Dopant effects on the superconductivity of YBa sub 2 Cu sub 3 O sub 7 ceramics.

We investigated the effects of SrTiO sub 3 and seventeen different oxide dopants, namely Ca, Sc, La and Zr with possible substitution in the yttrium sites, K, Sr and Pb in the barium sites and Li, Mg, Fe, Co, Ni, Zn, Al, Ti, Nb and Si in the copper sites on the superconductivity of YBa sub 2 Cu sub 3 O sub 7. These dopants can be classified into four categories depending on their solubilities and substitution in the different cation sublattices of YBa sub 2 Cu sub 3 O sub 7 perovskite. Dopants in the first category dissolve and substitute in the copper sublattice and they can significantly reduce the transition temperature of the superconductivity of YBa sub 2 Cu sub 3 O sub 7. For example, three dopants in this category, namely Zn, Mg and Li, at 2 mole % dopant level, reduce the transition temperatures to 66, 65 and 82K respectively.