Enhanced Thermoelectric Properties of Variants of Tl₉SbTe₆ and Tl₉BiTe₆

Abstract

Tl9BiTe6, a substitution variant of Tl5Te3, is one of the leading midtemperature thermoelectrics and is postulated to exceed ZT = 1 above 450 K when prepared by zone-melting and reach ZT = 0.86 at 560 K after hot-pressing. We have prepared the isostructural series Tl9Sb1–x Te6, Tl9–x Sb1+x Te6, Tl9Bi1–x Te6, and Tl9–x Bi1+x Te6, with x ranging from 0 to 0.05, from the elements in the stoichiometric ratios and determined their thermoelectric properties after hot-pressing. In theory, these tellurides are narrow-gap semiconductors when x = 0, with all elements in common oxidation states, according to (Tl+)9(Sb/Bi)3+(Te2–)6. The as-prepared samples of this 9-1-6 stoichiometry, however, exhibit relatively high electrical conductivity, which decreases with increasing temperature, indicative of the presence of extrinsic charge carriers. The Seebeck coefficient is generally above +100 μV K–1. Decreasing the Sb and Bi content increases the hole carrier concentration and thus increases the electrical conductivity while decreasing the Seebeck coefficient. The best feature of these thermoelectrics is their low thermal conductivity, which is consistently well below 0.7 W m–1 K–1. In combination with reasonable electrical conductivity and a high Seebeck coefficient, high ZT values in excess of 1 can also be achieved via simple hot-pressing after experimental optimization of the carrier concentration via introducing deficiencies on the Bi site. Moreover, the variants with Sb instead of Bi exhibit similar thermoelectric performance, a result of the combination of a better electrical performance and higher thermal conductivity.

Concerted Rattling in CsAg5Te3 Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance

“…As shown in Figure 2C,C sAg 5 Te 3 exhibits moderate power factors (PF = S 2 s)w ith the maximum value of 3.9 mWcm À1 K À2 at 727 K. This value is comparable to those of other thermoelectrics that possess intrinsically low total thermal conductivities (for example,3.9, 5.7, 6.7, 10.1, 8.2, and 12 mWcm À1 K À2 of Ag 9 TlTe 5, [20] Yb 14 MnSb 11, [21] Tl 9 BiTe 6 , [22] b axis of SnSe, [16] a-Cu 2Àx S, [13] and b-Cu 2Àx Se, [12] respectively).…”

Thermoelectric properties of hot-pressed Tl9LnTe6 (Ln=La, Ce, Pr, Nd, Sm, Gd, Tb) and Tl10−xLaxTe6 (0.90⩽x⩽1.05)

“…Electronic structure calculations imply that as x increases in Tl 10Àx La x Te 6 , a transition from metallic (x = 0) to p-doped semiconducting (x < 1) then to n-doped semiconducting (x > 1) behavior is anticipated [16]. Actually, the above mentioned p-n transition has been demonstrated in Tl 9Àx Bi 1+x Te 6 [9]. In the cases studies here, a increases from a = +83 lV K À1 when x = 0.95 to a = +165 lV K À1 when x = 1.05 at 300 K. Even though the specimen with x = 1.05 is expected to be a n-type semiconductor, its positive sign of the Seebeck coefficient indicates hole conduction is dominant in the sample, probably due to defects in the structure, or possible due to small side products not observed in the X-ray diagram, which affect the Tl:La ratio of the main product.…”

“…More specifically, several ternary derivatives of Tl 5 Te 3 are promising as well, like Tl 9 (BinSb)Te 6 [8][9][10] and Tl 4 (SnnPb)Te 3 [11,12] reaching zT values in excess of 1 above 500 K. Another distinguished character of these compounds is their high average atomic masses, which will reduce the atomic vibration frequencies, thereby enabling a low lattice thermal conductivity. Notably, a lattice thermal conductivity below 0.4 W m À1 K À1 was determined in a zone-refined Tl 9 BiTe 6 [10].…”

Effect of alkali cations on two-dimensional networks of two new quaternary thioarsenates (III) prepared by a facile surfactant-thermal method

“…Chalcogenides contain Group 15 elements have been drawing more and more attentions due to their structural diversity [1][2][3][4][5][6], and tremendous potential applications as nonlinear optics [7][8][9], thermoelectric device [10][11][12], ion exchange [13][14][15][16], and photocatalysis [17][18][19]. Thioarsenates(III), a subclass of chalcogenides, typically demonstrate a special structural feature of the stereochemically active 4s 2 lone pair electrons associated with As(III) [1,3].…”