Anomalously largeTcdepression by Zn substitution in Y-Ba-Cu-O

A systematic study of $T_c$ variation on Zn substitution for Cu in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ is reported. $T_c$ decreases linearly from 89 K to the nonsuperconducting state at an unusually large rate of over 15 K/at.% of substitution. Over the entire concentration range no orthorhombic-to-tetragonal change is observed. The $T_c$ depression and the negative $\frac{\mathrm{dR}}{\mathrm{dT}}$ found for higher Zn concentration have been attributed to some of the unique characteristics of Zn.