Structure and superconductivity studies on ternary equiatomic silicides, MM'Si

Abstract

A series of ternary equiatiomic transition metal silicides MM'Si (M=Zr, Nb, Ta;M'=Ru, Re) and Zr_½M_½RuSi (M=Nb, Ta) have been synthesized and characterized. Guinier X-ray data clearly indicate that the compounds MM'Si (M=Nb, Ta;M'=Ru, Re) crystallize with the orthorhombic TiFeSi-structure. This is contrary to one of the literature reports ascribing the hexagonal ZrRuSi structure to MReSi, M=Nb, Ta. ZrRuSi and Zr_½M_½RuSi (M=Nb, Ta), however, crystallize with the ZrRuSi structure. All the compounds are metallic and exhibit small and negative Seebeck coefficients. Superconductivity has been discovered in MM'Si, M=Nb, Ta; M'=Ru, Re and the transition temperatures, as measured by the low frequency a.c. susceptibility technique, range from 2.7 to 5.1 K. Zr_½Nb_½RuSi is not superconducting above 2.2 K. The observed properties are explained in terms of the electronic charge transfer effects and crystal structures adopted by these metal excess ternary silicides.