Magnetic Full-Heusler Compounds for Thermoelectric Applications

Abstract

Full-Heusler compounds exhibit a variety of magnetic properties such as non-magnetism, ferromagnetism, ferrimagnetism and anti-ferromagnetism. In recent years, they have attracted significant attention as potential thermoelectric (TE) materials that convert thermal energy directly into electricity. This chapter reviews the theoretical and experimental studies on the TE properties of magnetic full-Heusler compounds. In Section 1, a brief outline of TE power generation is described. Section 2 introduces the crystal structures and magnetic properties of full-Heusler compounds. The TE properties of full-Heusler compounds are presented in Sections 3 and 4. The relationship between magnetism, TE properties and order degree of full-Heusler compounds is elaborated.

Effects of Disorder on the Electronic Structure and Thermoelectric Properties of an Inverse Full-Heusler Mn2CoAl Alloy

“…23 Although Mn 2 CoAl was reported to have a Seebeck coefficient of nearly 0 μV K −1 from 1.8 to 350 K, 24 a theoretical calculation predicted that the spin-gapless semiconducting Mn 2 CoAl can achieve a high S ∼ ±100 μV K −1 by tuning the position of E F . 19 Partial substitution can change the position of E F , leading to increased hole and electron carrier concentration in Mn 2 CoAl. Therefore, we have carried out partial substitution of Si for Al in Mn 2 CoAl to increase the electron carrier concentration and obtain favorable TE properties in Mn 2 Co(Al 1−x Si x ) materials.…”

“…In recent years, thermoelectric (TE) materials with a unique electronic structure have attracted intense interest because they can potentially overcome the limitations and trade-offs encountered in the enhancement of TE properties. − In particular, full-Heusler or inverse full-Heusler alloys have become a new research direction in TE material research. − Some of these materials are either half-metals or spin-gapless semiconductors. These types of electronic structures show unique properties: a half-metal has a metallic electronic structure in one of the two spin bands and a semiconducting electronic structure in the other spin band, while in a spin-gapless semiconductor, the valence band and the conduction band are in contact with each other at the Fermi level ( E F ) in one spin band, whereas a band gap exists at E F in the other spin band .…”

“…These types of electronic structures show unique properties: a half-metal has a metallic electronic structure in one of the two spin bands and a semiconducting electronic structure in the other spin band, while in a spin-gapless semiconductor, the valence band and the conduction band are in contact with each other at the Fermi level ( E F ) in one spin band, whereas a band gap exists at E F in the other spin band . In previous studies, we have investigated the TE properties of half-metallic full-Heusler alloys ,,, and found that Co 2 MnSi and Mn 2 VAl exhibited a high power factor, PF (= σ S 2 ), where σ and S are the electrical conductivity and Seebeck coefficient, respectively.…”

“…In this study, we focus on an inverse full-Heusler Mn 2 CoAl alloy that is considered to be a spin-gapless semiconductor . Although Mn 2 CoAl was reported to have a Seebeck coefficient of nearly 0 μV K –1 from 1.8 to 350 K, a theoretical calculation predicted that the spin-gapless semiconducting Mn 2 CoAl can achieve a high S ∼ ±100 μV K –1 by tuning the position of E F . Partial substitution can change the position of E F , leading to increased hole and electron carrier concentration in Mn 2 CoAl.…”

Realizing p-type Mg2Sn Thermoelectrics via Ga-Doping and Point Defect Engineering

“…Thermoelectric (TE) materials have attracted increasing attention because they can directly convert waste heat to electricity via the Seebeck effect. − The performance of a TE material is related to its energy conversion efficiency and is generally gauged by the dimensionless figure of merit, zT = S 2 σ T /κ tot , where S , σ, T , and κ tot denote the Seebeck coefficient, electrical conductivity, absolute temperature, and total thermal conductivity, respectively. κ tot is the sum of the electronic thermal conductivity (κ el ), bipolar thermal conductivity (κ bip ), and lattice thermal conductivity (κ lat ).…”