Intrinsic electrical, magnetic, and thermal properties of single-crystallineAl64Cu23Fe13icosahedral quasicrystal: Experiment and modeling

Abstract

In order to test for the true intrinsic properties of icosahedral i-Al-Cu-Fe quasicrystals, we performed investigations of magnetism, electrical resistivity, thermoelectric power, and thermal conductivity on a singlecrystalline Al 64 Cu 23 Fe 13 quasicrystal grown by the Czochralski technique. This sample shows superior quasicrystallinity, an almost phason-free structure, and excellent thermal stability. Magnetic measurements revealed that the sample is best classified as a weak paramagnet. Electrical resistivity exhibits a negative temperature coefficient with 4 K = 3950 ⍀ cm and R = 4 K / 300 K = 1.8, whereas the thermopower exhibits a sign reversal at T = 278 K. Simultaneous analysis of the resistivity and thermopower using spectral-conductivity model showed that the Fermi energy is located at the minimum of the pseudogap in the spectral conductivity ͑͒. Thermal conductivity is anomalously low for an alloy of metallic elements. Comparing the physical properties of the investigated single-crystalline Al 64 Cu 23 Fe 13 quasicrystal to literature reports on polycrystalline i-Al-Cu-Fe material, we conclude that there are no systematic differences between the high-quality singlecrystalline and polycrystalline i-Al-Cu-Fe quasicrystals, except for the hindering of long-range transport by grain boundaries in the polycrystalline material. The so far reported physical properties of i-Al-Cu-Fe appear to be intrinsic to this family of icosahedral quasicrystals, regardless of the form of the material.

Thermal conductivity of the Al-based quasicrystals and approximants

“…One may, therefore, wonder that it could be a possible origin for the unusual increase of thermal conductivity observed for our present samples. The analysis in the context of VRH-P may reproduce the thermal conductivity of our present samples partly because it uses a parameter fitting with which the increasing tendency is somehow accounted for and partly because the data is limited in a narrow temperature range below 400 K. However the fitting solely with VRH-P is rather poor both for the present materials and those in the literature [15,16], and the scenario solely with VRH-P cannot account for the characteristic composition dependence of j 00 ðTÞ experimentally obtained in our study. Therefore we conclude that VRH-P is not the dominant mechanism leading to the unusual behavior in thermal conductivity of the present samples.…”

“…Before closing discussion, we also comment on the variable range hopping conduction of phonons (VRH-P) predicted by Janot [9]. This mechanism is sometimes employed to account for the unusual increase of thermal conductivity at high temperature for the icosahedral quasicrystals [8,15,16]. One may, therefore, wonder that it could be a possible origin for the unusual increase of thermal conductivity observed for our present samples.…”

Thermal conductivity in complex metallic alloys: Beyond Wiedemann-Franz law

“…The absence of such a well-defined pseudogap in the case of Ј and ⌿-AlPdMn samples indicates that the electrical conductivity is consequently higher. Thus, the origin of the almost temperature-independent electrical conductivity reported for both the Ј and ⌿-AlPdMn alloys 24 can be then traced back to the specific form of the spectral conductivity, which exhibits very weak variation over the energy scale of several meV around the Fermi level. Yet, they show some fine struc- ture that yields observable effects in the temperaturedependent thermoelectric power curves.…”

Anisotropic electrical and thermal conductivities of the Al76Co22Ni2 decagonal approximant

“…This is because in these regions the electrons are scattered elastically. Therefore, at T $ 10-100 K deviations from the law are observed which imply that l e /s(T) Á T depends on T [9]. In this way estimated lattice thermal conductivity l lat gives an indication of the anisotropy of the phonon spectrum.…”

“…The temperature dependent Lorentz number L(T) in the limit T ! 0, goes towards the empirical Wiedemann-Franz law value L o ¼ 2.45 Â 10 À8 WK À2 [9]. Note, the empirical Wiedemann-Franz law l e ¼ L o Á s(T) Á T is valid at very low temperatures (T 10 K) and at high (room) temperatures.…”