Open AccessPolarization relaxation in zinc oxide varistors from 77 K to 450 K
Author(s) -
R. W. Major,
A. Werner,
Cameron Wilson,
F. A. Modine
Publication year - 1994
Language(s) - English
Resource type - Reports
DOI - 10.2172/28384
Subject(s) - arrhenius equation , atmospheric temperature range , zinc , analytical chemistry (journal) , polarization (electrochemistry) , activation energy , oxide , materials science , relaxation (psychology) , condensed matter physics , exponent , chemistry , thermodynamics , physics , metallurgy , psychology , social psychology , linguistics , philosophy , chromatography
The time and temperature dependences of polarization currents are investigated to higher temperatures and with greater temperature resolution than has been reported previously for zinc oxide varistors. Arrhenius plots yield thermal activation energies near 140 and 8 meV, which are in reasonable agreement with values reported recently, as well as an additional thermally activated level at 0.66 eV, which emerges in the extension of the measurements to T > 300K. Conductance data in this higher temperature range for the same samples yield the nearly identical energy of 0.68 eV for the intergranular (Schottky) barrier height. The temperature dependence of the exponent m in the power-law expression for the current-time dependence I = I{sub o}t{sup {minus}m} was carefully examined and found to change twice from 0.5 to 1.0. The non-monotonic behavior of m with temperature is interpreted as due to resolution of the polarization currents from two different traps each of which makes the transition from diffusive to dispersive transport as temperature is lowered rather than, for example, a complicated distribution of relaxation times