First universality of conductivity spectra in superprotonic (NH₄)₃H(SO₄)₂ single crystal

Abstract

We present the frequency study of electric conductivity in the superprotonic single crystal in a wide temperature range covering the superprotonic phase I and the low conducting, ferroelastic phase II. The data below microwave frequencies are analyzed using the Summerfield scaling method to check for presence of the first universality. The scaled conductivity obtained from the raw experimental data plotted versus scaled frequency do not show the universality because it contains, in a low temperature range, steps related to relaxational dielectric contribution. The contribution, evidenced by a temperature study of frequency dependence of ε″, presumably comes from polar ammonia and therefore does not reflect properties of the hopping motion of mobile ions. To get rid of it, the conductivity is calculated using the impedance data obtained from the fitting procedure of the Nyquist plots. The resulting scaled ac conductivity plot forms a single curve in a wide temperature range. Thus, (NH4)3H(SO4)2 meets criteria for the first universality, despite the fact that it undergoes the structural, superionic phase transition in the temperature range studied.

Proton dynamics in superprotonic Rb3H(SeO4)2 crystal by broadband dielectric spectroscopy

“…Similar universal response was also observed in another superprotonic conductor (NH 4 ) 3 H(SO 4 ) 2 [28] that also undergoes a superionic phase transition. It shows that despite the existing differences in the structures, the scaling procedure and the universal frequency behaviour of the conductivity spectra is well applicable to the case of superprotonic conductors.…”

“…It is worth to notice that in the RHSe single crystal at higher frequencies, no additional contribution has been observed than that from the mobile protons. Additional conductivity contribution was, however, observed in (NH 4 ) 3 H(SO 4 ) 2 , caused by the polar ammonia groups [28]. However, in (NH 4 ) 3 H(SeO 4 ) 2 superprotonic conductor first universality of conductivity was not observed, due to existence of unique low conducting, ferroelastic phase III of symmetry (P 1) [56].…”

“…In the previous papers we have shown that both universalities of conductivity spectra can be observed in ordinary organic proton conductors, such as benzimidazolium azelate [25,26] and imidazolium malonate [27]. Recently, we have shown that the universal conductivity spectra behaviour is also similar for the superprotonic (NH 4 ) 3 H(SO 4 ) 2 single crystal, even when dielectric contribution from polar ammonia group influences the conductivity response [28].…”