Evidence of a low-temperature dipolar glass state in polycrystalline ($\hbox {NH}_4$)$_3$H($\hbox {SO}_4$)$_2$

Abstract

Detailed dielectric measurements are reported for polycrystalline ($\hbox {NH}_4$)$_3$H($\hbox {SO}_4$)$_2$ at temperatures 10 K $< T <$ 100 K and frequencies 20 Hz $< \nu <$ 3 MHz. Instead of the ferroelectric phase transition expected at 63 K, a typical dipole glass transition was observed at around 60 K. The frequency dependence of the complex dielectric permeability at $T<$ 50 K was well described by a sum of two Cole–Cole functions. One of the two relaxators provides a background contribution to the dielectric dispersion. The most probable relaxation time for the main relaxator was best fitted to the modified Arrhenius law with $\tau _0 = 3.5\times 10^{-13}$ s, $E = 50$ $\hbox {K}^\gamma$, and $\gamma = 0.37$.