High Thermopower and Low Thermal Conductivity in Semiconducting Ternary K-Bi-Se Compounds. Synthesis and Properties of mages/gifchars/beta2.gif" border="0" align="middle

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• 作者：Duck-Young Chung ; Kyoung-Shin Choi ; Lykourgos Iordanidis ; Jon L. Schindler ; Paul W. Brazis ; Carl R. Kannewurf ; Baoxing Chen ; Siqing Hu ; Ctirad Uher ; and Mercouri G. Kanatzidis
• 刊名：Chemistry of Materials
• 出版年：1997
• 出版时间：December 1997
• 年：1997
• 卷：9
• 期：12
• 页码：3060 - 3071
• 全文大小：342K
• 年卷期：v.9,no.12(December 1997)
• ISSN：1520-5002

文摘

mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-K₂Bi₈Se₁₃(I), K₂Sb₈Se₁₃(II),K_2.5Bi_8.5Se₁₄(III), andK_2.5Sb_8.5Se₁₄(IV) were synthesizedby a molten flux method. The black needles of compoundI were formed at 600 mages/entities/deg.gif">C andcrystallized in the monoclinic P2₁/mspace group (No. 11) with a = 17.492(3) Å,b = 4.205(1)Å, c = 18.461(4) Å, mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> = 90.49(2)mages/entities/deg.gif">.The final R/R_w = 6.7/5.7%.Compound II is isostructuralto I. Both I and II areisostructural with K₂Bi₈S₁₃which is composed of NaCl-, Bi₂Te₃-,andCdI₂-type units connecting to form K⁺-filledchannels. The thin black needles of III andIVobtained at 530 mages/entities/deg.gif">C crystallize in the same space groupP2₁/m with a =17.534(4) Å, b =4.206(1) Å, c = 21.387(5) Å, mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> =109.65(2)mages/entities/deg.gif"> and a = 17.265(3) Å, b= 4.0801(9) Å, c = 21.280(3)Å, mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> = 109.31(1)mages/entities/deg.gif">, respectively. The finalR/R_w = 6.3/8.3% and 5.1/3.6%.Compounds IIIand IV are isostructural and potassium and bismuth/antimonyatoms are disordered overtwo crystallographic sites. The structure type is very closelyrelated to that of I. Electricalconductivity and thermopower measurements show semiconductor behaviorwith ~250 S/cmand ~-200 mages/entities/mgr.gif">V/K for a single crystal of I and ~150S/cm and ~-100 mages/entities/mgr.gif">V/K for a polycrystallineingot of III at room temperature. The effect of vaccumannealing on these compounds isexplored. The optical bandgaps of all compounds were determined tobe 0.59, 0.78, 0.56,and 0.82 eV, respectively. The thermal conductivities ofmelt-grown polycrystalline ingotsof I and III are reported.