AC susceptibility study of Bi1.66Pb0.34Sr2Ca2-xMgxCu3Oy (x = 0, 0.2 and 0.4) superconductor systems

A systematic study of the intergranular properties of Bi1.66Pb0.34Sr2Ca2-xMgxCu3Oy (x = 0, 0.2 and 0.4) samples has been done, using the AC susceptibility technique. The samples were prepared by conventional solid state reaction method. It was found that Mg substitution in place of Ca reduces the intergranular coupling of Bi-2223 system. Analysis of the temperature dependence of the AC susceptibility near the transition temperature (Tc) has been done employing Bean's Critical State Model. The observed variation of intergranular critical current densities (Jc) with temperature indicates that the critical current density decreases by increasing the amount of Mg. The higher electronegativity of Mg in the unit cell promotes more intake of oxygen in the material, and the grain boundaries are in more over-doped regime. These over-doped regions reduce the intergranular coupling and increases weak link behavior of Mg doped samples