Studies on Bi-Sr-Ca-Cu-O glasses and superconducting glass ceramics

Bi-Sr-Ca-Cu-O glasses and glass ceramics of various compositions were synthesised. The glass transition temperature varies from 396 to 422°C depending on the glass composition. The bulk glass ceramics of 4334, 4336, 2223 and 4246 compositions show superconductivity when the corresponding glass samples were heat-treated in air at 820°C for 3, 9, 12 and 24 h respectively. X-ray diffraction studies show that the superconducting phase present in all these compositions is Bi₂Sr₂Ca₁Cu₂O _x . The 4334 glass ceramic is almost a single-phase material with a preferred orientation such that thec axis is normal to the sample surface. The 2223 glass ceramic has a higherT _c (onset) than the other three compositions indicating the presence of highT _c phase (110K) also. ESR studies on the glass samples indicate the existence of Cu²⁺. The effect of heat treatment on ESR shows that the intensity of resonance decreases with increase in heat-treatment duration. This effect is more pronounced for the 4334 and 2223 compositions. The advantages of synthesizing superconducting materials by glass route are discussed in view of practical applications.