We report measurements of upper critical fields ${\mathit{H}}_{\mathit{c}2}$ of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals, with x varying from 0 to 0.54. Values of ${\mathit{H}}_{\mathit{c}2}$ were determined resistively. For various Pr concentrations, we find that ${\mathit{H}}_{\mathit{c}2}$ shows a linear temperature dependence under a field up to 5 T both parallel and perpendicular to the c axis. The coherence length ${\xi }_{\mathit{a}\mathit{b}}$(0), ${\xi }_{\mathit{c}}$(0), and zero-temperature upper critical field ${\mathit{H}}_{\mathit{c}2}$(0) for various Pr concentrations and field configurations are derived from these experimental results. A possible mechanism responsible for the observed composition dependence of the normalized upper-critical-field slope in the H∥c case is discussed.

• Received 15 October 1991

DOI:https://doi.org/10.1103/PhysRevB.45.10609