Proton conductivity and ferroelectric phase transition in hydrogen-bonded ferroelectric NH4IO3

Abstract

We report on the ac dielectric permittivity (ε) and the electric conductivity (σω), as function of the temperature 300 K < T< 400 K and frequency 0.5–100 kHz for polycrystalline samples of hydrogen-bonded ferroelectric ammonium iodate, NH4IO3. The main feature of our measured parameters is that, the compound undergoes a ferroelectric phase transition of an improper character, at (368 ± 1)K from a high temperature paraelectric phase I (Pm21 b) to a low temperature ferroelectric phase II (Pc21n). The electric conduction seems to be protonic. The frequency dependent conductivity has a linear response following the universal power law (σ( ω ) = A(T)ω s (T)). The temperature dependence of the frequency exponent s suggests the existence of two types of conduction mechanisms.