Dielectric response of Na β-alumina: Evidence for a "glass transition"
Abstract
Electrical modulus (M'') data for melt-grown Na β-alumina between 92 and 151 K is fitted in terms of the fractional-exponential-decay formalism with a fractional exponent n. Above 120 K the exponent n decreases rapidly with increasing temperature, whereas the M'' peak frequency shifts with temperature as predicted by the Williams-Landel-Ferry relation. The behavior of n and M'' is similar to that observed for glasses near their glass transition, which suggests that Na β-alumina undergoes a "glass transition" near 120 K. It is also shown that the recent low-frequency-response model of Ngai yields the observed n(T), M''(ω,T) behavior and leads to the determination of the microscopic activation energy for Na+ -ion motion of 0.059 eV.
- Publication:
-
Physical Review B
- Pub Date:
- May 1983
- DOI:
- 10.1103/PhysRevB.27.6031
- Bibcode:
- 1983PhRvB..27.6031N