Quasicrystals are materials that fascinate scientists for more than thirty years: discovery of such materials that possess long-range translational and non-crystalographic orientational order eventually led to re-definition of the term ‘crystal’. The peculiar structure is not the only physical property that makes quasicrystals so interesting: from the point of view of transport, they closely match the concept that a good thermoelectric should have: a glasslike material in relation to phonon, and a metal in relation to electronic transport. Generally, quasicrystals are intrinsically poor thermal conductors – the lack of long-range periodicity disturbs phonon- (and consequently the heat-) flow considerably. Contrary, the charge transport is tunable by difference in compositional, impurity and sample-preparation properties, giving the opportunity to optimize their thermoelectric figure of merit. In this work we discuss charge and heat transport properties of aluminum-based quasicrystals and compare them with related materials being quasiperiodic at short- and periodic at long-range scale, known as quasicrystal approximants. The charge transport (electrical conductivity and thermoelectric power) is analyzed within the spectral conductivity model. The measured thermal conductivity data are analyzed and discussed by the model that takes into account modification of the Wiedemann-Franz law typical for the quasicrystalline structure, and contributions of both extended and localized lattice vibrations. However, the current data tend to indicate that they are not suitable candidates for a new, high-performance thermoelectrics since the considerable increase of the thermoelectric power seems not to be likely.

We present a semi-quantitative model used to analyze thermal conductivity data of single-grain aluminum-based icosahedral i-AlPdMn and i-AlFeCu, and decagonal d-AlCoNi quasicrystals in the quasiperiodic plane. The analysis is based on the validity of the WiedemannFranz law and applicability of the Debye model of quasilattice thermal conductivity at low temperatures, where the main phonon scattering centers are assumed to be structural defects in the form of the stacking faults and phenomenological quasiumklapp. At high temperature, electron and quasilattice contributions underestimate the data. This has motivated us to consider two possible additional heat-carrying channels: the activation of localized lattice vibrations and modifications of the WiedemannFranz law.

Thermal conductivity, κ, of e-phase Al 73 Pd 25 Fe 2 and Bergman phase Mg-Al-Zn is presented, which resembles the features common to all complex metallic alloys: relatively low value, shallow local maximum or change of slope at approximately 50 K, and a rise above 100 K. The electron contribution, κ el , is calculated using Wiedemann-Franz law, while the calculation of the phonon thermal conductivity, K p h , below 50 K is calculated employing Debye model. The sum of the two does not explain the experimental data at higher temperatures (above 100 K). This discrepancy is analyzed in three competitive ways: assuming an increase of an effective Lorenz number, taking into account the hopping of localized lattice vibrations, and employing a bipolar diffusion effect, known from the theory of semiconductors. While the results of the former two approaches confirm other findings in literature, bipolar diffusion effect needs to be adopted for the specific electron structure of complex metallic alloys.

The thermal conductivity (κ ) of Al73Mn27-xFex (x=0, 2, 4, 6) complex metallic alloys has been measured in the temperature interval from 2 to 300 K. All the alloys are Taylor (T) phases, except Al73Mn21Fe6, which is decagonal (d) quasicrystal. The behaviours of κ are typical for complex metallic alloys, i.e., a relatively small magnitude, a change of slope at about 50 K and an increase of the conductivity above 100 K. At room temperature the magnitude of κ for all the samples is between 2.7 and 3.3 W/mK, which is comparable to that of thermally insulating amorphous SiO2 and Zr/YO2 ceramics. The reason for such a low thermal conductivity is because both, the electronic and lattice conductivity are low. The electronic contribution to the thermal conductivity is low because of the large electrical resistivity of the samples. The lattice thermal conductivity is greatly reduced because of the enhanced umklapp process of the phonon scattering (caused by the large lattice constant) and by the disorder in the structure.

Thermal conductivity, kappa, of Taylor phase T-Al73Mn27-xPdx (x = 0, 2, 4, 6) complex metallic alloys (CMAs) has been studied in the temperature interval from 2 K to 300 K. The characteristics of kappa are typical for the CMAs: a relatively small value, a change of slope at about 50 K and an increase of slope above 100 K. The value of kappa is between 2.7 W/m K and 3.7 W/m K at room temperature. The low thermal conductivity has it's origin in a complex structure: aperiodic on a short length scale, which leads to frequent electron scattering (i.e. to a low electronic contribution to the thermal conductivity), while the large lattice constant defines a small Brillouin zone that enhances umklapp scattering of extended phonons. Above 100 K the non-extended (localized) lattice vibrations are thermally excited, and hopping gives a new heat carrying channel resulting in typical increase of the thermal conductivity with temperature.

