Revealing the fine features of charge transport mechanism in ionic glass-forming liquids by dielectric spectroscopy

By examining the fine features of the dielectric spectra of a variety of ionic glass-forming materials, including ionic liquids and poly(ionic liquids), we show that the derivative of their real permittivity progressively broadens on the low-frequency side when the glass transition is approached from above. This phenomenon, ubiquitous and yet difficult to ascertain in the widely-used conductivity or modulus representation, is reminiscent of the spectrum broadening in supercooled dipolar liquids. Our finding provides direct evidence of heterogenous dynamics in ac conduction of ionic glasses and calls for a reconsideration of the classical models that predict a steep, Debye dispersion at low frequencies.