Electronic structure of superconducting MgB2 and related binary and ternary borides - art. no. 020502

First-principles full potential linear muffin-tin orbital-generalized gradi ent approximation electronic structure calculations of the new medium-T-C s uperconductor (MTSC) MgB2 and related diborides indicate that superconducti vity in these compounds is related to the existence of p(x,y)-band holes at the Gamma point. Based on these calculations, we explain the absence of me dium-T-C superconductivity for BeB2, AlB2, ScB2, and YB2. The simulation of a number of MgB2-based ternary systems using a supercell approach demonstr ates that (i) the electron doping of MgB2 (i.e., MgB2-yXy. with X = Be, C, N, O) and the creation of defects in the boron sublattice (nonstoichiometri c MgB2-y) are not favorable for superconductivity, and (ii) a possible way of searching for similar or higher MTSC should be via hole doping of MgB2 ( CaB2) or isoelectronic substitution of Mg (i.e., Mg1-xMxB2 with M = Be, Ca, Li, Na, Cu, Zn) or creating layered superstructures of the MgB2/CaB2 type.