Li doping to the 2212 phase in the Bi-Sr-Ca-Cu-O system

The effects of Li doping on the formation process of the 2212 phase in the Bi-Sr-Ca-Cu-O system, and its structural and superconducting features were studied. Samples with nominal compositions of Bi : Sr: Ca: Cu: Li = 2: 1.5: 1.5: 2: x where 0 ≤ x ≤ 0.6 were heated in air at temperatures ranging between 560°C and 850°C. Li doping greatly promoted the formation of the 2212 phase; the monophasic samples were rapidly obtained for x ≤ 0.4 by firing even at 730°C, which is about 100°C lower than that of the non-doped 2212 phase. A newly found oxide phase containing Li, which was formed below 710°C, is considered to play an important role as a precursor to accelerate the formation of the 2212 phase. The Li content in the monophasic samples determined by ICP analysis decreased to about a half of the nominal composition due to partial Li escape during heating. Monophasic composition range of the Li-doped 2212 phase was 0 ≤ y ≤ 0.19 as Bi₂Sr_1.5Ca_1.5Cu₂Li_yO _z. Increase in both lattice parameter c and oxygen content z with increasing Li content y in the 2212 phase was accompanied with a rise of T_c up to 90 K.