High thermopower and low thermal conductivity in semiconducting ternary K-Bi-Se compounds.: Synthesis and properties of β-K2Bi8Se13 and K2.5Bi8.5Se14 and their Sb analogues
High thermopower and low thermal conductivity in semiconducting ternary K-Bi-Se compounds.: Synthesis and properties of β-K2Bi8Se13 and K2.5Bi8.5Se14 and their Sb analogues
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DOI：
10.1021/cm970397e
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发表时间：
1997-12-01
影响因子：
8.6
通讯作者：
Kanatzidis, MG
中科院分区：
文献类型：
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作者：
Chung, DY;Choi, KS;Kanatzidis, MG
用熔融法合成了β-K2Bi8Se13(I)、K2Sb8Se13(II)、K2.5Bi8.5Se14(III)和K2.5Sb8.5Se14(IV)。化合物I的黑针在600℃下形成，结晶为单斜晶系P2(1)/m空间群(11号)，a=17.492(3)Angstrom，b=4.205(1)Angstrom，c=18.461(4)Angstrom，β=90.49(2)°。最终R/R-w=6.7/5.7%。化合物II与I是同构的，I和II都是与K2Bi8S13同构的，K2Bi8S13是由氯化钠、Bi2Te3-和CdI2类型的单元连接而成的K+填充通道。在530℃下获得的III型和TV型黑色细针分别为a=17.534(4)埃，b=4.206(1)埃，c=21.387(5)埃，β=109.65(2)度和a=17.265(3)埃，b=4.0801(9)埃，c=21.280(3)埃，a=4.0801(1)埃，c=21.280(3)埃。最终R/R-w=6.3/8.3%和5.1/3.6%。化合物III和TV是等结构的，钾和铋/锑原子在两个结晶学位置上是无序的。电导率和热电势测量表明，在室温下，I单晶的电导率和热电导接近250MU/cm，V/K接近200mV/K；多晶Ⅲ的电导率和热电性接近150MV/cm和100MU V/K。探讨了真空退火对这些化合物的影响。所有化合物的光学带隙分别为0.59、0.78、0.56和0.82 eV。本文报道了熔融生长的I和III多晶锭的导热系数。
beta-K2Bi8Se13 (I), K2Sb8Se13 (II), K2.5Bi8.5Se14 (III), and K2.5Sb8.5Se14 (IV) were synthesized by a molten flux method. The black needles of compound I were formed at 600 degrees C and crystallized in the monoclinic P2(1)/m space group (No. 11) with a = 17.492(3) Angstrom, b = 4.205(1) Angstrom c = 18.461(4) Angstrom, beta = 90.49(2)degrees. The final R/R-w = 6.7/5.7%. Compound II is isostructural to I. Both I and II are isostructural with K2Bi8S13 which is composed of NaCl-, Bi2Te3-, and CdI2-type units connecting to form K+-filled channels. The thin black needles of III and TV obtained at 530 degrees C crystallize in the same space group P2(1)/m with a = 17.534(4) Angstrom, b = 4.206(1) Angstrom, c = 21.387(5) Angstrom, beta = 109.65(2)degrees and a = 17.265(3) Angstrom, b = 4.0801(9)Angstrom, c = 21.280(3) Angstrom, beta = 109.31(1)degrees, respectively. The final R/R-w = 6.3/8.3% and 5.1/3.6%. Compounds III and TV 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 similar to 250 S/cm and similar to 200 mu V/K for a single crystal of I and similar to 150 S/cm and similar to 100 mu V/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 I and III are reported.