Systematic studies on Bi-Sr-Ca-Cu-O glasses and glass ceramics

Abstract

Bi-Sr-Ca-Cu-O glasses and glass ceramics of various compositions have been synthesised. The glass transition temperature varies from 396 to 422 degrees C depending on the glass composition. DC electrical conductivity, measurements on these glasses show a sharp change in slope of the plot of logarithm of conductivity against reciprocal of temperature at a characteristic temperature that depends on the glass composition. The conductivity data divide into two distinct temperature regions: the conductivity mechanism at low temperatures has a much lower activation energy than that at higher temperatures. The results are discussed in terms of the small polaron theory. Electrical conductivity measurements on the bulk glass ceramics show that the samples of Bi4Sr3Ca3Cu4Ox, Bi4Sr3Ca3Cu6Ox, Bi2Sr2Ca2Cu3Ox and Bi4Sr2Ca4Cu6Ox compositions show superconductivity with Tc(onset) above liquid nitrogen temperature when heat treated at 820 degrees C for 3, 9, 12 and 24 h respectively. The Bi4Sr3Ca3Cu4Ox bulk superconducting glass ceramic is an almost single-phase material with preferred orientation such as the c axis is perpendicular to the sample surface. The Bi2Sr2Ca2Cu3Ox glass ceramic has higher Tc(onset) and thus shows the possibility of obtaining a superconducting material with Tc(zero) of 110 K. The possible reasons for the low Tc(zero) observed in these glass ceramics and the methods for its enhancement are discussed.