“…As one of the typical Zintl phases, Yb 14 MnSb 11 has received wide attention not only due to its high TE performance but also because of its unique low-temperature magnetic and electronic properties. [261][262][263][264][265][266][267][268][269][270][271][272][273][274][275][276][277][278] This compound is isostructural to Ca 14 AlSb 11 and crystallises in the space group of I4 1 /a (Fig. 24a).…”
Section: Zintl Phasesmentioning
confidence: 99%
“…262 Alloying (solid solution) approaches have been used to optimise TE properties of Yb 14 MnSb 11 . Solid solutions, such as Yb 14 Mn 1− x Zn x Sb, 264 Yb 14 Mn 1− x Al x Sb, 65,265 Yb 14 MnSb 11− x Te x , 266 Yb 14 MnSb 11− x Ge x , 267 Yb 14− x Ca x MnSb 11 , 34,268,269 Yb 14− x Ce x MnSb 11 , 270 Yb 14− x Ln x MnSb 11 (Ln = La, 261,271 Tm 272,273 and Lu 274 ), Yb 14− x RE x MnSb 11 (RE = Pr and Sm), 275 show zT values in the range of about 1.1–1.3 at high temperatures (Fig. 24 b ). Figure 24 a Body-centred, I4 1 /acd crystal structure of Yb 14 MnSb 11 .…”
Thermoelectric (TE) materials facilitate direct heat-to-electricity conversion. The performance of a TE material is characterised by its figure of merit zT (=S 2 σT/κ) that depends on both electronic transport properties, i.e. the Seebeck coefficient S and the electrical conductivity σ, and on thermal transport properties, i.e. the thermal conductivity κ of a material. The intrinsically countercorrelated behaviour between electronic and thermal transport properties makes the enhancement of zT a very challenging task. In the past 10 years, the zTs in bulk TE materials have been significantly enhanced due to intensive exploratory efforts, the discovery of new physical phenomena and effects, and applications of advanced synthesis methods. In this review, we summarise the recent progress in bulk TE materials. After the introduction of fundamental principles of thermoelectricity, the recently achieved enhancements in the TE performance encompassing the use of electronic band structure engineering, lattice phonon engineering and nanostructure tailoring will be emphasised. Next, the highlights of typical TE materials will be presented, focusing especially on the great progress achieved during the past decade. Finally, new techniques and approaches developed to fabricate TE materials will be outlined and their impact on the performance and economic viability of large-scale TE applications will be considered. The progress made during the past dozen or so years provides great opportunities for the use of bulk TE materials in a much broader range of applications and bodes well for a more efficient utilisation of energy.
“…As one of the typical Zintl phases, Yb 14 MnSb 11 has received wide attention not only due to its high TE performance but also because of its unique low-temperature magnetic and electronic properties. [261][262][263][264][265][266][267][268][269][270][271][272][273][274][275][276][277][278] This compound is isostructural to Ca 14 AlSb 11 and crystallises in the space group of I4 1 /a (Fig. 24a).…”
Section: Zintl Phasesmentioning
confidence: 99%
“…262 Alloying (solid solution) approaches have been used to optimise TE properties of Yb 14 MnSb 11 . Solid solutions, such as Yb 14 Mn 1− x Zn x Sb, 264 Yb 14 Mn 1− x Al x Sb, 65,265 Yb 14 MnSb 11− x Te x , 266 Yb 14 MnSb 11− x Ge x , 267 Yb 14− x Ca x MnSb 11 , 34,268,269 Yb 14− x Ce x MnSb 11 , 270 Yb 14− x Ln x MnSb 11 (Ln = La, 261,271 Tm 272,273 and Lu 274 ), Yb 14− x RE x MnSb 11 (RE = Pr and Sm), 275 show zT values in the range of about 1.1–1.3 at high temperatures (Fig. 24 b ). Figure 24 a Body-centred, I4 1 /acd crystal structure of Yb 14 MnSb 11 .…”
Thermoelectric (TE) materials facilitate direct heat-to-electricity conversion. The performance of a TE material is characterised by its figure of merit zT (=S 2 σT/κ) that depends on both electronic transport properties, i.e. the Seebeck coefficient S and the electrical conductivity σ, and on thermal transport properties, i.e. the thermal conductivity κ of a material. The intrinsically countercorrelated behaviour between electronic and thermal transport properties makes the enhancement of zT a very challenging task. In the past 10 years, the zTs in bulk TE materials have been significantly enhanced due to intensive exploratory efforts, the discovery of new physical phenomena and effects, and applications of advanced synthesis methods. In this review, we summarise the recent progress in bulk TE materials. After the introduction of fundamental principles of thermoelectricity, the recently achieved enhancements in the TE performance encompassing the use of electronic band structure engineering, lattice phonon engineering and nanostructure tailoring will be emphasised. Next, the highlights of typical TE materials will be presented, focusing especially on the great progress achieved during the past decade. Finally, new techniques and approaches developed to fabricate TE materials will be outlined and their impact on the performance and economic viability of large-scale TE applications will be considered. The progress made during the past dozen or so years provides great opportunities for the use of bulk TE materials in a much broader range of applications and bodes well for a more efficient utilisation of energy.
