Dielectric permittivity, ac conductivity and phase transition in hydroxyl ammonium sulfate

Abstract

The complex dielectric permittivity (ε*=ε′−jε″) and ac conductivity σ (ω, T) as a function of temperature (90–375 K) and frequency (0.4 kHz to ≈100 kHz) were measured in this work for polycrystalline samples of hydroxyl ammonium sulfate, (NH3OH)2SO4. The measured electrical parameters revealed the existence of a structural phase transition at T≈312 K, which was further confirmed by a differential thermal analysis thermogram, where a clear endothermic peak centered at ≈312 K is observed. Regarding the charge transport mechanism, it is likely that the behavior of frequency-dependent conductivity follows the universal dynamic response σ (ω,T)=A(T) ωs(T). Moreover, the temperature dependence of the frequency exponent s (0⩽s⩽1) suggests the quantum mechanical tunneling model to be the most likely one that describes the electrical transport mechanism. The data correlate with the crystal structure and the hydrogen-bonding system.