Universalities of conductivity spectra in protonic conductors

Frequency dependencies of conductivity σ′(ω), [σ(ω) = σ′(ω) – iσ″(ω)] of the most common disordered ion conductors show a lot of similar properties. Among the most important features belong universal properties of conductivity spectra, so called first and second universalities. The first universality is a characteristic frequency dependence of the real part of electric conductivity and refers to thermally activated hopping mechanism of ionic movement through solid state. The second universality is the effect observed at sufficiently low temperatures or high frequencies. Translational movements of ions through solid state do not contribute to dielectric loss. Because of this, the second universality is often called Nearly Constant Loss (NCL) effect. Such universalities are commonly observed in many various polymers and glasses, despite significant differences in structure and type of ionic charge carriers in those materials.

Recently [1–3] we have shown that similar universal conductivity response can also be observed in crystalline, hydrogen bonded proton conductors such as organic conductors, build of heterocyclic molecules (i.e. imidazole) with dicarboxylic acid. This contribution aims to prove that the same effect exist also in crystalline proton conductors, such as (NH4)3H(SO4)2 or (NH4)3H(SeO4)2, which undergoes phase transition from low conducting to high conducting phase. Although the mechanism and dynamics of proton migration through the lattice changes significantly at the transition temperature Ts, it does not influence the conductivity frequency response.

[1] Ławniczak et al., Solid State Ionics 225 (2012) 268.
[2] M. Zdanowska-Frączek et al., Solid State Ionics 227 (2013) 40.
[3] P. Ławniczak et al., accepted in Solid State Ionics.