NEUTRON-DIFFRACTION STUDY OF SUPERCONDUCTING RESR(2)CU(3-X)M(X)O(Z) (M=RE,W)

Superconductivity has recently been reported in RESr(2)CU(2.85)Re(0.15 )O(x) (RE = Y,Tb,Dy,Ho,Er and Tm) and RESr(2)Cu(2.80)W(0.20)O(x) (RE = Y, Dy, Ho and Er) with T-c ranging from 22 to 41 K. Room temperature powder neutron diffraction studies have been carried out for obtaining structural parameters and their relation with superconductivity in th ese materials. Reitveld refinements were carried out adopting the spac e groups P4/mmm (tetragonal). Occupancy of the rare earths is less tha n 1 indicating vacancy at the rare earth sites. Cu(2)-O distance in RE Sr(2)Cu(3-x)M(x)O(z) (M = Re and W) is smaller than that of REBa(2)Cu( 3)O(7-delta) which is consistent with the smaller ionic radius of Sr2. Our studies show that the M-cations (Re or W) occupy the Cu(1) chain site.