Structural properties of Ba2RCu3O7 high-Tc superconductors

Abstract
The crystal chemistry of several Ba2RCu3O7 high-Tc superconductors (R=Y,Pr,Sm,Eu,Gd,Dy,Ho,Er,Tm) has been studied by x-ray diffraction on twinned crystals. All samples except the Pr compound show superconductivity around 90 K. From the variation of the interatomic distances with different rare-earth ions, we infer the presence of a [CuO2-BaO-CuO□-BaO-CuO2] building unit.