Relaxing Specific Heat in the Superionic Conductor RbAg4I5

An analysis is presented of data on sound absorption, specific heat, and ionic conductivity that demonstrates the existence, in the superionic conductor Rb${\mathrm{Ag}}_4$ ${\mathrm{I}}_5$, of internal degrees of freedom associated with the diffusing silver ions which may be characterized thermodynamically by a relaxing specific heat. It is pointed out that this simple analysis should provide useful information on ionic diffusive modes in other superionic conductors, particularly in regard to their coupling to lattice modes.