Anomalous effects of Cu-doping on structural and thermoelectric properties of the Al-Ir cubic quasicrystalline approximant

Iwasaki, Yutaka; Kitahara, Koichi; Kimura, Kaoru

doi:10.1016/j.jallcom.2018.05.199

Cited by 8 publications

(10 citation statements)

References 30 publications

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“…Quasicrystals and their approximants that are composed of aluminium and transition-metal elements have been intensively studied as thermoelectric materials over the last two decades 115) because they often show electrical properties (electrical conductivity • and Seebeck coefficient S) comparable to those of degenerate semiconductors and thermal conductivity ¬ comparable to that of glass. Although most of the quasicrystals and approximants investigated so far showed a relatively small «S« (approximately 120 µV/K 8) or smaller 111, 13,14) ), a semiconducting approximant recently discovered by Iwasaki et al 15) showed a large «S« of approximately 200 µV/K, which is comparable to that of practical thermoelectric materials. Following that breakthrough, the development of high-performance thermoelectric materials in quasicrystals and approximants may be expected.…”

Section: Introductionmentioning

confidence: 88%

Interband Contribution to Thermoelectric Properties of Al–Cu–Ir Quasicrystalline Approximant

Kitahara

Kimura

2021

Mater. Trans.

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Section: Introductionmentioning

confidence: 88%

Interband Contribution to Thermoelectric Properties of Al–Cu–Ir Quasicrystalline Approximant

Kitahara

Kimura

2021

Mater. Trans.

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“…In this case, while the C phase has a primitive cubic lattice, the C 1 and C 2 phases are 2 × 2 × 2 superlattice structures of the C phase and have body-centered-and face-centered-cubic lattices, respectively. While a semiconducting band structure was predicted for the Al-Ir C phase, our previous experimental results for the TE properties showed metallic behavior because of the vacancies of the inner cluster Al sites [19]. These vacancies have a serious effect on the band structure, leading to a downward shift of the Fermi energy to the valence band and loss of the band gap.In this Rapid Communication, we have performed an orbital analysis of the Al-Ir C phase using DFT calculations to obtain a guideline to enable control of the band gap.…”

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confidence: 70%

Experimental realization of a semiconducting quasicrystalline approximant in Al-Si-Ru system by band engineering

Iwasaki

Kitahara

Kimura

2019

Phys. Rev. Materials

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We found that an Al-Si-Ru cubic quasicrystalline approximant has a semiconducting band structure by performing an orbital analysis based on density functional theory. These semiconducting transport properties have been confirmed in an experimentally synthesized sample. The temperature dependences of the electrical conductivity and the Seebeck coefficient were consistent with the trends of an intrinsic semiconductor with a band gap of 0.15 eV above 350 K. The lattice thermal conductivity had a low value of approximately 1.0 W m −1 K −1 above 400 K, which is close to the theoretical minimum.Since the discovery of the quasicrystal (QC) in 1984 [1], many of the unique properties of QCs have been revealed, including their crystal structures [2] and electrical properties [3]. However, the question of whether or not semiconducting or insulating QCs exist remains one of the fundamental problems to be solved in solid state physics, although the QC concept has been established as one of the categories of solid-state structures.Semiconducting QCs have attracted attention, not only from the perspective of academic interest, but also from the viewpoint of application to thermoelectric (TE) materials to realize a direct conversion between the thermal and electrical energies. The performance of a TE material can be evaluated using the dimensionless figure of merit zT = S 2 σ T /(κ el + κ lat ), where S, σ , T , κ el , and κ lat are the Seebeck coefficient, the electrical conductivity, the absolute temperature, the electronic thermal conductivity, and the lattice thermal conductivity, respectively. The highest zT between QCs achieved to date is 0.26, which is only approximately one quarter of the general target value of unity, at 500 K in an Al-Ga-Pd-Mn QC [4]. The main problem is that the value of S (≈100 μV K −1 ) is only approximately one half of that of typical practical materials. To obtain a sufficiently large S at a target temperature T , a semiconductor with a band gap of 6-10k B T , where k B is the Boltzmann constant, is generally required [5]. Therefore, the discovery of a semiconducting QC is necessary to enable the breakthrough of QCs for use as TE materials.While semiconductorlike properties that were attributed to a combination of the pseudogap in the density of states (DOS) and electronic weak localization were previously reported in some aluminum-transition metal (Al-TM) QCs [6-10] and quasicrystalline approximants (QCAs) [10,11], a finite band gap has yet to be observed experimentally in these materials to date. There have been several theoretical works on semiconducting QCAs based on density functional theory (DFT) that have thus far contributed to the understanding of the problem of complex semiconducting QCs. Krajčí and Hafner investigated the electronic structures of hypothetical QCAs that were constructed using a model of Al-TM icosahedral QCs [12][13][14]. While they predicted the existence of some QCAs with semiconducting electronic structures and indicated the presence of an energy gap in QCs, these typ...

