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)

Abstract

Several members of the new family A(1-x)M(4-x)Bi(11+x)Se21 (A = K, Rb, Cs; M = Sn, Pb) were prepared by direct combination of A2Se, Bi2Se3, Sn (or Pb), and Se at 800 degrees C. The single-crystal structures of K(0.54)Sn(3.54)Bi(11.46)Se21, K(1.46)Pb(3.08)Bi(11.46)Se21, Rb(0.69)Pb(3.69)Bi(11.31)Se21, and Cs(0.65)Pb(3.65)Bi(11.35)Se21 were determined. The compounds A(1-x)M(4-x)Bi(11+x) Se21 crystallize in a new structure type with the monoclinic space group C2/m, in which building units of the Bi2Te3 and NaCl structure type join to give rise to a novel kind of three-dimensional anionic framework with alkali-ion-filled tunnels. The building units are assembled from distorted, edge-sharing (Bi,Sn)Se6 octahedra. Bi and Sn/Pb atoms are disordered over the metal sites of the chalcogenide network, while the alkali site is not fully occupied. A grand homologous series Km(M6Se8)m(M(5+n)Se(9+n)) has been identified of which the compounds A(1-x)M(4-x)Bi(11+x)Se21 are members. We discuss here the crystal structure, charge-transport properties, and very low thermal conductivity of A(1-x)M(4-x)Bi(11+x)Se21.

Search for New Thermoelectric Materials through Exploratory Solid State Chemistry. The Quaternary Phases A1+xM3−2xBi7+xSe14, A1−xM3−xBi11+xSe20, A1−xM4−xBi11+xSe21 and A1−xM5−xBi11+xSe22 (A = K, Rb, Cs, M = Sn, Pb) and the Homologous Series Am[M6Se8]m[M5+nSe9+n]

“…Those sites that are primarily occupied with Bi atoms have distorted octahedral geometry, the other sites involving A atoms can be of higher coordination. x M 3-x Bi 11+x Se 20 these blocks are three M octahedra wide and one octahedron high and therefore very similar to those found in A 1-x M 4-x Bi 11+x Se 21 [7] and A 1-x M 5-x Bi 11+x Se 22 [8] (see Figure 3) Figure 2. The structures depicted in Figure 3 possess the same [M 8 Se 12 ] NaCl 111 -type unit (n=1).…”

“…[3], [4] show that such exploratory investigations can lead to promising new thermoelectric materials. Naturally, we enlarged our investigations to quaternary systems of the type A/M/Bi/Se (A = K, Rb, Cs, M= Pb, Sn) and identified new materials such as A 1+x M 3-2x Bi 7+x Se 14 , [5] K 1+x Sn 4-2x Bi 7+x Se 15 , [6] K 1-x Sn 4-x Bi 11+x Se 21 , [7] K 1-x Sn 5-x Bi 11+x Se 22 , [8] , which have structures closely related to each other and to those of β-K 2 Bi 8 Se 13 and K 2.5 Bi 8.5 Se 14 . [9] It turns out they are all members of a newly identified grand homologous series A m [M 6 Se 8 ] m [M 5+n Se 9+n ] [7] (M = di-and valent metal) in both compositional and structural sense.…”

Low lattice thermal conductivity in Pb5Bi6Se14, Pb3Bi2S6, and PbBi2S4: promising thermoelectric materials in the cannizzarite, lillianite, and galenobismuthite homologous series

“…[23][24][25][26] Therefore, in such homologous compounds, the thermoelectric properties can be tuned by modifying the structural module(s). In the past decade, several homologous layered structures including A m [M 0 1+l Se 2+l ] 2m [M 0 0 2l+n Se 2+3l+n ] (A ¼ alkali and alkali earth element; M 0 and M 00 ¼ the main group element), [27][28][29][30][31][32][33][34][35][36][37][38] Cs 4 [Bi 2n+4 Te 3n+6 ], 28,[39][40][41] CsM m Bi 3 Te 5+m , 42,43 and tetradymite homologous series [MTe] n [Bi 2 Te 3 ] m (M ¼ Ge, Sn, Pb) [44][45][46][47][48][49][50][51][52] have been reported. A record high ZT below room temperature was found in CsBi 4 Te 6 with $0.8 at 225 K. 39 In this study, we assessed for the rst time the high-temperature thermoelectric properties of Pb 5 Bi 6 Se 14 , a member of the cannizzarite homologous series; Pb 3 Bi 2 S 6 , a member of the lillianite homologous series; and PbBi 2 S 4 , a member of the galenobismuthite homologous series.…”

CsPb3Bi3Te8 and CsPb4Bi3Te9: low-dimensional compounds and the homologous series CsPbmBi3Te5 + m

“…1 These attributes can lead to high power factors and low thermal conductivity both necessary to achieve a high figure of merit. [2][3][4][5][6][7] Recently, we reported the phase CsBi 4 Te 6 , which when properly doped can reach a high thermoelectric figure of merit below room temperature. 8 In an effort to produce new materials that resemble CsBi 4 Te 6 , we introduced Pb metal into its layered framework and searched for corresponding quaternary phases.…”