Book Series on Complex Metallic AlloysProperties and Applications of Complex Intermetallics, pp. 113-147 (2009) No AccessTHERMAL CONDUCTIVITY OF COMPLEX METALLIC ALLOYSAna Smontara, Ante Bilušić, Željko Bihar, and Igor SmiljanićAna SmontaraLaboratory for the Study of Transport Problems, Institute of Physics, P.O. Box 304, 10000 Zagreb, Croatia, Ante BilušićLaboratory for the Study of Transport Problems, Institute of Physics, P.O. Box 304, 10000 Zagreb, Croatia, Željko BiharLaboratory for the Study of Transport Problems, Institute of Physics, P.O. Box 304, 10000 Zagreb, Croatia, and Igor SmiljanićLaboratory for the Study of Transport Problems, Institute of Physics, P.O. Box 304, 10000 Zagreb, Croatiahttps://doi.org/10.1142/9789814261647_0003Cited by:3 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The term "complex metallic compounds" comprises a great number of compounds characterized by their large unit cells that can contain up to a thousand atoms. The paper views the heat and electric transport properties of the class of these compounds known also as quasicrystalline approximants, with the unit cells formed of polytetrahedral structures also present in quasicrystals. The simultaneous long-range periodicity on the physical-length scale and the presence of nonperiodicity of polytetrahedral structures on the short-range length scale causes a crossover of space localization and delocalization of atomic vibrations and current carriers. The electrical conductivity in the temperature range 1.5 K- R.T. is weak temperature dependent that is explained as an interplay between the delocalization (due to the long-range periodicity) and the localization (due to the short range polytetrahedral order) of charge carriers, while the thermal conductivity vs. temperature behavior is similar to those for thermal insulators, with the remark that half of the net heat transport is governed by the charge carriers. FiguresReferencesRelatedDetailsCited By 3Thermal transport properties of decagonal quasicrystals and their approximantsPetar Popčević, Ante Bilušić, Kristijan Velebit and Ana Smontara25 January 2013 | MRS Proceedings, Vol. 1517Single crystal growth of Al-based intermetallic phases being approximants to quasicrystalsPeter Gille, Birgitta Bauer, Michael Hahne, Ana Smontara and Janez Dolinšek1 Mar 2011 | Journal of Crystal Growth, Vol. 318, No. 1Thermal conductivity of Taylor phase T-Al 73 Mn 27 complex metallic alloyD Stanić, P Popčević, I Smiljanić, A Bilušić and I Batistić et al.18 May 2010 | Journal of Physics: Conference Series, Vol. 226 Properties and Applications of Complex IntermetallicsMetrics History PDF download

We performed investigations of the electrical resistivity, thermopower and thermal conductivity of a monocrystalline i-Al64Cu23Fe13 as well as a polycrystalline i-Al63Cu25Fe12 icosahedral quasicrystal, for comparison. The electrical resistivity of both samples, the monocrystalline i-Al64Cu23Fe13 and the polycrystalline i-Al63Cu25Fe12, exhibits a negative temperature coefficient with rho(4K) = 3950 mu Omega cm and rho(4K)= 4900 mu Omega cm, and the ratio rho(4K)/rho(300K) = 1-8, rho(4K)/rho(300K) = 1.7, respectively. The thermopowers are large and have a negative sign. In addition, the thermopower of the monocrystalline i-Al64Cu23Fe13 exhibits a sign reversal at T = 278 K. The thermal conductivity is anomalously low, of the order of 1 W/mK at room temperature, with a slightly different temperature variation at low temperatures. On the basis of these results, we concluded that there are no systematic differences between the high-quality monocrystalline and polycrystalline icosahedral i-Al-Cu-Fe quasicrystals. Moreover, the reported transport properties of i-Al-Cu-Fe appear to be intrinsic to this family of icosahedral quasicrystals.

