New double-sheet copper oxide compounds with BiO or TIO bilayers

ONE of the main families of oxide superconductors comprises compounds with varying numbers of CuO2 sheets sandwiched between BiO or TIO bilayers1-5. The superconducting transition temperature (Tc) in these compounds increases with the number of CuO2 sheets; for example, Tc is 80-108 K for the double-sheet 2212 phase, and 110-125 K for the triple-sheet 2223 phase. Here we describe a new family of double-sheet copper oxide compounds with BiO or TIO bilayers, which can improve our understanding of the relationship between Tc and the CuO2 sheets. The new compounds, Bi2Sr2(Ln1-xCex)2Cu 2O10+y, and Tl2Ba2(Ln1-xCex)2Cu 2O10+y (where Ln is Sm, Eu or Gd), have double CuO2 pyramidal sheets between double BiO or TIO layered units, like the 2212 phase, but with a different arrangement of adjacent CuO2 sheets. The new bismuth compounds (Bi-2222) have a significantly lower Tc (∼30 K or less) than the 2212 or 2223 phases, even when the charge-carrier (hole) concentrations are comparable. So far, we have not found superconductivity in the Tl-2222 compounds. © 1989 Nature Publishing Group.