Synthesis and Thermoelectric Properties of the New Ternary Bismuth Sulfides KBi_6.33S₁₀ and K₂Bi₈S₁₃

Abstract

KBi 6.33 S 10 and K 2 Bi 8 S 13 were synthesized by the direct combination of K 2 S/Bi 2 S 3 at high temperature (>700°C). The reaction of K 2 S/3.3Bi 2 S 3 at 800°C revealed the presence of a new ternary sulfide KBi 6.33 S 10 (I, 92% yield). The shiny, silver polycrystalline material crystallizes in the orthorhombic space group Pnma (No. 62) with a ) 24.05(1) Å, b ) 4.100-(2) Å, c ) 19.44(1) Å, V ) 1917(3) Å 3 , Z ) 4, and d c ) 5.828 g/cm 3 . Data with F o 2 > 3σ(F o 2 ), 862; no. of variables 108, 2θ max 50°. The final R/R w ) 4.3/4.7%. The structure consists of blocks of Bi 2 Te 3 -and CdI 2 -type units that are connected to form a three-dimensional network with K + ions located in the channels that run along the b axis. The same reaction but with a different reactant ratio at 750°C gave the new ternary sulfide K 2 Bi 8 S 13 (II, 94% yield). This compound crystallizes in the monoclinic space group P2 1 /m (No. 11) with a ) 16.818(2) Å, b ) 4.074(5) Å, c ) 17.801(3) Å, ) 90.48(1)°, V ) 1220(2) Å 3 , Z ) 2, and d c ) 5.900 g/cm 3 . Data with F o 2 > 3σ(F o 2 ), 1924; no. of variables 131, 2θ max 50°. The final R/R w ) 7.3/8.2%. The structure of the shiny rodlike crystals is closely related to that of I. As in I, it also consists of Bi 2 Te 3 -and CdI 2 -type fragments that connect to form K + -filled channels. The two potassium atoms and one bismuth atom are disordered over three sites. Electrical conductivity on I show semiconducting behavior with 10 2 S/cm at 300 K. Compound II possesses an electrical conductivity of 10 2 S/cm at 300 K. The optical bandgaps of I and II (0.06-0.24 eV) were estimated by infrared diffuse reflectance measurements. Thermal analysis and thermal conductivity data for I and II are reported. The thermal conductivity of KBi 6.33 S 10 is found to be substantially lower than that of Bi 2 Te 3 . a The estimated standard deviations in the mean bond lengths and the mean bond angles are calculated by the equations σl ) {∑n(lnl) 2 /n(n -1)} 1/2 , where ln is the length (or angle) of the nth bond, l the mean length (or angle), and n the number of bonds.

Alte und neue Konzepte für thermoelektrische Materialien

“…[121] [139] ALn 1AEx Bi 4AEx S 8 [140] (A = K, Rb; Ln = La, Ce, Pr, Nd), BaLaBi 2 Q 6 [141] (Q = S, Se), a-,bAPbBi 3 Se 6 [142] (A = K, Rb, Cs), K 1Àx Sn 5Àx Bi 11+x Se 22 , [143] A 1+x M' 4À2x Bi 7+x Se 15 [144] (A = K, Rb; M' = Sn, Pb), [145] SnBi 4 Se 7 , [146] CdBi 2 S 4 , [147] CdBi 4 S 7 , [147] Cd 2.8 Bi 8.1 S 15 , [147] Cd 2 Bi 6 S 11 , [147] Ba 3 Bi 6.67 Se 13 [148] und Ba 3 MBi 6 Se 13 [148] (M = Sn, Pb) zu nennen. Derartige Verbindungen haben eine niedrige Wärmeleitfähigkeit, hohe Thermokraft und oftmals eine hohe elektrische Leitfähig-keit, [133,134,149,150] Eine der bemerkenswertesten Phasen ist b-K 2 Bi 8 Se 13 , das wegen seiner geringen Wärmeleitfähigkeit und seines relativ hohen Leistungsfaktors interessant ist. [136] Es zeigte sich, dass sich der ZT-Wert dieses Systems durch Dotieren wesentlich verbessern lässt.…”

Synthesis, Crystal, and Electronic Structure of Ba3Sb2Q7 (Q = S, Se)

“…[8][9][10][11][12][13][14][15][16][17] The stereoactive 5s 2 electron lone pair on the Sb atoms plays an important role in the formation of various isolated SbQ x (Q = S, Se) building blocks and in the condensation of such blocks into infinite 1D, 2D, and 3D fragments. [18,19] In some cases, the presence of the electron lone pair results in the formation of non-centrosymmetric crystal structures with non-linear optical properties. [19][20][21][22] Centrosymmetric antimony chalcogenides also exhibit prospective thermoelectric [9,10,[23][24][25] and magnetic properties.…”

Rb4Sn5P4Se20: A Semimetallic Selenophosphate

“…The value of k total increases slightly with temperature, as observed previously in some metal chalcogenide thermoelectric materials containing alkali metals such as A 1+x M 4À2x M' 7+x Se 15 (A = K, Rb; M = Pb, Sn; M' = Bi, Sb) [23] and KBi 6.33 S 10 . [24] The value of k total is the sum of the phonon (lattice vibrations) and electronic contribution. The electronic thermal conductivity k e was calculated using the WiedemannFranz law k e = LsT, assuming the Lorentz number L o = 2.44 10 À8 W W K À2 .…”