Abstract
We have observed a correlation between the lattice-constant ratio c/b and the superconducting transition temperature in R-Be-Cu-O superconductors (where R is a rare-earth element). Madelung potentials and the bond length of Cu(1)-O(3) are calculated and correlated with the distribution of over the various R superconductors. Further consideration of with variable x of suitable oxygen content leads to an explanation of the correlation of decreasing c/b ratio with increasing . A Coulomb-type ionic mechanism is therefore suggested so that shortening of the c axis and increased chain length provides (1) a channel of charge-transfer excitation from chain to Cu-O layers and (2) a long-range Coulomb interaction between the two Cu-O layers, both of which result in stronger coupling between the two Cu-O layers and higher . .AE
- Received 30 May 1989
DOI:https://doi.org/10.1103/PhysRevB.40.9408
©1989 American Physical Society