Study of substitution effects on structure and properties of high temperature superconductors and isostructure compunds

Abstract

The thesis mainly describes the investigation of the structural formation of higher order members of bismuth system of superconductors Bi1.6sPb0.35Sr2CazCu4Oy (n = 4, 2234 phase), Bi1.6sPb0.35Sr2Ca4CusOy (n = 5, 2245 phase) and Bi1.65Pb0.35Sr2CasCu,Oy (n = 9, 2289 phase). The samples were synthesized by solid state reaction technique. Micro-structural and morphological features of the synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS). The XRD pattern of all the samples revealed the presence of Bismuth 2212 and 2223 phases of which 2223 phase was found to be the predominant. Superconducting transition temperature (Tc) of the samples measured by self-inductance method and dc four probe method showed Tc value around 110 K. There was no signature of the formation of 2234, 2245 or 2289 phases in this investigation. newlineFormation of Bi-2245 compound was further investigated by preparing the sample in a new matrix route. The Tc on set of this sample was found to be 127 K which was the highest reported ever in bismuth system superconductors. The complete replacement of copper by nickel in bismuth system superconductor Bi2SraCu06 (2201) was ttempted by preparing the sample in air by solid state reaction method under open and closed environment. Morphological and microstructural features of the synthesized sample Bi2Sr2Ni0g was investigated by X-ray diffraction, SEM and EDAX. The analysis of X-ray diffraction pattern revealed that nickel can replace copper completely and form a single phase Bi2Sr2Ni06 only when prepared in a closed environment in air. This phase formation of BizSr2NiOo was reported first time. newline