Advances in superconductivity and Co₃O₄ nanoparticles as flux pinning center in (Bi, Pb)-2223/Ag superconductor tapes

Many new superconducting materials have been discovered in recent years. This includes hydrogen sulfide which superconducts at 203 K under high pressure and Fe-As based materials. To this date the copper oxide-based materials remain as the highest transition temperature superconductor under normal pressure. In this paper we discuss the use of nano-sized particle as pinning center in the Ag-sheathed high temperature superconductor tapes to enhance the transport properties. When the size d of the pinning center is between the coherence length ξ and the penetration depth λ (ξ < d < λ), a stronger interaction between the pinning center and flux lines leading to higher transport critical current density, J_c can be expected. The effect of nanoparticle with size between the coherence length and the penetration depth i.e. ξ < d < λ, Co₃O₄ on superconductor tapes is discussed in this paper. Three types of Bi(Pb)-Sr-Ca-Cu-O starting materials namely from co-precipitation method without Co₃O₄ and with 30 nm and 50 nm Co₃O₄ addition have been prepared. The composition of the 30 nm and 50 nm Co₃O₄ added samples is (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀⁻(Co₃O₄)_0.02 and (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀⁻(Co₃O₄)_0.01, respectively. The tapes (∼2-3 cm long) were heated at 845°C for 100 and 150 h. All nanoparticles added tapes showed higher J_c compared to the non-added tapes. By comparing the current results with our previously reported results, the tapes with 30 nm Co₃O₄ sintered for 50 h showed the highest J_c at all temperatures. This work also showed that smaller magnetic nanoparticles enhanced J_c better than larger particles, A longer sintering time (> 50 h) degraded J_c.