SOME PROPERTIES OF HONEYCOMB-TYPE BI1.6PB0.4SR2CA3CU4OY SUPERCONDUCTORS

A Bi-based superconductor of nominal composition Bi1.6Pb0.4Sr2Ca3Cu4Oy was prepared using Bi2O3, PbO, SrCO3, CaO and CuO powders and liquid ammonium nitrate as solvent and homogenizer. For comparison, another s uperconductor with nominal composition Bi1.8Pb0.2Sr2Ca2Cu3Ox was obtai ned using the same method and conditions. It was observed that the cer amic has a honeycomb granular structure, a transition temperature of 1 10 K, an increased thermal expansion coefficient (8.7x10(-6) K-1) and a fourfold higher critical current density (25 A cm(-2)). The volume o f the sample increased during annealing (for 100 h at 845 degrees C). The phases existing in this new type superconductor were determined. T he composition and temperature dependences of phase transition charact eristics, resistivity and inductance changes were investigated. The he ight of the energy barrier separating the metastable local superconduc ting phase and the normal metallic phase was found to be 0.34 eV in th e temperature interval 110 K<T<130 K from rho(T) measurements.