Raman Scattering of Ca-Substituted YBa₂Cu₃O_7-d Synthesized by Polymerized Complex Method

Abstract

Two types of Ca-substituted Y123 phase, (A) Y_1-0.75xBa_2-0.25xCa_xCu₃O_7-d and (B) Y_1-xCa_xBa₂Cu₃O_7-d have been prepared by a polymerized complex method X-ray powder diffraction and complex magnetic susceptibility measurements have shown that only type (A) is virtually of single phase without any impurities such as BaCuO₂ and Y₂BaCuO₅. The superconducting transition temperature T_c decreases from 92.2K (x=0) to 83.2K (x=0.2) with increasing x in (A). Furthermore, we investigated the effect of Ca-substitution on phonon Raman spectra of type (A) by using a micro-Raman spectrometer. Ba and 0(4) phonons are significantly shifted towards lower frequencies by 3cm^-1 and 4cm^-1, respectively, when x is increased from 0 to 0.2. A possible origin of the decrease in both T_c and Ba-0(4) layers phonon energies are discussed in terms of both hole doping in the CuO₂ planes and internal pressure induced by the Ca-substitution.