Reinvestigation of ionic motion in amorphous materials: A power law approach to the a.c. conductivity. Progress report

The motion of mobile ions in glassy materials produces a dielectric response that is characteristically non-Debye. This deviation from ideal Debye behavior is evidenced both in the a.c. conductivity, {sigma}(f), which increases anomalously as a power law of the form {sigma}(f) = {sigma}{sub 0}(1+(f/f{sub 0}){sup n}), and in the electric modulus which is better described by a stretched-exponential relaxation of the form {phi}(t) = exp({minus}(t/{tau}){sup {beta}}). The authors have examined the dielectric response of sodium germanate glasses over a wide composition range. In accordance with other studies, they observed substantial narrowing of the electric modulus with decreasing alkali content. However, no changes were evident in the power law response of the a.c. conductivity, and {sigma}(f) could be scaled to a common response curve at all compositions. This result clearly rules out inter-ionic interactions as a source for the non-Debye relaxation. The authors extended the study of sodium germanates to examine also the power law dynamics in the mixed alkali (MA) glass