New superconducting CaSi2 phase with T-c up to 14K under pressure

Starting from trigonal and semimetallic CaSi2 we have found evidences for a new superconducting phase with onset of T-c up to 14K under pressure. In situ structural investigation shows that trigonal CaSi2 actually transforms to a new phase with hexagonal symmetry at room temperature and approximate to 90 kbar and the lattice parameters dramatically shrink at approximate to 160 kbar, The presence of sp(2) silicon arrangement seems to be the condition promoting superconductivity in this, as well as in other, silicon-based materials. (C) 2000 Elsevier Science B.V. All rights reserved.