90 K SUPERCONDUCTING PHASE IN THE R-Tl-Sr-Cu-O SYSTEMS WITH R=RARE EARTHS

Abstract

We have observed superconductivity at 90 K in the R-Tl-Sr-Cu-O systems with R=rare earths by resistance and ac susceptibility measurements. The 90 K phase (for R=Pr) can be assigned as a tetragonal Tl(Sr, Pr) 3 Cu 2 O x with a unit cell of a=3.8629 ±0.0006 Å and c=12.1671±0.0018 Å. The formation of the 90 K phase depends on rare earths, nominal compositions, and preparation conditions.