0 kHz it satisfies σ (ω) proportional to ω in contrast to the ω2 dependence predicted by Lines.