MECHANISM OF THE TC ENHANCEMENT IN BI2SR2CACU2O8+Y BY SODIUM DOPING

Superconductivity in Na-doped Bi2Sr2CaCu2O8+y has been investigated and a T(c) of 94 K and T(o) of 90 K have been achieved through the use of a melting process. A careful X-ray diffraction study on the Na-doped samples revealed that, with increasing Na content, the a and c axes increased, the b axis decreased, and the unit cell volume increased, indicating that Na was introduced into the lattice. This was further confirmed by EDS and chemical analyses. Substitution of Na for divalent atoms will reduce the oxygen content due to the requirement of charge balance, giving rise to an effect similar to that from quenching or during heat treatment under low oxygen partial pressures, either of which is necessary to achieve a T(c) of 90 K in undoped samples.