Advances in Thermoelectric Mg₃Sb₂ and Its Derivatives

Abstract

approaching their minimum, therefore fundamentally limits the availability for further improvements in these materials by this thermal strategy.This inspires the development of electronic strategies for zT enhancements in recent years. The strong coupling effect among S, σ, and κ e has led early strategies for electronic performance enhancement to mainly rely on the carrier concentration (n H ) optimization through chemical doping for nearly the past half of a century. [7] Till very recently, proven electronic strategies have been typified by engineering the band structure to increase the band degeneracy through band convergence [8] or nestification, [9] to decrease the band effective mass [10] and to introduce resonant states. [11] These approaches successfully decouple the strong correlation among electronic transport properties to some extent, enabling effective improvements in electronic performance for enhancing zT.The utilization of the above thermal and electronic strategies has led to a significant advancement mostly in conventional thermoelectrics such as PbTe [7,[12][13][14][15][16] and Bi 2 Te 3 , [17][18][19][20] while the toxicity and the scarcity of the constituent element are important issues limiting their large-scale application. Zintl compounds, which by strict definition requires to be valence balanced and semiconducting, [21] have shown excellent zT at high temperatures. [21][22][23][24] A recently developed class of Zintl compounds [25] having CaAl 2 Si 2 -type structure, Mg 3 Sb 2 , and its derivatives, demonstrates a great potential to address the toxicity and the scarcity issues and therefore attracts increasing number of researchers to focus on these materials. [26] The promising thermoelectric performance realized in these compounds is enabled by the richness in composition for further manipulation of both electronic and thermal properties as well as by the intrinsic low lattice thermal conductivity. The general formula for this class of Zintl compounds can be written as AB 2 C 2 , where A can be alkaline earth or rare-earth elements (e.g., Mg, [27][28][29] Ca, [30] Sr, [31,32] Ba, [33] Eu, [34] Yb [30] ), B can be transition metals or main-group elements (e.g., Cd, [35,36] Zn, [37] Mg, [38,39] Mn, [40] Al [41] ), and C can be Group IV/V elements (e.g., Sb, [29] Bi [42] ). Such a broad variety in composition enables either a very low lattice thermal conductivity [43][44][45][46] or a very high band degeneracy, [22,44,45] as well as great availabilities for further manipulating the phonon and charge transport properties through the formation of solid solution. [27,47] In this review, Mg 3 Sb 2 and its derivative (AB 2 C 2 ) compounds with demonstrated high thermoelectric performances are focused on. The origins leading to such a high performance are summarized Over the past couple of decades, thermoelectric Mg 3 Sb 2 and its derivatives have attracted increasing attention for thermoelectric applications. This is enabled by the richness in composition for manipulating both electronic and t...

High-Performance Mg 3 Sb 2- x Bi x Thermoelectrics: Progress and Perspective

“…The advances in n -type Mg 3 Sb 2- x Bi x demonstrate a good paradigm of how a new TE material can be rapidly developed and even transferred into the lab-scale module verification by the current TE community. In the past two years, there have been two timely review articles discussing the recent progress of Mg 3 Sb 2 and its derivatives: one is focusing on the design principle with a combination of theory and experiment [ 99 ] and the other on the manipulation of defects and electronic transport properties [ 100 ]. Readers who are interested in more details may refer to these two reviews.…”

Defect Chemistry for N-Type Doping of Mg3Sb2-Based Thermoelectric Materials

“…N-Type Mg 3 Sb 2 -based Zintl compounds are a class of high-performance thermoelectric materials for the midtemperature application, recently discovered. − Compared to the intrinsic p-type Mg 3 Sb 2 , − the high performance of the n-type counterpart is mainly attributed to the excellent electronic conduction transports characterized by larger N V / m * ( N V and m * are the number of valleys and the band effective mass, respectively) . Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 with a peak zT of 1.51 at 716 K was first reported by Tamaki et al, and multiple groups have reported similar results. − The role of excess Mg is to lift the Fermi level up toward the conduction band, and the Fermi level is further improved by Te doping, thus leading to a high n-type carrier concentration of ∼10 19 cm –3 and excellent thermoelectric transports. , …”

Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

“…The low-temperature (<550 K) materials contain group-V alloys, [7] V 2 VI 3 , [8][9][10][11][12] CsBi 4 Te 6 , [13] and α-MgAgSb, [14] etc., in general exhibiting zT values below 1.5. The class of medium-temperature (550-950 K) materials contains many compounds, including IV-VI alloys, such as PbTe, [15,16] SnTe, [17] GeTe, [18] and SnSe, [19] I-V-VI 2 compounds, [20,21] Zintl compounds, [22] filled Skutterudites, [23] Clathrates, [24] Cu 2 Se, [25] and BiCuSeO, [26] to name a few. They normally embrace maximum zT values above 1.5.…”