We employ the chemical fragment formalism to perform a targeted superconductor search in the Nb-Ru-B system, yielding the orthorhombic metal-rich boride NbRuB, which displays BCS-like superconductivity with a Tc = 3.1 K. NbRuB is derived from the che
mical fragments Nb3B2 + Ru3B, in which the Nb3B2 fragment contains B-B dimers and the Ru3B fragment contains isolated B atoms. A charge transfer occurs between the fragments. The results indicate that the fragment formalism is a useful chemical tool for the design of new intermetallic superconductors much the same way as the charge reservoir concept has been a useful chemical tool for the design of new copper oxide superconductors.
Based on the interplay of theory and experiment, a large new family of filled group 9 (Co, Rh and Ir) skutterudites is designed and synthesized. The new materials fill the empty cages in the structures of the known binary CoSb3, RhSb3 and IrSb3 skutt
erudites with alkaline, alkaline earth, and rare earth atoms to create compounds of the type AyB4X12; A atoms fill the cages to a fraction y, B are the group 9 transition metals, and X is a mixture of electronegative main group elements chosen to achieve chemical stability by adjusting the electron counts to electron-precise values. Forty-three new compounds are reported, antimony-tin and phosphorous-silicon based, with 63 compositional variations presented. The new family of compounds is large and general. The results described here can be extended to the synthesis of hundreds of new group 9 filled skutterudites.
