The electronic conductivity mechanism in Bi-Sr-Ca-Cu-O glass-ceramics

The results of electrical conductivity measurements in Bi2O3-SrO-CaO-CuO glass-ceramics are reported. It is shown that a sharp increase in the conductivity observed at 460°C is attributed to the crystallization of the Bi2Sr2CuO6 (Bi-2201) superconducting phase in the glass matrix. The mechanism of electrical conductivity in this glass-ceramic can be explained as a result of discontinuous metallic structures of the Bi-2201 phase which appear in the glass matrix during annealing. The low-temperature conductivity obeys the law [sgrave](T) = [sgrave]0exp[(-T 0 /T)n] with n changing from 1/4 to 1/2 with decrease in the temperature. This cross-over is related to a granular structure in which a parabolic Coulomb gap exists in the density of states N(E) near E F. We also show that the superconductivity effect should be taken into account for T−1/2 conductivity behaviour. It is shown that the Bi-Sr-Ca-Cu-O glass after a very short heat treatment at 820°C exhibits the superconducting transition. In the normal state the conductivity is typical for granular metals and the activation energy continuously decreases with decreasing temperature.