Mg-doping into boron icosahedral duster solids, targeting high temperature superconductivity

Abstract

  High-T_c superconductivity may be possible upon metallic-element doping into boron icosahedral cluster solids. We attempted magnesium (Mg) doping into α-rhombohedral boron (α-B₁₂) and β-rhombohedral boron (β-B₁₀₅), and discussed the possibility of metal transition and superconductivity. Although the preparation of Mg-doped α-B₁₂ cannot be achieved, we achieved Mg doping into β-B₁₀₅ at a high Mg concentration of up to MgB_11.5 (8.6 Mg/cell), which. is the highest metal concentration of β-B₁₀₅ up to now. However, neither metal transition nor superconductivity was observed. We estimated the density of states (DOS) near E_F and discussed the electronic states of β-B₁₀₅. From the result, it is suggested that a localized state exists above the intrinsic acceptor level probably originating from the B₂₈ cluster with structural defects.