The valence-balanced Yb 14 AlSb 11 therefore exhibits semiconductor behavior. In contrast, the Fermi energy is buried in a partially-filled valence band when M is divalent (e.g., Mg 2+ , see Figure ). Yb 14 MgSb 11 is therefore deficient of one electron per formula unit, according to charge counting: 14Yb 2+ + (MgSb 4 ) 10-+ (Sb 3 ) 7-+ 4Sb 3-+ 1h + . This indicates that the valence band is partially filled and explains why the compound exhibits behaviors of a heavily doped semiconductor. The conduction bands are largely dominated by Yb-s states, and one can therefore expect the energies of the conduction bands to be affected by the electronegativity of the A cation in