Istraživana su svojstva prijenosa elektricnog naboja i topline klase kompleksnih metalnih spojeva, karakteriziranih izuzetno velikim jedincnim celijama ; Mg32(Al, Zn)49 [1], ksi’ -Al74Pd22Mn4 [2], beta-Al3Mg2 i epsilon-faze (Al-Pd prijelazni metal) [3] poznatih i kao kvazikristalni aproksimanti [4], cije su j. c. izgrađene od politetraedarskih struktura prisutnih u kvazikristalima. Prisutnost periodicnosti na prostornoj skali dugoga dosega te neperiodicne politetraedarske uređenosti na skali kratkoga dosega kod tih sistema dovodi do ispreplitanja prostorne lokaliziranosti i ne-lokaliziranosti atomskih titranja i nositelja elektricnog naboja. Otpornost od 1.6 K do 300 K blago se mijenja s temperaturom, sto je, kvalitativno, objasnjeno međuigrom delokaliziranosti i lokaliziranosti nositelja naboja. Iznos je termostruje karakteristi can za metale, iako bi veliki broj atoma u jedinicnoj celiji trebao dovesti i do velikog broja raspoloživih elektronskih stanja, a toplinska je vodljivost po svome temperaturnom ponasanju slicna onoj kod izolatora.

The beta-Al3Mg2 complex metallic alloy comprises about 1168 atoms in the giant-unit cell, making this material excellent candidate to investigate how the exceptional structural complexity and the coexistence of two different length scales - one defined by the unit-cell parameters and the other by the cluster substructure - affect physical properties of a metallic material. We have investigated magnetic, electrical, thermal transport and thermoelectric properties of a monocrystalline and a polycrystalline Al3.26Mg2 sample in a mixed beta-beta ' phase, grown by the Czochralski technique. Electrical resistivity is in the range p approximate to 30-40 mu Omega cm and exhibits T-2 dependence at low temperatures and T at higher temperatures, resembling nonmagnetic amorphous alloys. Magnetic susceptibility X measurements revealed that the samples are Pauli paramagnets with significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the rho(T) and chi(T), together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy E-F was estimated by NMR and was found to amount about 90% of the DOS of the fcc Al metal. Thermal conductivity contains electronic, Debye and hopping of localized vibration terms, whereas the thermopower is small and negative. High structural complexity of the Al3Mg2 complex metallic alloy does not result in high complexity of its electronic structure. We found no evidence for the existence of a pseudogap in the DOS at E-F. (c) 2007 Elsevier Ltd. All rights reserved.

We have investigated electrical resitivity and thermal conductivity of quasicrystalline compounds of the Al-Cr-Fe system: a gamma-brass phase (-AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O1/O2-AlCrFe) with properties which are in many respects intermediate to regular metals and quasicrystals. The electrical resistivities show very weak temperature dependence and the resistivity values are in between regular metals and aluminum-based quasicrystals. Thermal conductivity data show that the electronic and lattice contributions are of comparable size. While the electronic contribution can be described by the Wiedemann–Franz law, the lattice contribution can be reproduced by a sum of a long-wavelength phonons and hopping terms. At the lowest measured temperature, scattering of phonons on stacking-fault-like defects limits the heat transport. This type of defects has also been observed in the structural investigations. The results indicate that transport properties of quasicrystalline approximants are not determined by the short-range atomic order only, but are affected by both, the short-range quasiperiodic and long-range periodic atomic orders. PACS numbers: 61.44.Br, 71.23.Ft UDC 536.21

Transport properties (electrical and thermal conductivity and thermopower) of the high-quality samples of xi'-Al-Pd-Mn and Psi-Al-Pd-Mn giant-unit-cell materials have been studied. Their electrical resistivities show weak temperature dependences between room and liquid helium temperatures, the resistivity values are higher than for regular metals and lower than for aluminum-based quasicrystals. The thermoelectric power is negative with complex temperature dependence, indicating the complexity of the electronic band structure. Thermal conductivity data show that the electronic and lattice contributions are of comparable size. While the electronic contribution can be described by the Wiedemann-Franz law, the lattice contribution could be reproduced by a sum of long-wavelength phonons and hopping of localized vibrations terms. These results that are in many respects different from both regular periodic metals and alloys and quasicrystals indicate that the transport properties of the giant-unit-cell complex metallic alloy materials are affected by both the quasiperiodic short-range atomic order and the long-range periodic order.

