Upper critical field measurements using pulsed magnetic fields in Bi _1.6Pb_0.4Sr₂Ca₂Cu_2+xO _y (x=0.8, 1.2, 1.6)

Upper critical magnetic fields of the Bi_1.6Pb _0.4Sr₂Ca₂Cu_2+xO_y system with x=0.8, 1.2, 1.6 were measured by a magnetoresistance method using a pulsed magnetic field. The H_c2(0) are estimated to be 45.9, 218 and 64.9 T for x=0.8, 1.2, 1.6, respectively. H_c1(T) for each composition was determined from magnetisation curves. The superconducting parameters xi , kappa and lambda were derived from experimental data. X-ray diffraction patterns show that there is no obvious change in structure. It is suggested that the coordination number of Cu strongly influences the superconductivity.