We report resistivity results in argon-processed Y-Ba-Cu-O, similar to those recently reported in Eu-${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathrm{\delta }}$, which were interpreted as possible indication of $T_c$ above 200 K. Scanning Auger microanalysis indicated measurable argon at the surface. However the observed results cannot be accounted for as solely due to surface effects, but may be due to an incipient metal-to-insulator transition around 220 K, and of an insulator ‘‘phase’’ formed on the grain boundaries and on the surface due to argon treatment.

• Received 20 August 1987

DOI:https://doi.org/10.1103/PhysRevB.37.1594