In this work we report experimental results concerning the influence of potassium and excess copper additions on the AC complex susceptibility and microstructural development within polycrystalline YBCO high-temperature superconductors with nominal composition Y1-0.2xBa2-0.2xKxCu3Oy (x = 0-1.20). The real (X′) and the imaginary (X″) parts of the complex magnetic susceptibility of YBCO were recorded as a function of the temperature at various magnetic fields up to 10 Oe. From these data the intergranular critical current densities were calculated using Bean's critical state model. A proper concentration x, which is approximately equal to x = 0.40 in the initial Y1-0.2xBa2-0.2xKxCu3Oy batch was found to improve the Josephson coupling between the grains.
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