MATERIALS EXHIBITING SUPERCONDUCTIVITY ABOVE 90 degree KELVIN.

The authors have found superconductivity in the 90 K-range in ABa//2Cu//3O//6 with A equals La, Nd, Sm, Eu, Gd, Ho, Er and Lu in addition to Y. The results suggest that the unique square planar Cu-atoms, each surrounded by 4 or 6 oxygen atoms are considered to be crucial to the superconductivity observed in oxides in general. In particular, the superconductivity in the 90 K-range in ABa//2Cu//3O//6// plus //x is attributed mainly to the quasi-two-dimensional assembly of the CuO//2-Ba-CuO//2// plus //x-Ba-CuO//2 layers sandwiched between the A-layers, with particular emphasis in the CuO//2// plus //x layers. The results are discussed in terms of existing theories including the bipolaron and the one-dimensional theories.