Study of binary and pseudo-binary intermetallic compounds with AlB2 structure

We have synthesized and studied the binary intermetallic compounds, AGa(2) and A[GaxSi2-x] (A= Sr, Ba, Ca), which are isostructural to the newly discovered 40 K superconductor MgB2. The binary compounds AGa(2) were found to be non-superconducting above 2 K, even though they have the same valence electron number per formula as MgB2 and greater lattice parameters than MgB2. However, by varying the valence electron number, they become superconducting. This result suggests that the electronic structures of this class of compounds depend on more than just the valence electron density and the lattice parameters. The theoretical prediction that the T-c of MgB2 could be enhanced with the proper dopant to increase its carrier density or to expand the lattice could not be verified. (C) 2002 Elsevier Science B.V. All rights reserved