Rare earth ionic size dependence of T-c in RBaSrCu3O7 (R = Y, Dy, Nd, and La) series

Superconducting transition temperature (T-c), measured by ac susceptibility technique, was determined for the RBaSrCu3O7 compounds with R = Y, Dy, Nd and La. Rare earth dependence of T-c in RBaSrCu3O7 series is quite differen t than that observed in RBa2Cu3O7 (R:123) Series. Neutron diffraction studi es reveal that the title compounds with R = Y, Dy crystallize in the orthor hombic R:123 structure with orthorhombicity considerably smaller than that of the R:123 compounds. In fact, the orthorhombicity reduces so much that t he RBaSrCu3O7 compounds with light rare earths, R = La and Nd, are tetragon al or almost tetragonal.