STRUCTURAL DISTORTION AND SUPERCONDUCTIVITY IN (ND1-XTBX)(1.85)CE0.15CUO4

The phase diagram of (Nd1-xTbx)(1.85)Ce0.15CuO4 has been studied by re sistivity, magnetic susceptibility, x-ray, electron-, and neutron-diff raction experiments. For low-Tb concentrations the samples are superco nducting; however, T-c diminishes rapidly with increasing x. For highe r Tb concentrations all diffraction studies indicate the long-range la ttice deformation characterized by the rotation of the CuO, squares ar ound the c axis (i.e., the orthorhombic phase recently observed in Gd2 CuO4); the structural consequences of the distortion are discussed.