X-ray powder-diffraction, magnetic-susceptibility $\chi \mathrm{}\left(T\right),$ and electrical resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ measurements were made on single crystals of the filled skutterudite series $\mathrm{Pr}({\mathrm{Os}}_{1-x}{\mathrm{Ru}}_x{)}_4{\mathrm{Sb}}_{12}.$ One end of the series $\mathrm{}(x=0\mathrm{})\mathrm{}$ is a heavy fermion superconductor with a superconducting critical temperature $T_c=1.85\mathrm{}\mathrm{K},$ while the other end $\mathrm{}(x=1\mathrm{})\mathrm{}$ is a conventional superconductor with $T_c\approx 1\mathrm{K}.$ The lattice constant a decreases approximately linearly with increasing Ru concentration x. As Ru (Os) is substituted for Os (Ru), $T_c$ decreases nearly linearly with substituent concentration and exhibits a minimum with a value of $T_c=0.75\mathrm{}\mathrm{K}$ at $x=0.6,$ suggesting that the two types of superconductivity compete with one another. Crystalline electric field effects in ${\chi }_{\mathrm{dc}}\mathrm{}\left(T\right)\mathrm{}$ and $\rho \mathrm{}\left(T\right)\mathrm{}$ due to the splitting of the ${\mathrm{Pr}}^{3+}$ ninefold degenerate Hund’s rule $J=4\mathrm{}$ multiplet are observed throughout the series, with the splitting between the ground state and the first excited state increasing monotonically as x increases. The fits to the ${\chi }_{\mathrm{dc}}\mathrm{}\left(T\right)\mathrm{}$ and $\rho \mathrm{}\left(T\right)\mathrm{}$ data are consistent with a ${\Gamma }_3$ doublet ground state for all values of x, although reasonable fits can be obtained for a ${\Gamma }_1$ ground state for x values near the end member compounds $(x=0\mathrm{}$ or $x=1).\mathrm{}$

• Received 1 July 2003

DOI:https://doi.org/10.1103/PhysRevB.69.024523