Classification of Icosahedral Quasicrystals and their Approximants by the Electronic Conduction Mechanisms
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Classification of icosahedral quasicrystals and their approximants by the electronic conduction mechanisms Tsunehiro Takeuchi1, Eiichi Banno1, Tomohide Onogi1, Takayuki Mizuno1, Takuya Sato1, Fournée Vincent1, 2, and Uichiro Mizutani1 1 2
Department of Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603 Japan Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
ABSTRACT In this paper, two independent factors, electronic structure at the Fermi energy and electron scattering, both of which determine the electrical resistivity, are clearly separated by using a plot of ρ4K versus RRR (RRR = ρ4K/ρ300K) for icosahedral quasicrystals and their approximants. Each contribution of the electronic structure and the electron scattering on the electrical resistivity was systematically revealed, and the origin for the high resistivities observed in the quasicrystals and approximants is well understood by taking each effect into account. We found that the quasicrystals and approximants are classified into three groups in terms of the electron scattering mechanism, which dominates the temperature dependence of the resistivity. The temperature dependence of the electrical resistivity in the first group is well understood in terms of the Boltzmann transport mechanism, and those in the second and the third groups are in terms of the weak localization and the Anderson localization, respectively.
INTRODUCTION One of the most attractive issues today in the field of quasicrystals (QCs) and approximants (ACs) is to investigate the origin of their extremely high resistivities observed in some QCs and ACs. Those high resistivities have been successfully interpreted in terms of the weak localization (WL), the square-root T dependence of conductivity caused by the electron-electron interaction (EEI) [1], the variable range hopping conduction [2], the generalized Ziman formula [3], and the Mott’s g2-dependence (g =N(EF)/N(EF)free) [2]. Since all of these theories are originally developed for disordered materials, the QC and AC can be classified into a class of the disordered materials. Therefore, the mean free path of the conduction electron in the QCs and ACs is expected to be shorter than a few tens of angstroms, so that the long range structure order may no longer affect electrical resistivities except for its contribution to the formation of the pseudogap. This is confirmed by paying attention to the fact that some of the quasicrystals of extremely high structural quality, such as Zn-Mg-Ho [4] and Al-Mg-Zn [5], possess resistivities of only 150 - 250 µΩcm. Therefore, it is of great importance to find out factors, other than the quasiperiodicity, which make the electrical resistivity in some QCs and ACs extremely large. Here we consider that two factors independently determine the metallic conductivity; one is the electronic structure at EF and the other is the electron scattering. Although both factors simultaneously and independently contribute to an increase in the electrical resistivity of
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