Evidence of a low-temperature dipolar glass state in polycrystalline ( NH_4 ) _3 H( SO_4 ) _2

Detailed dielectric measurements are reported for polycrystalline ( NH_4 ) _3 H( SO_4 ) _2 at temperatures 10 K < T < 100 K and frequencies 20 Hz < ν < 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 τ _0 = 3.5× 10^-13 s, E = 50 K^γ , and γ = 0.37 .