Superconductivity in the C32 intermetallic compounds AAl2-xSix,with A = Ca and Sr, and 0.6<x<1.2

The intermetallic compounds AAl(2-x)Si(x), where A = Ca, Sr or Ba, crystallize in the C32 structure, same as the recently discovered MgB2 with a high superconducting transition temperature of 39 K. For x = 1, superconductivity has been observed in AAlSi with A = Ca and Sr, but not with A = Ba. The transition temperatures are 7.8 and 5.1 K, respectively for CaAlSi and SrAlSi. The CaAl2-xSix compound system display a T-c-peak at x = 1, a possible x-induced electronic transition at x similar to 0.75 and a possible miscibility gap near x similar to 1.1 which results in a very broad superconducting transition. The Seebeck coefficients of AAlSi indicate that their carriers are predominantly electrons in nature, in contrast to the holes in MgB2. (C) 2002 Elsevier Science B.V. All rights reserved.