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“…13) However, when such a sample was prepared and assessed experimentally, its thermoelectric properties showed metallic behavior rather than semiconducting behavior, so its thermoelectric performance was poor. 10) Experimental and calculated results have suggested that the metallic behavior in this material originates from excess carriers (holes) caused by Al vacancies inside the cluster. Thus, suppressing these Al vacancies is key to producing a semiconducting AlIr quasicrystalline approximant.…”

Section: Introductionmentioning

confidence: 94%

“…To do so, raw powders of Al (4N, Kojundo Chemical Laboratory Co., Ltd.) and Ir (3N, Tanaka Kikinzoku Kogyo Co., Ltd.) were compacted into pellets with a composition of Al 73.3 Ir 26.7 and melted in an arc-melting furnace. These ingots were homogenized by annealing at 1273 K for 72 h. We sintered them at a uniaxial pressure of 80 MPa for 20 min, because in our previous research 10) on the same material, applying a uniaxial pressure of 50 MPa generated an insufficient relative density (95(2)%).…”

Section: Experimental and Calculation Proceduresmentioning

confidence: 99%

“…The refinement of the lattice constant a and the composition of the sample were analyzed in the same way as in our previous studies. 7,10) The true density of the sample was measured by helium displacement method using a dry pycnometer (AccuPyc1330, Micrometrics). The thermal conductivity ¬ of the sample was measured using the laser flash method (TC-7000, Advance Riko Co., Ltd.).…”

Section: Experimental and Calculation Proceduresmentioning

confidence: 99%

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Vacancy Control and Enhancement of Thermoelectric Properties of Al–Ir Cubic Quasicrystalline Approximant via High-Pressure Synthesis

2020

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Although the binary AlIr cubic quasicrystalline approximant has been expected to be a narrow-gap semiconductor, it has not yet been produced because the presence of Al site vacancies causes excess hole doping. We suggest that high-pressure synthesis (HPS) can effectively reduce these vacancies. In this work, we investigated how HPS affected the structural and thermoelectric properties of an AlIr quasicrystalline approximant, finding that the sample made by HPS had a larger Seebeck coefficient than a sample made by conventional spark plasma sintering (SPS). Further, applying high pressure increased the lattice constant and measured Al composition by increasing the number of Al atoms in the Ir 12 icosahedral cluster. These results show that HPS suppressed vacancies in the cluster, which doubled the dimensionless figure of merit zT.

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Anomalous effects of Cu-doping on structural and thermoelectric properties of the Al-Ir cubic quasicrystalline approximant

Cited by 8 publications

References 30 publications

Interband Contribution to Thermoelectric Properties of Al–Cu–Ir Quasicrystalline Approximant

Interband Contribution to Thermoelectric Properties of Al–Cu–Ir Quasicrystalline Approximant

Experimental realization of a semiconducting quasicrystalline approximant in Al-Si-Ru system by band engineering

Vacancy Control and Enhancement of Thermoelectric Properties of Al–Ir Cubic Quasicrystalline Approximant via High-Pressure Synthesis

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