The upper critical fields $B_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ were measured up to 28 T for $R_1{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$, where $R=\mathrm{N}\mathrm{d},\mathrm{E}\mathrm{u},\mathrm{G}\mathrm{d},\mathrm{D}\mathrm{y},\mathrm{H}\mathrm{o},\mathrm{E}\mathrm{r},\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{T}\mathrm{m}$, and for $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$. The midpoints ${\left(\frac{d{B}_{c2\mathrm{}}}{\mathrm{dT}}\right)}_{T=T_c}$ cluster about (2.8±0.2) T/K, the $T_c\text{'}\mathrm{s}=(93\mathrm{}\pm 2)$ K show a slight systematic decrease from Nd to Tm, and the extrapolated values of $B_{c2\mathrm{}}\mathrm{}\left(0\right)\mathrm{}$ cluster about (160±20) T. The wide range of normal-state resistivities indicates that they are not intrinsic to the superconductor. The anisotropy $A=\frac{B_{c2\mathrm{}\parallel }}{B_{c2\mathrm{}}\perp }$ is estimated to be less than 12 based on the data for the resistive transition. Criteria for the midpoint resistive transition are also reexamined.

• Received 26 May 1987

DOI:https://doi.org/10.1103/PhysRevB.36.2394