Superconducting quantum interference device dc magnetic susceptibility, ac magnetic susceptibility, ac electrical resistivity, and specific-heat measurements on bulk and powder samples of ${\mathrm{ThPt}}_2$${\mathrm{B}}_2$C shows a bulk superconducting transition ${\mathit{T}}_{\mathit{c}}$ of 7 K with a transition width of 6.6–7.4 K. The low-temperature normal-state specific-heat data yield an electronic-term coefficient γ of 8.5 mJ/mol ${\mathrm{K}}^2$, a Debye temperature ${\mathrm{\theta }}_{\mathit{D}}$ of 330 K, and a bulk superconducting specific-heat jump ΔC at a ${\mathit{T}}_{\mathit{c}}$ of 1.53 γ${\mathit{T}}_{\mathit{c}}$. Contrary to the smooth variation of ${\mathit{T}}_{\mathit{c}}$ with the T-T in-plane distance for the nonmagnetic ${\mathit{RT}}_2$${\mathrm{B}}_2$C systems (R = Y, Th, La; T = Ni, Pd), an anomalous ${\mathit{T}}_{\mathit{c}}$ variation with the Pt-Pt in-plane distance d(Pt-Pt) was observed for the nonmagnetic R${\mathrm{Pt}}_2$${\mathrm{B}}_2$C system (R = Y, Th, La). This anomalous ${\mathit{T}}_{\mathit{c}}$-d(Pt-Pt) relationship, along with the specific-heat γ value and normal-state Pauli paramagnetic susceptibility of lower-${\mathit{T}}_{\mathit{c}}$ ${\mathrm{ThPt}}_2$${\mathrm{B}}_2$C, suggests the importance of the Pt(5d)-dominated conduction band. © 1996 The American Physical Society.

• Received 21 September 1995

DOI:https://doi.org/10.1103/PhysRevB.53.3492