Effects of TiO2 addition on the superconducting properties of Bi-Sr-Ca-Cu-O system

The effects of TiO2 addition in Bi2Sr2CaCu2O8Tiy (Bi-2212) with y = 0, 0.05, 0.10 and 0.15 and (Bi1.6Pb0.4)Sr1.6Ca2Cu2.8O10Tiy (Bi-2223) with y = 0, 0.10,0.20 and 0.40 are studied and compared. The samples have been investigated by powder X-ray diffraction (XRD), dc electrical resistance, critical current density (Jc) and scanning electron microscopy (SEM). The XRD patterns of the Bi2Sr2CaCu2O8Tiy materials showed the Bi-2212 as the dominant phase. In the TiO2 added samples (with x = 0.05 and 0.1), the c lattice parameter decreased slightly from the non-added sample showing the possibility of Ti incorporating into the crystal structure of the Bi-2212 phase. In the undoped (Bi1.6Pb0.4)Sr1.6Ca2Cu2.8O10 material, the XRD pattern showed the existence of mixed phases of Bi-2223 and Bi-2212. The TiO2 added Bi-2223 samples do not show any systematic variation in the c lattice parameter, indicating that Ti may not be incorporated into the Bi-2223 crystal structure. The Tc values in both systems decreased with the addition of TiO2. The critical current densities, Jc at 40 K in the Bi2Sr2CaCu2O8 system and at 77 K in the (Bi1.6Pb0.4)Sr1.6Ca2Cu2.8O10 system also decreased with the addition of TiO2. SEM micrographs of both systems showed a slight decrease in average grain size when TiO2 was added.