Crystal-Field-Fluctuation Dynamics in Superionic Conductors: EPR ofMn2+in PbF2

EPR is used to probe the ion-motion spectral density in a superionic conductor. ${\mathrm{Mn}}^{2+}$ EPR in Pb${\mathrm{F}}_2$ shows a vacancy-diffusion-induced collapse of the ${\mathrm{F}}^{19}$-transferred hfs above 400 K. At higher temperatures, a linewidth dependence on $m^{\mathrm{}\left(55\right)\mathrm{}}$ of each ${\mathrm{Mn}}^{55}$ hfs component appears which we attribute to the dynamic modulation of the crystalline field resulting from the coupling between diffusive excitations of the "ionic liquid" and acoustic phonons.