CHEMICAL BONDING TOPOLOGY OF SUPERCONDUCTORS .4. HEAVY-FERMION SUPERCONDUCTORS

Heavy fermion superconductors can be classified into the following two types based on their structures: (1) ternary transition metal carbide s, borides, and silicides containing f-block metals exhibiting stable multiple oxidation states such as cerium in CeCu2Si2, CeRu3B2, and CeR u3Si2 or uranium in URu2Si2 and U2PtC2; (2) binary alloys containing m ultiple oxidation state actinides (particularly uranium) and nonactini de polyhedral clusters such as Be-13 centered icosahedra in UBe13 and Pt-6/2 octahedra in UPt3. The f-block metals in heavy fermion supercon ductors not only exhibit multiple oxidation states but are also dilute d enough by the other elements so that the separation between f-block metals in the structure is at least 4 Angstrom. The f-block metals bec ome part of the conducting skeletons of heavy fermion superconductors so that their conductivities arise at least partially through valence fluctuations involving f-electrons. (C) 1997 Academic Press.