First Quaternary A−Pb−Bi−Q (A = K, Rb, Cs; Q = S, Se) Compounds:  Synthesis, Structure, and Properties of α- and β-CsPbBi₃Se₆, APbBi₃Se₆, (A = K, Rb), and APbBi₃S₆ (A = Rb, Cs)

Abstract

α-CsPbBi3Se6 (I), β-CsPbBi3Se6 (II), RbPbBi3Se6 (III), KPbBi3Se6 (IV), CsPbBi3S6 (V), and RbPbBi3S6 (VI) were synthesized by the polychalcogenide flux method. α-CsPbBi3Se6 was obtained at 720 °C and crystallizes in the space group Pnma (no. 62) with a = 23.564(6) Å, b = 4.210(2) Å, c = 13.798(3) Å at room temperature. Final R/R w = 3.0/3.6%. In this compound, parallel NaCl-type Pb/Bi/Se columns with rectangularly shaped cross-sections are interconnected by edge sharing to build a 3-D tunnel framework with Cs atoms located inside the tunnels. The hexagonal plates of β-CsPbBi3Se6 were obtained at 400 °C and crystallize in the space group P63/mmc (no. 194) with a = 4.213(2) Å, c = 25.22(1) Å, γ = 120° at −100 °C. Final R/R w = 4.2/4.7%. APbBi3Se6 (A = Rb, K) and APbBi3S6 (A = Cs, Rb) are isostructural with β-CsPbBi3Se6 and their hexagonal cell parameters were obtained at room temperature. The structure is composed of negatively charged Bi2Te3-type bilayers separated by alkali metals, which are distributed over two different crystallographic sites. The alkali metal ions are loosely packed in the interlayer space making them mobile. Topotactic ion-exchange reactions of two compounds, β-CsPbBi3Se6 and RbPbBi3Se6, were examined with LiI and NaI in the solid state and in aqueous solution. Prolonged water contact of the hexagonal compounds leads to decomposition and leaching of alkali metal and Pb2+ ions. Electrical conductivity and thermopower measurements for single crystals of I, II, and III show n-type semiconductor behavior with 0.6, 0.3, and 0.3 S/cm and −730, −550, and −560 μV/K at room temperature, respectively. The optical band gaps of all compounds range from 0.27 to 0.89 eV. Thermal properties of the compounds are reported.

Structure and Thermoelectric Properties of the New Quaternary Bismuth Selenides A1−xM4−xBi11+xSe21 (A=K and Rb and Cs; M=Sn and Pb)—Members of the Grand Homologous Series Km(M6Se8)m(M5+nSe9+n)

“…Therefore, we expect these compounds to be sensitive to doping and work to improve the charge transport properties is in progress. The Seebeck coefficients found here are significantly smaller than those of RbPbBi 3 Se 6 (À 560 mV K À1 ) and b-CsPbBi 3 Se 6 (À 550 mV K À1 ), [9] and this is consistent with the higher electrical conductivity. The negative values indicate n-type behavior with electrons as the dominant charge carriers.…”

“…The electrical conductivity of these selenides is four orders of magnitude higher than that of the quaternary lead ± bismuth selenides, RbPbBi 3 Se 6 and bCsPbBi 3 Se 6 (both 0.3 Scm À1 at room temperature), described earlier. [9] The observed temperature dependencies are similar in all four analogues consistent with the behavior of a degenerately doped semi-metal or a narrow band-gap semiconductor.…”

“…According to valence-bond calculations the Bi1 ± 4, Bi6 and Pb1 sites are most likely to have mixed Bi and Pb occupancies. The results of the structure refinement and other crystallographic data are given inTables 2,9,and 10. Further details on the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany (fax: ( 49) 7247-808-666; e-mail: crysdata@fiz-karlsruhe. de), on quoting the depository numbers CSD-411653 (Cs 0.65 Pb 3.65 Bi 11.35 Se 21 ), CSD-411654 (K 1.46 Pb 3.08 Bi 11.46 Se 21 ), CSD-411655 (K 0.54 Sn 3.54 Bi 11.46 Se 21 ) and CSD-411656 (Rb 0.69 Pb 3.69 Bi 11.31 Se 21 ).…”

Alte und neue Konzepte für thermoelektrische Materialien

“…[120] Versuche, den ZT-Wert durch eine Substitution von Sb gegen Sn zu erhöhen, blieben erfolglos. [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.…”

Waste Thermal Energy Harvesting (I): Thermoelectric Effect

“…Some of the new compounds include KBi 3 S 5 [66], KBi 6.33 S 10 [67,68], K 2 Bi 8 S 13 [67,68], a-, b-K 2 Bi 8 Se 13 [69,70], K 2.5 Bi 8.5 Se 14 [70], A x Bi 4 Se 7 [71] (x = 1, 2), BaBiTe 3 [72], CsBi 4 Te 6 [73], ALn 1-x Bi 4-x S 8 [74] (A = K, Rb and Ln = La, Ce, Pr, Nd), BaLa-Bi 2 Q 6 [75] (Q = S, Se), a-, b-APbBi 3 Se 6 [76] (A = K, Rb, Cs), K 1-x Sn 5-x Bi 11+x Se 22 [77] [82] (M = Sn, Pb). These types of compounds have shown low thermal conductivity, high thermopower, and often high electrical conductivity, with CsBi 4 Te 6 having a ZT value of 0.8 at 225 K [73].…”