Hopping Conduction in Glassy and Crystallized Bi-Sr-Ca-Cu-O System

Abstract

The results of electrical conductivity measurements in Bi–Sr–Ca–Cu–O glasses and partly crystallized glasses were reported. In glassy state the DC conductivity has been measured in the temperature range between 300 and 780 K. The small polaron hopping between copper ions in a different valency state Cu1+–Cu2+ is found to be the most appropriate conduction mechanism in this glass. A sharp increase in the conductivity is observed at 733 K, which agrees fairly well with the temperature of crystallization of the 2201 superconducting phase. The mean size of 2201 crystalline grains were evaluated from the broadening of XRD peaks. The mechanism of electrical conductivity in crystallized glasses can be explained as a result discontinuous metallic structures of the 2201 phase which appears in the glass matrix during annealing. For these samples, DC conductivity was measured from 5 K to room temperature. The conductivity exhibits a T—1/2 dependence between 4 K and about 40 K and a T—1/4 dependence above 40 K. This behaviour is discussed in the light of theoretical models that explain the T—1/2 dependence of conductivity in granular systems.