Year: 2018
Type: article
Abstract: Two new layered compounds Rb 2 ZnBi 2 Se 5 and Cs 6 Cd 2 Bi 8 Te 17 are described. Rb 2 ZnBi 2 Se 5 crystallizes in the orthorhombic space group Pnma, with lattice parameters of a = 15.6509(17) Å, b = 4.218(8) Å, and c = 18.653(3) Å. Cs 6 Cd 2 Bi 8 Te 17 crystallizes in the monoclinic C 2/ m space group, with a = 28.646(6) Å, b = 4.4634(9) Å, c = 21.164(4) Å, and β = 107.65(3)°. The two structures are different and composed of anionic layers which are formed by inter connecting of BiQ 6 octahedra (Q = Se or Te) and MQ 4 (M = Zn or Cd) tetrahedra. The space between the layers hosts alkali metal as counter cations. The rubidium atoms of Rb 2 ZnBi 2 Se 5 structure can be exchanged with other cations (Cd 2+, Pb 2+ and Zn 2+ ) in aqueous solutions forming new phases. Rb 2 ZnBi 2 Se 5 is an n -type semiconductor and exhibits an indirect band gap energy of 1.0 eV. Rb 2 ZnBi 2 Se 5 is a congruently melting compound (mp ∼644 °C). The thermal conductivity of this semiconductor is very low with 0.38 W·m –1 ·K –1 at 873 K. Density functional theory (DFT) calculations suggest that the low lattice thermal conductivity of Rb 2 ZnBi 2 Se 5 is attributed to heavy Bi atom induced slow phonon velocities and large Gruneisen parameters especially in the a and c directions. The thermoelectric properties of Rb 2 ZnBi 2 Se 5 were characterized with the highest ZT value of ∼0.25 at 839 K.
Source: Inorganic Chemistry
Authors: Jing Zhao, Shiqiang Hao, Saiful M. Islam, Haijie Chen, Shulan Ma, Chris Wolverton, Mercouri G. Kanatzidis
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2883466287