Superconductivity at 27 K in T sup 1 - Nd sub 2 CuO sub (4- x) F sub x.

Single-phase fluorinated cuprates M sub 2 CuO sub (4-x) F sub x (M=Pr, Nd) can be prepared up to a limiting composition x approximately equals 0.3-0.4). The fluorinated phases have the T sup 1-Nd sub 2 CuO sub 4 structure, are n-type conductors at room temperature, and exhibit bulk superconductivity with onset temperatures as high as 27 K. These compounds are the first high T sub c superconductors to be prepared by anionic substitution in cuprates.