Terahertz electrodynamics of ionic transport in AgI-AgPO₃ glasses

Solid electrolytes are a promising class of materials for the next generation of batteries. However, their ionic conduction, an indicator of battery performance, is typically lower than that of liquid electrolytes. Understanding which microscopic parameters control ion motion is therefore crucial to engineer more efficient materials. Here, we investigate the ionic dynamics in the prototypical superionic glass AgI-AgPO₃ using time-domain terahertz spectroscopy (TDTS). By measuring the sample's transient response to a THz field, we extract the frequency-dependent complex conductivity, revealing the characteristic timescales and temperature dependence of the conduction. We observe a crossover from a bound-current response at low temperatures to activated ionic transport at high temperatures. These results provide new insight into the microscopic mechanisms of ionic transport in AgI-AgPO₃ and establish THz spectroscopy as a powerful probe of ion dynamics in glassy electrolytes, opening the door for future optical control of ionic conduction.