We find the oxygen isotope shift in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ is 0.18±0.04 K with ∼85% ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ substitution, in disagreement with a recent published result. The methods used to measure a small shift in $T_c$ of a ceramic oxide superconductor are discussed: sample preparation, reversible isotope substitution, measurement at low field, and control of temperature drift. We find α=0.019±0.005 in the relation $T_c$∝$M^{\mathrm{-}\alpha }$. .AE

• Received 11 December 1987

DOI:https://doi.org/10.1103/PhysRevB.37.5936