Ph.D. Tezi Görüntüleme

       In this study, the effect of ZnO addition on the microstructure, mechanic and magnetic properties of the YBCO have been investigated through XRD, SEM, EDX, AC susceptibility measurements and the standart Vickers microhardness method. The samples were prepared by two different methods namely, conventional solid state reaction method ( Samples S1, S2 and S3 ) and melt process ( S4, S5 and S6 ) in order to compare the dopant effect on the YBCO system (0, 0.5 and 1wt% of ZnO respectively) in both methods.

       With increasing content of ZnO addition to YBCO, the hardness was increased while transition temperature was decreased. The hardness was found to be load dependent in the low load range. For sample S4, Vickers hardness was increased with decreasing temperature up to (1824 MPa). The hardness at 40K was around 3.5 times higher than the hardness at room temperature (517 MPa). On the other hand, for sample S6, Vickers hardness was increased with decreasing temperature up to (2316 MPa). The hardness at 40K was about 2 times higher than the hardness at room temperature (1075 MPa). Thermal activation energies of samples S4 and S6 were found to be (345.8 J/mol) and (255.5 J/mol) respectively. At load-displacement experiments carried out for samples S4 and S6 at low temperatures, no creep was observed when the load was kept fixed for 15 seconds.

       Keywords: YBCO Superconductor, ZnO addition, Hardness, Thermal activation energy, Critical current density, AC susceptibility