Neutron structural studies of the superconducting (Nd1-yCay)Ba2(Cu0.94Ga0.06)3Oz system

We investigate the influence of Ca ions on the structural and superconducting properties of (Nd1-yCay)Ba-2(Cu0.94Ga0.06)(3)O-z system by Rietveld refinement of the neutron diffraction patterns of three samples with y = 0.0 (A(1)), y = 0.18 (A(2)), and y = 0.36 (A(3)) along with X-ray diffraction, resistivity, and ac susceptibility measurements. Samples A(2) and A(3) are superconducting with T-c values of 37 K and 76 K, respectively, whereas sample A(1) is semiconducting to 20 K. Neutron diffraction data confirms (a) the occurrence of a single-phase tetragonal structure (space group Pmmm) for all three samples; (b) Ca ions substitute at the Nd site; and (c) increasing y from 0.0 to 0.36 decreases Cu(1)-O(1), Cu(2)-O(2), and NdCu(2) bond lengths, whereas Cu(2)-O(4) bond length increases with corresponding increase in T-c to 76 K due to increasing occupancy of Ca ions at Nd site. A correlation exists between the Cu(1)-O(1), Cu(2)-O(2), Cu(2)-O(4), and Nd-Cu(2) bond lengths and the measured T-c values of three samples.