The Al-Pd-Mn system of intermetallics contains complex metallic alloy (CMA) phases, whose crystal structures are based on giant unit cells comprising up to more than a thousand atoms per cell. We performed investigation of the magnetic, electrical, and thermal transport and thermoelectric properties of the xi(') phase and the related Psi phase on single-crystalline samples grown by the Bridgman technique. The samples are diamagnets with a tiny paramagnetic Curie-like magnetization and an estimated fraction of magnetic Mn atoms about 100 ppm. The electrical resistivity between 300 and 4 K exhibits a temperature variation of less than 2%. The origin of this temperature-compensated resistivity is analyzed in terms of the spectral conductivity model. The thermal conductivity of the samples is small and can be described by the sum of the electronic and lattice contributions, which are of comparable size at room temperature. The lattice contribution can be reproduced by the sum of the Debye term (long-wavelength phonons) and the term due to hopping of localized vibrations. The thermoelectric power is small and negative, compatible with a low concentration of electrons as the majority charge carriers. The studied physical properties of the giant-unit-cell CMA phases in the Al-Pd-Mn system are in many respects intermediate between those of metals or simple intermetallics and quasicrystals, suggesting that both the polytetrahedral local atomic order and the large-scale periodicity influence the physical properties of the material.

Two stable approximant phases in the Al–Cr–Fe system – a gamma-brass phase (γ-AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O1/O2-AlCrFe) – were investigated using magnetic susceptibility, electrical resistivity and thermal conductivity measurements, combined with structural investigations using X-ray diffraction, light microscopy (LM) and scanning electron microscopy (SEM). The investigated approximants exhibit physical properties that are in many respects between those of regular metals and quasicrystals (QCs); their electrical resistivities show very weak temperature dependences and the resistivity values are higher than for regular metals and lower than for Al-based QCs. The magnetic susceptibility results show the existence of a small fraction (of about 1% for the γ-AlCrFe and about 10 times less for the O1/O2-AlCrFe) of localized magnetic moments with Curie-like temperature dependence. Thermal conductivity measurements show that the electronic and lattice contributions are of comparable size at room temperature. While the electronic contribution can be described by the Wiedemann–Franz law, the lattice contribution can be reproduced by the sum of the Debye term (long-wavelength phonons) and the term due to hopping of localized vibrations. At the lowest measured temperature (8K), scattering of phonons on stacking-fault-like defects limits the heat transport, and this type of defect has also been observed in the LM and SEM structural investigations.

The thermal conductivity of the charge-density-wave compound K0.3MoO3 has been investigated in the chain direction and in both perpendicular directions. A strong anisotropy is observed in the temperature range 100–300 K. The detailed analysis of the temperature dependence in all three directions confirms that in addition to the lattice and free carriers there are very anisotropic contributions to the thermal conductivity coming from the phase and amplitude fluctuations.

The thermal conductivity of the charge-density-wave compound K0.3MoO3 has been investigated in the chain direction and in both perpendicular directions. A strong anisotropy is observed in the temperature range 100–300 K. The detailed analysis of the temperature dependence in all three directions confirms that in addition to the lattice and free carriers there are very anisotropic contributions to the thermal conductivity coming from the phase and amplitude fluctuations.

We have measured the thermal conductivity of K 0.3 MoO 3 (blue bronze) in the chain direction and in both perpendicular directions from 80 to 300 K. As expected, it shows an anisotropic behaviour in lattice contribution as well as in free carrier contribution. These results are in favor to our previous explanation that there are residual anomalies in thermal conductivity resulting from the contribution of low-frequency phasons of rather large velocities.

We report about the measurements of the thermal conductivity, K, of the quasi-one dimensional conductors (TaSe4)2I and (NbSe4)3I in the temperature region between 70 mK and 4K, and we compare them to the data which we obtained with the second experimental method between 1.2K and 10K. The behaviour of K for (NbSe4)3I is almost regular compared to the other dielectric materials, namely it goes like T2.7 in the low temperature regime close to expected boundary scattering regime, while in the case of (TaSe4)2I, it exhibits a pronounced anomaly which has the shape of broad minimum around 3K. The anomaly can be related to an excess specific heat in the same temperature range. We ascribe this anomaly to a strong photon scattering by phonons of low-lying transverse acoustic modes only propagative in a restricted part of the Brillouin zone.