Low-temperature dielectric behavior of (NH4)3H(SO4)2 crystal

Dielectric investigations on (NH4)3H(SO4)2 single crystals below room temperature are reported. Dielectric dispersions are observed in the two regions of temperature above 200 K and below 70 K. Glass-like dielectric relaxations found in the dielectric constant and loss at T>200 K are considered due to reorientation of some dipoles derived by the random freezing of protons in the statically disordered hydrogen bonds. The dielectric loss at T<70 K is analyzed to result from the contribution of two Debye type relaxations. One of the corresponding relaxation times as a function of temperature shows a good fit to the modified Arrhenius equation at 29 K≤T≤70 K. The other one exhibits a critical slowing down on approaching a critical temperature, which seems to be closely associated with the λ-type phase transition at T∼67 K.