Superconductivity, magnetism and structural study of some new ternary transition metal borides

Superconductivy has been found in the rare iridium borides with the general formulae MIr4B4 and in the pseudoternary (Y/sub x/Lu/sub 1-x/)Ir4B4systems, where M can be Ho, Er or Tm. The compounds were found to crystallize with the primitive tetragonal CeCo4B4-type structure and the pure phase in itself is only metastable at best. The close correlation between superconductivity, magnetism and structural metastability is demonstrated with the study of the pseudoternary systems M(Ir/sub x/Rh/sub 1-x/)4B4(x = 0.25, 0.5 and 0.9) in general, and through the Er(Ir/sub x/Rh/sub 1-x/)4B4, Ho(Ir/sub x/Rh/sub 1-x/)4B4 systems, in particular. The boundaries between the paramagnetic, superconducting and magnetically ordered phases in the Ho(Ir/sub x/Rh/sub/1-x/)4B4 system have been established. The boundaries between the paramagnetic, superconducting and magnetically ordered phases in the Dy(Ir/sub x/Rh/sub 1-x/)4B4 also have been established. The occurrence of superconductivity with an onset of 7.2 K is reported for the metastable ScRu4B4 compound, a new member of the body-centered-tetragonal LuRu4B4-type structure MRu4B4 systems. Superconducting and crystallographic data for the pseudoternary system (Sc/sub x/Lu/sub 1-x/)Ru4B4 are also presented and discussed. Three new ternary transition metal boride classes with the CeCo3B2-type, ErIr3B2-type and YOs3B4-type structures are reported with the general formulae: MT3B2, where T is one of the transition metals Ru, Os, Ru or Ir, and M can be Sc, Y, Th, U or one of the rare earth (RE) elements. Finally, two ternary boride systems with the new LuRuB2-type structure are reported. Superconductivity as high as 10.0 K is found for the LuRuB2 compound