High Thermopower and Low Thermal Conductivity in Semiconducting Ternary K−Bi−Se Compounds. Synthesis and Properties of β-K 2 Bi 8 Se 13 and K 2.5 Bi 8.5 Se 14 and Their Sb Analogues

作者：Duck Young Chung, Kyoung-Shin Choi, Lykourgos Iordanidis, Jon L. Schindler, Paul Brazis, Carl R. Kannewurf, Baoxing Chen, Siqing Hu, Ctirad Uher, Mercouri G. Kanatzidis · 发表于：Chemistry of Materials · 年份：1997 · DOI：10.1021/cm970397e · 被引用次数：148 · 研究领域：Advanced Thermoelectric Materials and Devices、Crystal Structures and Properties、High-pressure geophysics and materials

β-K 2 Bi 8 Se 13 ( I ), K 2 Sb 8 Se 13 ( II ), K 2.5 Bi 8.5 Se 14 ( III ), and K 2.5 Sb 8.5 Se 14 ( IV ) were synthesized by a molten flux method. The black needles of compound I were formed at 600 °C and crystallized in the monoclinic P 2 1 / m space group (No. 11) with a = 17.492(3) Å, b = 4.205(1) Å, c = 18.461(4) Å, β = 90.49(2)°. The final R / R w = 6.7/5.7%. Compound II is isostructural to I . Both I and II are isostructural with K 2 Bi 8 S 13 which is composed of NaCl-, Bi 2 Te 3 -, and CdI 2 -type units connecting to form K + -filled channels. The thin black needles of III and IV obtained at 530 °C crystallize in the same space group P 2 1 / m with a = 17.534(4) Å, b = 4.206(1) Å, c = 21.387(5) Å, β = 109.65(2)° and a = 17.265(3) Å, b = 4.0801(9) Å, c = 21.280(3) Å, β = 109.31(1)°, respectively. The final R / R w = 6.3/8.3% and 5.1/3.6%. Compounds III and IV are isostructural and potassium and bismuth/antimony atoms are disordered over two crystallographic sites. The structure type is very closely related to that of I . Electrical conductivity and thermopower measurements show semiconductor behavior with ∼250 S/cm and ∼−200 μV/K for a single crystal of I and ∼150 S/cm and ∼−100 μV/K for a polycrystalline ingot of III at room temperature. The effect of vaccum annealing on these compounds is explored. The optical bandgaps of all compounds were determined to be 0.59, 0.78, 0.56, and 0.82 eV, respectively. The thermal conductivities of melt-grown polycrystalline ingots of...