The variation of superconducting transition temperature (${\mathit{T}}_{\mathit{c}}$) with hydrostatic pressure up to 21 kbar is reported for compounds in the pseudoternary systems (${\mathrm{Lu}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sc}}_{\mathit{x}}$${)}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$ (0.05≤x≤0.95) and (${\mathrm{Lu}}_{0.9}$${\mathit{R}}_{0.1}$${)}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$ (R=Dy, Ho, Er, Tm, Sc, Y, and Th). Measurements of the temperature dependence of the electrical resistivity and ac magnetic susceptibility for (${\mathrm{Lu}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sc}}_{\mathit{x}}$${)}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$ (0.005≤x≤0.02) are made to show the correlation between the decrease of the charge-density-wave formation temperature (${\mathit{T}}_0$) and the increase of ${\mathit{T}}_{\mathit{c}}$. (${\mathrm{Lu}}_{0.98}$${\mathrm{Sc}}_{0.02}$${)}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$ and ${\mathrm{Lu}}_5$(${\mathrm{Ir}}_{0.78}$${\mathrm{Rh}}_{0.22}$${)}_4$${\mathrm{Si}}_{10}$, which have ${\mathit{T}}_{\mathit{c}}$ about 2 K higher than ${\mathrm{Lu}}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$, are used to study the enhanced superconducting state with upper-critical-magnetic-field measurements. Changes in the electronic density of states at the Fermi level and the electron-phonon interaction play an important role in these pseudoternary compounds.

• Received 2 July 1990

DOI:https://doi.org/10.1103/PhysRevB.43.7681