AC SUSCEPTIBILITY AND MICROSTRUCTURE OF ALKALI DOPED POLYCRYSTALLINE YBCO HTSC MATERIALS

In this work we report experimental results concerning the influence o f potassium and excess copper additions on the AC complex susceptibili ty and microstructural development within polycrystalline YBCO high-te mperature superconductors with nominal composition Y1-0.2xBa2-0.2xKxCu 3Oy (x = 0-1.20). The real (chi') and the imaginary (chi '') parts of the complex magnetic susceptibility of YBCO were recorded as a functio n of the temperature at various magnetic fields up to 10 Oe. From thes e data the intergranular critical current densities were calculated us ing Bean's critical state model. A proper concentration x, which is ap proximately equal to x = 0.40 in the initial Y1-0.2xBa2-0.2xKxCu3Oy ba tch was found to improve the Josephson coupling between the grains.