High-temperature resistivity of R${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{y}}$, where R=La, Pr, Nd, Sm, Eu, Dy, Ho, Er, and Tm

The electrical resistivity ρ of R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{y}}$, where R=La, Pr, Nd, Eu, Dy, Ho, Er, Sm, and Tm has been measured from room temperature up to 900 K. No essential difference in the transport properties was found except for ${\mathrm{LaBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{y}}$ and ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{y}}$ which shows an anomaly in the electrical resistivity. ${\mathrm{SmBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{y}}$ samples with various oxygen contents are studied in detail. Metallic behavior and linear temperature dependence of ρ have been found for ${\mathrm{SmBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{y}}$ with 0<y<0.227. The linear temperature dependence of ρ implies weak electron-phonon coupling, which suggests that other mechanisms for high-$T_c$ superconductivity are needed.