ORALS

SESSION: SISAMMonAM-R2	Mizutani International Symposium (6th Intl. Symp. on Science of Intelligent & Sustainable Advanced Materials (SISAM))
Mon. 28 Nov. 2022 / Room: Ballroom A
Session Chairs: Jean-Marie Dubois; Session Monitor: TBA

11:55: [SISAMMonAM02] OS Plenary
The theoretical Hume-Rothery electron concentration rule in designing new functional materials with a pseudogap across the Fermi level (Part 1)
Uichiro Mizutani¹ ; Hirokazu Sato² ; ¹Nagoya Industrial Science Research Institute, Nagoya, Japan; ²Aichi University of Education, Kariya-shi, Japan;
Paper Id: 373 [Abstract]

The lecture will address one of the key aspects of the behavior of electrons in metallic systems, which explains why certain specific atomic architectures form in so-called intermetallics. This mechanism is known after the name of its discoverer, William Hume-Rothery (1899-1968), a most famous British metallurgist. The Hume-Rothery electron concentration rule was empirically established by Hume-Rothery (1926) almost a century ago [1] and has significantly affected subsequent tremendous developments in the field of metal physics. Academic aspirations have been revived in the late 1980s to early 1990s, when stable quasicrystals were synthesized by using the empirical Hume-Rothery rule as a guide [2]. We have soon realized that a pseudogap at the Fermi level plays a key role in stabilizing these complex compounds. Mizutani and Sato developed a unique electron theory of metals, which allows us to link the Hume-Rothery rule with the formation of a pseudogap [3-5]. It fully relies on the interference phenomena of itinerant electrons with the set of lattice planes, regardless of the degree of orbital hybridization effects involved, and the theoretical Hume-Rothery rule thus established have been extended to alloys and compounds with bonding types of metallic, ionic, or covalent, or a changing mixture of these, unless the number of itinerant electrons in the valence band is too low. The original Hume-Rothery rule was claimed to hold in randomly substituted alloys. More recently, we have confirmed that the theoretical Hume-Rothery rule is extendable to randomly substituted alloys beyond first-principles electronic structure calculations. It has therefore direct relevance to a huge variety of compounds that show electronic conductivity. Examples are quasicrystals Al₈₆Mn₁₄ [6], Al₆₅Cu₂₀Fe₁₅ [2], Samson compound Al₃Mg₂ containing 1178 atoms per unit cell [7], amorphous alloys V_xSi_100-x (x>20) [8], marginal conductor FeS₂ [9] and so on.

References:
[1] W. Hume-Rothery, J. Inst. Metals, 35 (1926) 295.
[2] An-Pang Tsai, A. Inoue and T. Masumoto, Jpn. J. Appl. Phys. 26 (1987) L1505-L1507.
[3] U. Mizutani, “<i>Hume-Rothery Rules for Structurally Complex Alloy Phases</i>”, CRC Press, Taylor & Francis Group, Boca Raton, Florida, (2010).
[4] U. Mizutani and H. Sato, Crystals, 7 (2017) 1-112.
[5] U. Mizutani, H. Sato and T. B. Massalski, Prog. Mat. Sci. 120 (2021) 100719-1-36.
[6] D. Shechtman, I. Blech, D. Gratias and J. W. Cahn, Phys. Rev. Letters 53 (1984) 1951-1953.
[7] S. Samson, Acta Crystallogr. 19 (1965) 401-413.
[8] U. Mizutani, T. Ishizuka and T. Fukunaga, J.Phys.: Condens.Matter 9 (1997) 5333-5353.
[9] T. Homma, U. Mizutani and H. Sato, Philos. Mag., 100 (2020) 426-455.

SESSION: SISAMMonAM-R2	Mizutani International Symposium (6th Intl. Symp. on Science of Intelligent & Sustainable Advanced Materials (SISAM))
Mon. 28 Nov. 2022 / Room: Ballroom A
Session Chairs: Jean-Marie Dubois; Session Monitor: TBA

12:20: [SISAMMonAM03] OS Plenary
The theoretical Hume-Rothery electron concentration rule in designing new functional materials with a pseudogap across the Fermi level (Part 2)
Uichiro Mizutani¹ ; Hirokazu Sato² ; ¹Nagoya Industrial Science Research Institute, Nagoya, Japan; ²Aichi University of Education, Kariya-shi, Japan;
Paper Id: 451 [Abstract]

The lecture will address one of the key aspects of the behavior of electrons in metallic systems, which explains why certain specific atomic architectures form in so-called intermetallics. This mechanism is known after the name of its discoverer, William Hume-Rothery (1899-1968), a most famous British metallurgist. The Hume-Rothery electron concentration rule was empirically established by Hume-Rothery (1926) almost a century ago [1] and has significantly affected subsequent tremendous developments in the field of metal physics. Academic aspirations have been revived in the late 1980s to early 1990s, when stable quasicrystals were synthesized by using the empirical Hume-Rothery rule as a guide [2]. We have soon realized that a pseudogap at the Fermi level plays a key role in stabilizing these complex compounds. Mizutani and Sato developed a unique electron theory of metals, which allows us to link the Hume-Rothery rule with the formation of a pseudogap [3-5]. It fully relies on the interference phenomena of itinerant electrons with the set of lattice planes, regardless of the degree of orbital hybridization effects involved, and the theoretical Hume-Rothery rule thus established have been extended to alloys and compounds with bonding types of metallic, ionic, or covalent, or a changing mixture of these, unless the number of itinerant electrons in the valence band is too low. The original Hume-Rothery rule was claimed to hold in randomly substituted alloys. More recently, we have confirmed that the theoretical Hume-Rothery rule is extendable to randomly substituted alloys beyond first-principles electronic structure calculations. It has therefore direct relevance to a huge variety of compounds that show electronic conductivity. Examples are quasicrystals Al86Mn14 [6], Al65Cu20Fe15 [2], Samson compound Al3Mg2 containing 1178 atoms per unit cell [7], amorphous alloys VxSi100-x (x>20) [8], marginal conductor FeS2 [9] and so on.

