Effect of sulfur on the superconductivity of RBa2Cu3O7

The single-phase high-Tc superconductor RBa2Cu3O6S R=Nd, Eu, Gd, Y, Er have been prepared and studied by x-ray diffraction and dc magnetometry. For Gd and Y the compounds with sulfur have a larger unit cell and yet have the same Tc. For R=Eu, Nd substitution of 1 oxygen by sulfur suppresses Tc and causes the crystal structure to change from orthorhombic to tetragonal. TbBa2Cu3O7-xSx, x=0,1 systems crystallize in a perovskite-related cubic structure and are neither superconducting nor magnetically ordered down to 2 K. The sulfur oxidizes the Tb so that it is tetravalent.