Low-temperature heat-capacity study of superconducting ternary silicides and germanides with the Sc5Co4Si10-type structure

Abstract

The results of low-temperature specific-heat experiments on eleven superconducting compounds belonging to the ternary system $R_5$ $T_4$ $X_{10}$ (R=Sc, Y, and Lu; T=Co, Rh, Ir, and Os; X=Si and Ge) are presented. Analysis of the data yields relatively high Debye temperatures for the silicides (300–600 K), as well as large values for ΔC/γ$T_c$ (2.8–4.9) and the electron-phonon interaction λ (0.60–0.75) for the high-$T_c$ compounds ${\mathrm{Sc}}_5$ ${\mathrm{Rh}}_4$ ${\mathrm{Si}}_{10}$, ${\mathrm{Sc}}_5$ ${\mathrm{Ir}}_4$ ${\mathrm{Si}}_{10}$, and ${\mathrm{Y}}_5$ ${\mathrm{Os}}_4$ ${\mathrm{Ge}}_{10}$, indicating that these are strong-coupled superconductors. The analysis also indicates that a large contribution of the anharmonic term to the total specific heat in the normal state is present in the low-$T_c$ compounds. It is apparent that the phonon spectra of these ${\mathrm{Sc}}_5$ ${\mathrm{Co}}_4$ ${\mathrm{Si}}_{10}$-type materials are quite complex.