SUPERCONDUCTING AND CALORIMETRIC PROPERTIES OF THPT2B2C AND THE ANOMALOUS T-C VARIATION FOR NONMAGNETIC RPT(2)B(2)C SYSTEMS (R=Y,TH,LA)

Superconducting quantum interference device dc magnetic susceptibility , ac magnetic susceptibility, ac electrical resistivity, and specific- heat measurements on bulk and powder samples of ThPt2B2C shows a bulk superconducting transition T-c of 7 K with a transition width of 6.6-7 .4 K. The low-temperature normal-state specific-heat data yield an ele ctronic-term coefficient gamma of 8.5 mJ/mol K-2, a Debye temperature theta(D) of 330 K, and a bulk superconducting specific-heat jump Delta C at a T-c of 1.53 gamma T-c. Contrary to the smooth variation of T-c with the T-T in-plane distance for the nonmagnetic RT(2)B(2)C systems (R = Y,Th, La; T = Ni, Pd), an anomalous T-c variation with the Pt-Pt in-plane distance d(Pt-Pt) was observed for the nonmagnetic RPt(2)B(2 )C system (R = Y, Th, La). This anomalous T,-d(Pt-Pt) relationship, al ong with the specific-heat gamma value and normal-state Pauli paramagn etic susceptibility of lower-T-c ThPt2B2C, suggests the importance of the Pt(Sd)-dominated conduction band.