The a-b anisotropy of the normal-state resistivity ${\mathrm{\rho }}_{\mathit{a}}$/${\mathrm{\rho }}_{\mathit{b}}$ of untwinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ has been studied on six crystals using the Montgomery method. ${\mathrm{\rho }}_{\mathit{a}}$/${\mathrm{\rho }}_{\mathit{b}}$ increases with increasing temperature and reaches a (sample-dependent) value of 1.2–1.85 near room temperature. The wide variation of this value is attributed to the high sensitivity of the chain resistance to oxygen disorder. The temperature dependence of ${\mathrm{\rho }}_{\mathit{a}}$/${\mathrm{\rho }}_{\mathit{b}}$ can be modeled by a parallel circuit of metallic chains and superconducting planes with excess conductivity due to superconducting fluctuations in the planes at temperatures below 150 K.

• Received 27 July 1990

DOI:https://doi.org/10.1103/PhysRevB.42.10189