Solid-state synthesis of Pb2Sr2CaCu 3-ySx and conducting properties

Abstract

In this study complete substitution of O by S in Pb-Sr-Ca-Cu-O superconducting system that has the general formula Pb2Sr 2MCu3O8+8 (M = Y, Ca) had been attempted. For this purpose, solid-gas reactions of solid mixture, PbO, Sr(NO3) 2, CaO and CuO with a sulfidizing gas consisted of COS, CS 2, CO, CO2 and sulfur vapour were performed. For M, only Ca was used. The obtained product Pb2Sr2CaCu 3-yx, was characterized by XRD, IR, SEM, EDX, conductivity measurements and chemical analysis. X-Ray powder diffraction pattern of Pb 2Sr2CaCu3-ySx was found to be very similar to PbS diffraction pattern reported in JCPDS Card No.5-592 which has a rock salt structure with a = 5.946 Å. Pb2Sr 2CaCu3-ySx was indexed in monoclinic system with the refined unit cell parameters of a = 5.947(8), b=5.941(3), c=11.98(1) Åand ?=90.19(9)°. Since 'c' unit cell dimension is almost twice of a and b, it is concluded that a superstructure formation had resulted which is common for complex sulfides. The absence of metal oxygen bands in IR and O bands in EDX spectra is taken to be the proof of the complete substitution of O by S by solid gas reactions. The conductivity of Pb2Sr 2CaCu3-ySx was measured by four-probe conductivity technique and was found to be metallic.