Polymerized Complex Synthesis of the Modulation-free (Bi, Pb)₂Sr₂(Ca, R)Cu₂O_8+d(R: Rare Earth=Y)

Abstract

High-purity ceramic samples of the modulation-free Bi_2-xPb_xSr₂Ca_1-yY_yCu₂O_z with a wide range of composition (x=(l+y)/2±0.2, 0.25≤y≤0.8) have been prepared by the polymerized complex method. The method is based on the formation of a polymer complex which is obtained through polyesterfication between metal citrate complexes and ethylene glycol. This method yielded almost homogeneous x=0.8 materials with Y compositions of y=0.2, 0.6 and 0.8 through relatively short sintering periods of 32 hours. The corresponding X-ray diffraction and Raman scattering analyses have shown that the materials are virtually of single phase with only minor traces of Sr_2.5Bi_0.5Pb₃Ca₂CuO_z (< 1 %). The lattice parameters a and b increase, while the c-axis value decreases with increasing Y content, y. Complex magnetic susceptibility measurements have confirmed the presence of a single bulk Bi2212 phase. For Bi_1.2Pb_0.8Sr₂Ca_0.8Y_0.2Cu₂O_z, the onset temperature of superconducting transition Tc was 89.5 K and the transition width (10-90 %) of full diamagnetism was 6.4 K for the measuring field of 100 mOe. The variation of Tc with Y content in the modulation-free Bi2212 phase was similar with that observed in the modulated Bi₂Sr₂Ca_1-yY_yCu₂O_z.