Influence of the heat treatment profiles on the development of highly textured Ag/Bi2212 monofilamentary tapes

The use of superconducting ceramics, with higher critical temperatures and higher operation temperatures, leads to economy of cryogenic liquids and systems. One of the largest problems in the practical use of superconducting ceramics is the intrinsic anisotropy of the critical currents. The present work describes a study of the texturing process in Ag/Bi2212 monofilamentary tapes, permitting the optimized choice of the heat treatment profiles to obtain superconducting phases close to the stoichiometric, with high texturing and high critical current densities J_c. The samples of Ag/Bi2212 tapes were obtained using the powder-in-tube (PIT) process with partial melting, treated at different maximum temperatures and with fixed cooling rate and isotherm at low temperature under oxygen flow at atmospheric pressure. The microstructural, electrical and superconducting characterization showed that the Ag/Bi2212 tapes submitted to different heat treatment profiles had significant improvements on the texturing and on the superconducting and microstructural characteristics and properties. The tapes treated with the maximum temperature of 890 °C for only 10 minutes followed by a cooling rate of −5 °C/h and 5 hours at the 830 °C isotherm presented best critical current densities of 7.5 × 10⁴ A/cm², at 4.2 K and 5 T; and 1.4 × 10⁵ A/cm², at 4.2 K and 0 T. This very short step at high temperature is extremely important for magnet development and applications.