“…[72][73][74] The solid solution, Yb14-xCaxMnSb11 has also been studied in order to investigate the thermoelectric properties. [75][76][77] More recently, the solid solutions of the A site have focused on RE (rare earth) substitutions. 31,[59][60][61][62][63][64][65][66]78 As mentioned above, the rare earth elements in the 3+ oxidation state (RE) show site preferences that depend upon size.…”
Yb14MnSb11 is a member of a remarkable structural family of compounds that are classified according to the concept of Zintl. This structure type, of which the prototype is Ca14AlSb11, provides a flexible framework for tuning structure-property relationships and hence the physical and chemical properties of compounds. Compounds within this family show exceptional high temperature thermoelectric performance at temperatures above 300 K and unique magnetic and transport behavior at temperatures below 300 K. This review provides an overview of the structure variants, the magnetic properties, and the thermoelectric properties. Suggestions for directions of future research are provided. One active research area is to systematically explore more complex compositions such as Ca11Sb10, K4Pb9, Na8Si46, Ca14AlSb11 and KBa2InAs3. 3-7 The other direction is to replace the alkaline earth metals with divalent rare earth elements (Sm, Eu and Yb) along with the introduction of transition metals into structures, typically replacing the less electronegative metalloid in the anionic framework. 8-10 Combinations of these two directions led to compounds such as Yb14MnSb11, Pr4MnSb9, Eu10Mn6Sb13, Yb9Zn4+xBi9 and Cs13Nb2In6As10. 11-16 The complexity of compositions can be combined with a small flexibility in electron counting. For example, Yb14MnSb11 and Yb9Zn4+xBi9 do not strictly follow the Zintl-Klemm concept. Yb14MnSb11 has Mn 2+ instead of a group 13 element such as in Ca14AlSb11 and therefore is electron deficient, 17 and Yb9Zn4+xSb9 has interstitial Zn atoms which can be compositionally varied to achieve specific properties. 18 At the same time, the total number of valence electrons within an identical Zintl phase structure type with different elements may also vary slightly but the variance can be quite small and limited for many structure types that can be described by the Zintl concept. Therefore, with the introduction of transition elements, new electronic properties are possible, but complete transfer of electrons and clear counting of valence electrons remains a criterion for describing transition and rare earth metal containing Zintl phase compounds. Binary Zintl phase compounds which have compositions of simple ratios of elements usually adopt the structures of known oxides or halides, in which anions and cations are isolated in the structure with no covalent bonding. 2, 19 Both isolated anions, polyanions or clusters in Zintl phase compounds can provide complex compositions such as those represented by Ca11Sb10 and K4Pb9. 3, 4 Polyanions or clusters are formed to compensate for lack of enough electrons from the electropositive element to satisfy valence to form a simple one atom anion. Sb forms Sb-Sb single bonds in the Ca11Sb10 structure type resulting in Sb2 4and Sb4 2polyanions in the structure. 3 The Zintl electron counting provides the following charge balanced scenario: 11Ca 2+ + 4Sb 3-+ 2Sb2 4-+ Sb4 2-. Two types of clusters exist in K4Pb9 with the same formal oxidation state: a monocapped square antiprism and a tr...
“…20 To improve zT, the substitution of La (for Yb) 21 and Al (for Mn) 22,23 into the system was previously investigated with an aim to reduce the carrier concentration by adding extra electrons to fill the holes. Ca (for Yb) 24,25 and Zn (for Mn) 26 dopings were also studied in order to enhance the thermoelectric properties by introducing mass disorder scattering and removing spin scattering, respectively. Tm (for Yb) was used to provide chemical pressure and enhance the Seebeck coefficient.…”
A series of single crystal samples, Yb 14 MnSb 11Àx Te x (x # 0.2), were investigated via Sn flux. The element distributions were mapped using an electron microprobe, which demonstrated inhomogeneity and limited solubility of Te in the crystals. The magnetic properties of two crystals of compositions Yb 13.80(2) Mn 1.03(1) Sb 11.11(4) Te 0.06(3) and Yb 13.82(3) Mn 1.02(1) Sb 11.02(8) Te 0.14(6) were investigated. Increasing amounts of Te increase the saturation moment of Yb 14 MnSb 11Àx Te x , and slightly lower the ordering temperature T C by about 1 K. This is attributed to the filling of the hole in Yb 14 MnSb 11 and the reduction of the screening of the Mn 2+ d 5 electrons, resulting in a higher effective moment. Hotpressed, fully dense pellets of Yb 13.72(3) Mn 1.08(1) Sb 11.13(6) Te 0.07(5) , Yb 13.76(5) Mn 1.11(1) Sb 10.96(8) Te 0.16(8) , and Yb 13.76(4) Mn 1.10(2) Sb 10.95(9) Te 0.19(7) were prepared for thermoelectric property measurements. Both Seebeck coefficient and electrical resistivity increase with increasing amount of Te as a result of decreasing carrier concentration. Increasing amounts of YbTe with increasing x could be identified in the electron microprobe. The total thermal conductivity was approximately the same for all compositions, similar to that of Yb 14 MnSb 11 . The figure of merit zT reaches a maximum of 1.11 for x ¼ 0.07 at 1240 K, which is approximately 12% higher than the parent compound, Yb 14 MnSb 11 .
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