Magnetization and resistivity ofBi4Ca3Sr3Cu4O16-type materials having two superconductivity onset temperatures

Abstract

Annealing ${\mathrm{Bi}}_4$ ${\mathrm{Ca}}_3$ ${\mathrm{Sr}}_3$ ${\mathrm{Cu}}_4$ ${\mathrm{O}}_{16}$ in flowing oxygen at ∼885°C results in a material with two superconducting onsets, at about 85 and about 115 K. Magnetization data suggest that such materials consist of two kinds of regions in contact, even though only one phase is apparent in x-ray spectra. Resistivity data above the 85-K transition contain contributions from thermodynamic fluctuations and suggest that pair-breaking effects are small in the annealed materials.