Superconductivity in a New Pseudo-Binary Li₂B(Pd_1-<i>x</i>Pt_<i>x</i>)₃ (<i>x</i>=0–1) Boride System

Abstract

Recently we have found superconductivity in a cubic antiperovskite-like compound Li 2 BPd 3 . A new pseudo-binary complete solid solution Li 2 B(Pd 1- x Pt x ) 3 , x =0–1 with similar structure has been synthesized and observation of superconductivity in the entire x -range is reported. Our results strongly suggest that superconductivity is of bulk type. Critical temperature T c is decreasing approximately linearly with amount ( x ) of Pt from 7.2–8 K for Li 2 BPd 3 to 2.2–2.8 K for Li 2 BPt 3 . From isothermal magnetization ( M – H ) measurements, lower critical fields H c1 (138 Oe/ x =0 , 38 Oe/ x =1 ), upper critical fields H c2 WHH (3.4 T/ x =0 , 1 T/ x =1 ), coherence length ξ(0) (9.8 nm/ x =0 , 17.9 nm/ x =1 ) and penetration depth λ(0) (190 nm/ x =0 , 364 nm x =1 ) were estimated and shown to follow approximately linear dependencies with x , either. Structure and superconducting similarities with MgCNi 3 , viewed as a bridge between low and high T c superconductors are increasing the expectations that Li 2 B(Pd 1- x Pt x ) 3 , x =0–1 superconductor can be included in the same class of `intermediate' superconductors. For x =0–1 a weak fish-tail effect was observed at low and intermediate fields. Apart from this effect, some samples for x =1 have shown magnetization jumps at fields close to H c2 .