Heterogeneous and homogeneous diffusivity in an ion-conducting glass

The nature of ion diffusivity in the vitreous conductor 2Ca(NO3)(2) . 3KNO( 3) (CKN) was studied by nonresonant dielectric hole burning. Spectral holes in the electric field relaxation are probed subsequent to a high electric sinusoidal burn field. For sufficiently high pump frequencies we are able t o induce spectrally selective modifications in the relaxation of the electr ic modulus, indicating that ionic diffusivity is a spatially varying quanti ty in glassy CKN. Homogeneous behavior occurs in the regime of low pump fre quencies, in which the resistivity approaches its steady state value. Thus, longer-ranged ionic motions lead to a spatial averaging over the heterogen eity of local ion diffusivities.