A neutron diffraction study of the superconductor, $Tl_{0.5}Pb_{0.5}CaSr_2Cu_2O_y$

The structure of $Tl_{0.5}Pb_{0.5}CaSr_2Cu_2O_y$ $(T_c = 90K)$ has been investigated by neutron diffraction profile analysis and the results discussed in the light of the structures of $TlCaBa_2CuP_2C_y$ and $TlCa_{0.5}Y_{0.5}Ba_2Cu_2O_y$. We find no evidence for disorder in the Tl/Pb sites, but there is some interchange between Ca and Sr sites. The Cu---O bond distances in these cuprates seem to parallel the variation of the superconducting transition temperature in these cuprates