%0 Journal Article
%T Investigation of Structural Formation of Starting Composition 2245 in the Bi-Pb-Sr-Ca-Cu-O System Superconductors
%A Ashoka Nukkanahalli Venkataswamy
%A George Thomas Chirayil
%A Srinivasan Kannaiyan
%J Journal of Solid State Physics
%D 2014
%R 10.1155/2014/716032
%X Structural formation of Bi1.65Pb0.35Sr2Ca4Cu5Oy (2245 phase) superconducting compound was investigated by preparing the sample in a new matrix route. The phases formed at different intervals of heat treatment are monitored by X-ray diffraction studies. Bi-2212 phase was found to be the predominant phase till 20 hours of sintering at 850¡ãC after which Bi-2223 phase was found to be the major phase. Traces of Ca2PbO4 were also noticed along with 2212 and 2223 phases. For the first time, the highest onset of 127£¿K with maximum superconducting volume fraction was observed for the sample sintered at 850¡ãC for 30 hours in this preparation. Further sintering is found to deteriorate the onset value of the sample. There was no signature of the formation of 2234 or 2245 phase in this synthesis. 1. Introduction The bismuth system superconductors are generally represented by the formula Bi2Sr2Can£¿1CunO2n+4 with critical temperature ( ) values around 10£¿K, 80£¿K, and 110£¿K for , and 3, respectively [1, 2]. Among the above, member, namely, Bi2Sr2Ca1Cu2O8 (2212), is found to be the most stable one. Preparation of member, Bi2Sr2Ca2Cu3O10 (2223), as a single phase is extremely difficult because of the intergrowth of low 2212 phase with 2223 phase. Many research groups have tried to synthesize 2223 compound as a single phase [3¨C8]. The addition of lead to the superconducting Bi-Sr-Ca-Cu-O compounds leading to the formation of 2223 phase has been reported by Wang et al. [5]. Shi et al. [6] have tried to synthesize 2223 phase by heating an off stoichiometric starting composition with excess Ca and Cu. Sastry et al. [7] have tried the matrix method to obtain a single phase 2223 compound with a £¿£¿120 K. Though there were many attempts made to synthesize (2234) and (2245) members [9, 10], no conclusive evidence is available on the structure and £¿£¿values of the above phases. In this paper we report the results of our attempt to synthesize the 2245 phase by solid state reaction method. 2. Materials and Methods The sample Bi1.65Pb0.35Sr2Ca4Cu5Oy was prepared by solid state reaction method as the combinations of two matrices M1 and M2 (M1 = Bi1.65Pb0.35Sr2Cu3Ox and M2 = 2Ca2CuO3). High purity (99.9%) Bi2O3, PbO, SrCO3, CaCO3, and CuO powders were used as starting materials. The powders with the molar ratio of [Bi]£¿:£¿[Pb]£¿:£¿[Sr]£¿:£¿[Cu] = 1.65£¿:£¿0.35£¿:£¿2£¿:£¿3 (matrix M1) and [Ca]£¿:£¿[Cu] = 4£¿:£¿2 (matrix M2) were separately prepared by thoroughly mixing the components for about an hour using an agate mortar and pestle. The final mixtures in powder form were kept in two alumina crucibles
%U http://www.hindawi.com/journals/jssp/2014/716032/