References:
[1] W. Hume-Rothery, J. Inst. Metals, 35 (1926) 295.
[2] An-Pang Tsai, A. Inoue and T. Masumoto, Jpn. J. Appl. Phys. 26 (1987) L1505-L1507.
[3] U. Mizutani, “Hume-Rothery Rules for Structurally Complex Alloy Phases”, CRC Press, Taylor & Francis Group, Boca Raton, Florida, (2010).
[4] U. Mizutani and H. Sato, Crystals, 7 (2017) 1-112.
[5] U. Mizutani, H. Sato and T. B. Massalski, Prog. Mat. Sci. 120 (2021) 100719-1-36.
[6] D. Shechtman, I. Blech, D. Gratias and J. W. Cahn, Phys. Rev. Letters 53 (1984) 1951-1953.
[7] S. Samson, Acta Crystallogr. 19 (1965) 401-413.
[8] U. Mizutani, T. Ishizuka and T. Fukunaga, J.Phys.: Condens.Matter 9 (1997) 5333-5353.
[9] T. Homma, U. Mizutani and H. Sato, Philos. Mag., 100 (2020) 426-455.

SESSION: SISAMMonPM2-R2	Mizutani International Symposium (6th Intl. Symp. on Science of Intelligent & Sustainable Advanced Materials (SISAM))
Mon. 28 Nov. 2022 / Room: Ballroom A
Session Chairs: Tomoyuki Homma; Session Monitor: TBA

16:20: [SISAMMonPM210] OL Invited
INTERPRETATION of TEMPERATURE DEPENDENCE of THERMOELECTRIC PROPERTIES in FeS&lt;sub&gt;2&lt;/sub&gt; by FIRST PRINCIPLE CALCULATIONS
Tomoyuki Homma¹ ; Uichiro Mizutani² ; Hirokazu Sato³ ; Manabu Inukai⁴ ; Kakeru Masaki¹ ; Makoto Nanko¹ ; Masatoshi Takeda¹ ; ¹Nagaoka University of Technology, Nagaoka, Japan; ²Nagoya Industrial Science Research Institute, Nagoya, Japan; ³Aichi University of Education, Kariya-shi, Japan; ⁴Riken, Wako, Japan;
Paper Id: 417 [Abstract]

The FLAPW (full-potential linearized augmented plane wave)-Fourier (FF) theory has been developed by Mizutani and Sato and accomplished the development in 2021 [1]. This method can elucidate interaction between the Fermi surface and Brillouin zones when phase stabilities of compounds are discussed based on the extended zone scheme. We have examined compounds having cP12 structures using the FF theory and selected pyrite-type FeS₂ as a candidate of a thermoelectric material so that (1) it has a band gap at the Fermi energy (E_F) as an insulator, (2) itinerant electrons slightly remain near E_F and (3) the conduction and valence band structures at Γ show free electron and tight-binding like behavior, respectively [2].<br />　The thermoelectric properties of FeS₂ have been reported in some literatures. Nevertheless, while the electrical conductivity reveals semiconductor-like behavior; that is, it monotonically increases as the temperature increases, the Seebeck coefficient sometimes shows positive values only at low temperatures or exhibits just positive values in all the measured temperatures. Thus, the transport mechanism in FeS₂ is indeed unclear particularly for the bulk state. Thus, we used plain Fe and S powders and spark plasma sintering to fabricate the FeS₂ compounds and then measured the thermoelectric properties. The results of temperature dependence are compared with those calculated by the Boltzmann transport equation and electronic structure calculations.<br /> Fe and S powders were encapsulated in a Pyrex tube, mixed and heat treated at 625 K for 4 h in Ar atmosphere. However, due to the evaporation of S, the FeS₂ single phase could not be obtained. Then, the heat treatments were subjected to the mixtures several times, and finally pyrite-type FeS₂ had been acquired. The electrical conductivity shows 2 S/cm at room temperature and monotonically increases with increasing temperature. Though the Seebeck coefficient shows positive values at low temperatures below 500 K, it turns back negative values at high temperatures. When the Seebeck coefficient is calculated within a frame work of a constant relaxation time approximation using WIEN2k, all the Seebeck coefficient in the used temperature range gives rise to negative values. The discrepancies between the experimental and theoretical results will be discussed in view of the material preparation method , defects or effects of electron-phonon interactions.

References:
[1] U. Mizutani, H. Sato, T.B. Massalski, Prog. Mater. Sci. 120 (2021) 100719.\n[2] T. Homma, U. Mizutani, H. Sato, Phil. Mag. 100 (2019) 426-455.