Investigation of various substitution effects on BiPbSrCaCuO type high temperature ceramic superconductors

ABSTRACT In this work, elemental substitutional effects on the structural and superconducting properties of Bii.7Pbo.3Sr2Ca2-xM(Zn,Ag)xCu30y system were investigated. Our aim was an investigation the effects of substitution of elements with different ionic radii respect to replaced element. Partial molar replacement of Ca by ZnO and A^O was investigated in x=0.00 - 0.20 substitutional range. Samples prepared with conventional solid state reaction method were sintered at 850°C after pressed under 375 MPa pressure. Critical temperatures of samples were determined by resistivity-temperature measurements made in liquid nitrogen conditions. XRD measurements were done by powder x-ray diffraction method. Data on the granular structure of samples were obtained from scanning electron microscope (SEM) photographs with X2000 magnification. Additional data about properties of the system was observed by density measurements made by Archimedes water displacement method and by calculations of volume fraction of high-Tc phase obtained from XRD results. Tc values for ZnO substituted samples are in 95-110 K range while for Ag20 substituted samples are in 106-1 15 K range. All samples in both substitutional group, show narrow transition width which gives information about purity of samples. X-ray diffraction datum indicates that samples have multiphase structure and contain 2223 phase as main phase. Volume fraction results, calculated withVI intensities of L(008) and H(0010) peaks, in both group increase with substitutional ratio, but have higher value for Ag20 group. The density values for all.samples are almost same and are less than the theoretical density. Smaller density is sign of the less compact form and pores between grains. Comparison of SEM microphotographs indicates that in both group plate-like grain alignment is dominant. But for Ag20 substitution samples higher grain size provides stronger contact, which improves superconducting properties. Substituted elements have different ionic radii than Ca, ionic radii of ZnO is smaller while Ag20's is higher. This difference of ionic radii may be responsible for variation of the structure of system. Results show that Ag2Û plays better role in improvement of the superconducting properties than the ZnO.