SUBSTITUTION OF MERCURY FOR THALLIUM IN THE 2223-CUPRATE - THE 130K-SUPERCONDUCTOR TL1.6HG0.4BA2CA2CU3O10-DELTA

A new superconductor, Tl1.6Hg0.4Ba2Ca2Cu3O10+delta , has been synthesi zed, with a Tc of 130K and a diamagnetic volume fraction of 38%. The p ossibility to substitute mercury for thallium in the 2223 cuprate is d emonstrated. The refined cell parameters, a = 3.843 (1) angstrom and c = 35.816 angstrom (7) are close to those of the undoped oxide. The el ectron diffraction and high resolution electron microscopy investigati ons evidence that the stacking of the layers along cBAR is more perfec t than in the pure 2223 thallium cuprate. Some regular intergrowths of the 2223 and the 2212 members are observed. Critical temperature and diamagnetic volume fraction are slightly improved by annealing under r educing atmosphere. The role of mercury is discussed.