REACTION BETWEEN DIFFERENT STRUCTURAL BLOCKS AND ITS INFLUENCE ON SUPERCONDUCTIVITY IN TL₂BA₂CA_N-1CU_NO_2N+3

The non-monotonic relationship of T_c with the number of Cu-O planes (n) per unit cell for compounds of Tl₂Ba₂Ca_n-1Cu_nO_2n+3 (n=1, 2, 3, 4 and 5) is investigated from the reaction between different structural blocks. The unit cell of the Tl superconductors is treated as two blocks: the perovskite block where the Cu-O planes are located and the rock salt block, which is considered as a charge-reservoir. A model was used to calculate the combinative energy of the two blocks. It is found that the combinative energy between the two blocks is closely related to the value of T_c. The relation demonstrates an interesting way to understand the nonlinear change of T_c with the number of Cu-O planes in the layered superconductors. This means that the interaction between the two blocks plays an important role in superconductivity. The results are somewhat different from that of another Tl-system superconductor, Tl₂Ba₂Ca_n-1Cu_nO_2n+4, with 4 superconductive compounds.