Bizmut tabanlı süperiletkenlerde tanecik sinirlari ve Ag-seramik arayüzün özellikleri

The main objective of this thesis was the preparation of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox/Ag multilayered samples (2, 4 and 8 layers) and to investigation of the effect of multilayering with Ag on the superconducting and the microstructural properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox. Towards that end, we have done a three main investigations: 1) Studied the optimal annealing temperature for bettering superconducting properties, 2) Investigated the effect of diffusion doped Ag on the microstructure and superconducting properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox and 3) Studied the effect of Ag layering on the superconducting and microstructural properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox.First, we prepared Bi1.8Pb0.4Ca2.2Sr2Cu3Ox ceramic superconductors annealed at 830, 835, 840, 845, and 850 °C using the solid state reaction method to investigate the optimum annealing temperature. The investigations consist of XRD, SEM, dc resistivity and transport critical current density measurements. The highest Tc and Jc values were found to be 106 K and 124 A/cm2 for the sample annealed at 840 °C for 48 hours (B840), respectively. Large grain size, denser surface and high volume fraction of the high-Tc phase were obtained for the sample B840.Then, we prepared silver diffusion doped Bi1.8Pb0.4Ca2.2Sr2Cu3Ox to investigate the effect of the silver diffusion on the microstructural and superconducting properties and to calculate silver diffusion coefficient and activation energy in Bi1.8Pb0.4Ca2.2Sr2Cu3Ox. The diffusion doping of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox by silver increased the critical current density from 123 to 696 A/cm2 and the transition critical temperature by about 3 K compared with the undoped sample. Ag-doping increased the amount of high-Tc phase and improved the surface morphology. It also causes an increase of the lattice parameter c by an amount of 0.15%. The temperature dependence of the silver diffusion coefficient in the range of 600-800°C is described by D = 2.9x10-4 exp(- 1.05 eV/kBT).Finally, Bi1.8Pb0.4Ca2.2Sr2Cu3Ox/Ag multilayered samples (2, 4 and 8 layers) were fabricated by powder in tube (PIT) method. PIT technique consists of filling the powder into the silver tube, drawing, rolling, pressing and annealing procedure. The rolling process was not effective in obtaining further substantially increases of the powder density, but greatly improved the orientation of ceramic grains inside the silver sheath. XRD, SEM, dc electrical resistivity as a function of temperature and magnetic field, critical current density at 77 K as a function of magnetic field measurements were performed to investigate the effect of Ag layering on microstructural and superconducting properties of multilayered samples. The sample is composed of a highly oriented Bi-2223 phase in the region near the Ag layer. The eight-layered sample exhibits a rather high Ic value of 126 A. Tc and Jc are enhanced from 107 K to 109 K and from 240 A/cm2 to 600 A/cm2 by increasing the number of Ag layers, respectively. The reason for improving Jc properties is that grain growth near the Ag region was progressed with extending layers. The formation of the dense oriented structure is near the interface between oxide and the Ag layer. This suggests that Ag plays an important role in the improvement of Jc. The enhancement of Jc is achieved by an increase in interface are between Ag and Bi-oxide.