Polymerized Complex Synthesis and the Raman Scattering of Bi_2.1Sr_1.9-xLa_xCuO_6+d

Abstract

High-purity polycrystalline samples of Bi_2.1Sr_1.9-xLa_xCuO_6+d with x=0-1 have been prepared by the polymerized complex method X-ray powder diffraction and complex magnetic susceptibility mesurements have shown that the samples are of a single-bulk Bi2201 phase without any impurity such as Bi₁₇Sr₁₆Cu₇O_y, CuO, Bi₂Sr₃Cu₂O_y, The dependence of the superconducting transition temperature T_c(onset) with increasing La content has a parabolic-like behavior with maximum T_c(onset)=16.6 K at x=0.3. We heve investigated the effect of La substitution for Sr on Raman spectra of Bi_2.1Sr_1.9-xLa_xCuO_6+d. The apical-oxygen phonon at-630cm^-1 softens by -20cm^-2 with increasing La content, when x goes from 0 to 1. This change can be interpreted in terms of the charge redistribution induced by decreasing the Cu and Bi valences with La doping.