We report a study of the superconducting and normal-state properties of the filled-skutterudite system ${\mathrm{PrPt}}_4{\mathrm{Ge}}_{12-x}{\mathrm{Sb}}_x$. Polycrystalline samples with Sb concentrations up to $x=5$ were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to $x=4$, above which no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, $\gamma$, of superconducting specimens decreases with increasing $x$ up to $x=3$, suggesting that superconductivity may depend on the density of electronic states in this system. The specific heat for $x=0.5$ exhibits an exponential temperature dependence in the superconducting state, reminiscent of a nodeless superconducting energy gap. We observed evidence for a weak “rattling” mode associated with the Pr ions, characterized by an Einstein temperature ${\mathrm{\Theta }}_{\mathrm{E}}\sim 60$ K for $0\le x\le 5$; however, the rattling mode may not play any role in suppressing superconductivity.

• Received 26 October 2015
• Revised 4 January 2016

DOI:https://doi.org/10.1103/PhysRevB.93.104507