Superconductivity in a new pseudo-binary Li2B(Pd1-xPtx)3 (x=0-1) boride system

Recently we have found superconductivity in a cubic antiperovskite-like compound Li2BPd3. A new pseudo-binary complete solid solution Li2B(Pd1-xPtx)(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, is decreasing approximately linearly with amount (x) of Pt from 7.2-8 K for Li2BPd3 to 2.2-2.8 K for Li2BPt3. From isothermal magnetization (M-H) measurements, lower critical fields H-cl (138Oe/(x=0), 38Oe/(x=1)), upper critical fields H-c2(WHH) (3.4 T/(x=0), 1 T/(x=1)), coherence length xi(0) (9.8 nm/(x=0), 17.9 nm/(x=1)) and penetration depth lambda(0) (190nm/(x=0), 364nm(x=1)) were estimated and shown to follow approximately linear dependencies with.x, either. Structure and superconducting similarities with MgCNi3, viewed as a bridge between low and high T-C superconductors are increasing the expectations that Li2B(Pd1-xPtx)(3), x = 0-1 superconductor can be included in the same class of `intermediate' superconductors. For x = 0-1 a weak fishtail 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.