Some Evidence for Cation Disorder in YBa sub 2 Cu sub 3 O sub 7.

The high-T sub c superconductors generally have layered structures with metallic CuO sub n layers separated by semiconductive layers such as BaO. I analyze evidence that indicates that there are a few parts per hundred of Y atoms occupying Ba sites in YBa sub 2 Cu sub 3 O sub 7. These atoms are expected to provide electrical bridges between metallic CuO sub n layers.