engleski

Origin of anisotropic nonmetallic transport in Al80Cr15Fe5 decagonal approximant

We present a study of the anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient and lattice thermal conductivity) of a single-crystalline Al80Cr15Fe5 complex metallic alloy that is an excellent approximant to the decagonal quasicrystal with six atomic layers in one periodicity unit. Temperature-dependent electrical resistivity along the b and c crystalline directions shows nonmetallic behavior with a broad maximum, whereas it shows metallic positive temperature coefficient along the a direction perpendicular to the (b, c) atomic planes. Ab-initio calculations of the electronic density of states reveal that the nonmetallic transport occurs in the presence of a high density of charge carriers. The very different T-dependent electrical resistivities along the three crystalline directions can all be treated within the same physical model of slow charge carriers due to weak dispersion of the electronic bands, where the increased electron-phonon scattering upon raising the temperature induces transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulatinglike) regime. The T-dependence of the resistivity is governed predominantly by the T-dependence of the electronic diffusion constant D and the transition has no resemblance to the Anderson-type metal-to-insulator transition based on gradual electron localization. Structural considerations of the Al80Cr15Fe5 phase show that the anisotropy of the transport properties is a consequence of anisotropic complex local atomic order on the scale of nearest-neighbor atoms, suggesting that the role of quasiperiodicity in the anisotropic transport of decagonal quasicrystals is marginal.

61.44.Br; 71.23.Ft

This work was supported in a part by the 6th Framework EU Network of Excellence 'Complex Metallic Alloys' (Contract No. NMP3-CT-2005-500140).