The variation of the superconducting transition temperature ($T_c$) with hydrostatic pressure up to 23.7 kbar is reported for eleven ternary silicides and germanides with the ${\mathrm{Sc}}_5$${\mathrm{Co}}_4$${\mathrm{Si}}_{10}$-type structure. Most of these compounds display a modest linear depression of $T_c$ with pressure (${\mathrm{dT}}_c$/dp∼${10}^{\mathrm{-}5}$ K/bar); however, two materials, ${\mathrm{Lu}}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$ and ${\mathrm{Lu}}_5$${\mathrm{Rh}}_4$${\mathrm{Si}}_{10}$, undergo a discontinuous transformation to a state with a significantly higher $T_c$ above a critical pressure of about 20 kbar. For ${\mathrm{Lu}}_5$${\mathrm{Ir}}_4$${\mathrm{Si}}_{10}$, the pressure-enhanced $T_c$ of 9.12 K is the highest transition temperature reported for this class of compounds.

• Received 26 December 1985

DOI:https://doi.org/10.1103/PhysRevB.33.5062