Density Scaling in Ionic Glass Formers Controlled by Grotthuss Conduction

We present investigations of the charge transport in an ionic glass-former carvedilol dihydrogen phosphate (CP) at various T- P- V thermodynamic conditions in terms of density scaling concept. The studied material was found to reveal superprotonic properties both at ambient and elevated pressure, as proved by the Walden rule. Surprisingly, from the isobaric conductivity data, the relaxation times τ_σ presented in volume formalism showed no visual evidence of a liquid-glass transition. The different behavior of relaxation dynamics above and below T_g was only revealed from the analysis of log τ_σ( V_sp) data at isochronal conditions. The τ_σ experimental data of CP plotted as a function of ( TV^γ)^-1 satisfy the thermodynamic scaling criterion in the supercooled liquid as well as in the amorphous regime, however with a different γ coefficient (γ^SL = 1.12; γ^G = 0.48). Nevertheless, by introducing the idea of fictive temperature T_f, the transport properties of glassy and supercooled Grotthuss-type conductors measured at various T- P points obey the universal scaling with the use of a single γ parameter.