Origin of the DOS pseudogap and Hume-Rothery stabilization mechanism in RT-type Al _(48)Mg _(64)Zn _(48) and Al _(84)Li _(52)Cu _(24) 1/1-1/1-1/1 approximants

摘要

Full-potential linearized plane wave (FLAPW) band calculations with subsequent FLAPW-Fourier analyses have been performed for two RTtype Al _(48)Mg _(64)Zn _(48) and Al _(84)Li _(52)Cu _(24) 1/1-1/1-1/1 approximants containing 160 atoms per unit cell. The FLAPW-Fourier analysis revealed that the Fermi surface-Brillouin zone (FsBz) interactions involving more than two sets of lattice planes are responsible for the formation of a pseudogap across the Fermi level in both compounds. The most critical sets of lattice planes interfering with electrons at the Fermi level are deduced to be {543}+{710}+{550} with |G| ~2 = 50 in the former and {631} with |G| ~2 = 46 in the latter. The square of the Fermi diameter (2kF) ~2 is determined to be 49.9±0.1 and 47.1±0.4 in units of (2π/a) ~2, respectively, where a is the lattice constant. Hence, the matching condition (2kF) ~2 = |G| ~2 holds well in both compounds. It is also shown that, while a shallow pseudogap in the Al _(48)Mg _(64)Zn _(48) approximant can be ascribed solely to the FsBz interactions, a much deeper one in the Al _(84)Li _(52)Cu _(24) approximant is explained as a superposition of the FsBz interactions and the formation of strongly directional bonding states between Cu-4p and Al-3p orbitals.