Structural and superconducting properties of La2-xRxBa2CayCu4+yO10+delta (R=Nd, Gd; y=2x) system

A nonsuperconducting La2Ba2Cu4O9 + delta system has been made superconducti ng by the addition of CaCuO2, along with rare earth doping at the La site, with the stoichiometric composition La2 - xRxCayBa2Cu4 + yO10 + delta (R = Nd, Gd, and y = 2x). All the samples with 0.0 < x < 0.5; y = 2x were charac terized by x-ray diffraction and neutron diffraction measurements for struc tural properties and by ac susceptibility, dc resistivity, and iodometric a nalysis for superconducting properties. The x = 0.0 sample displays semicon ducting behavior. Increasing x increases T-c from less than 15 K for Nd/Gd samples with x = 0.1 to similar to 78 K for x = 0.5 samples. It is interest ing to note that the hole concentration and T-c exhibit a strong correlatio n with increasing dopant concentration. Neutron diffraction studies confirm the occupancy of Ca and Nd ions at the La site with a concomitant displace ment of La on to the Ba site. (C) 2001 American Institute of Physics.