前驅物導向新穎四元硒化物Ge7Sb18In6Se41與Ge6Sb8Bi4Se23的合成、晶體結構與熱電性質分析

Precursor Dependent Synthesis, Crystal Structure and Thermoelectric Properties of two Novel Quaternary Selenides Ge7Sb18In6Se41 and Ge6Sb8Bi4Se23

王俊智(Chun-Chih Wang)

指導教授 ： 李積琛

國立交通大學/理學院/應用化學系所/碩士(2020年)

摘要

本論文利用本實驗室研發之新穎三元相硒化物GeSb2Se3當作前驅物與已知二元相固態化合物反應並分析其產物，其中最成功的例子為γ-In2Se3及Bi2Se3，我們在產物中發現兩新穎四元相硒化物Ge7In6Sb18Se41及Ge6Bi4Sb8Se23，此二化合物之晶系皆為單斜晶系，空間群分別為Cm與Pm，晶胞常數分別為a = 31.1311(11) Å、b =3.9906(1) Å、c = 29.9362(10) Å、β =95.434(1)°及a = 21.1702(15) Å、b =4.0457(3) Å、c = 25.8821(17) Å、β =100.241(3)°。
兩者之結構皆具有NaCl100-type及NaCl111-type兩種型式的構造單元，其中NaCl100-type皆由[Sb1+2M3+11Se2-15]單元組成且都包含獨特的Sb-Sb鍵結之ㄧ維結構，而NaCl111-type則是分別由[M2+/3+18Se2-26](M=Ge/In/Sb)、[M2+/3+23Se2-31] (M=Ge/Bi/Sb)單元所組成。
兩化合物皆必需使用GeSb2Se3與已知二元相硒化物（γ-In2Se3、Sb2Se3 或Bi2Se3、GeSe）作為反應起始物，依比例於773 K合成，重要的是其皆無法由元素態反應得到純相。兩化合物的X光電子能譜(XPS)顯示皆有低價態的Sb存在於結構中，電阻值皆隨溫度上升而下降，且Seebeck係數皆為負值，顯示其為n型半導體，能隙分別約為0.3 eV及0.03 eV，符合漫反射光譜之結果。
理論計算之能態密度(DOS)與能帶結構(Band Structure)顯示兩者為間接能隙半導體。兩化合物皆具有較低的導熱度，且都低於商業用的熱電材料Bi2Te3、PbTe及CsBi4Te6，而兩者之ZT值則分別為7.92×10-6及0.037。

關鍵字

硫族化合物 ； 層狀結構 ； 熱電材料 ； 固態化學 ； 前驅物 ； 同系物系

並列摘要

Two novel quaternary selenides Ge7In6Sb18Se41(1) and Ge6Bi4Sb8Se23(2) were synthesized from a solid state reaction using precursors of GeSb2Se3 and γ-In2Se3, Bi2Se3. 1 and 2 adopt monoclinic cell space group Cm and Pm, with the cell dimensions a = 31.1311(11) Å, b =3.9906(1) Å, c = 29.9362(10) Å, β =95.434(1) ° and a = 21.1702(15) Å, b =4.0457(3) Å, c = 25.8821(17) Å, β =100.241(3) °.
They consist two kinds of building units, NaCl111-type [M2+/3+18Se2-26], [M2+/3+23Se2-31] (M = Ge/In or Bi/Sb) and NaCl100-type [Sb1+2M3+11Se2-15] [(M = Ge/Sb), (M=Ge/Bi/Sb)]. Interestingly, the 1D unit [Sb1+2M3+11Se2-15] contains a unique Sb-Sb chain.
Pure phases of 1 and 2 can not be synthesized by combining constituent elements, they were only be prepared by precursors of GeSb2Se3, γ-In2Se3, Bi2Se3, Sb2Se3 and GeSe at 773 K. X-ray photoelectron spectroscopy (XPS) indicated Sb cation contains low oxidation states, they are semiconductors with indirect band gaps of 0.03 eV and 0.3 eV, which is in consistent with DFT calculations, Electrical conductivity, Diffuse reflectance spectroscopy and Seebeck coefficient show n-type semiconducting properties.
The complex crystal structures lead to the reducing thermal conductivities for 1 and 2, which are significantly lower than the commercial materials Bi2Te3, PbTe and CsBi4Te6. The figure of merit (ZT) at 435 K for 1 and 2 are 7.92×10-6 and 0.037.

並列關鍵字

Chalcogenides ； Layered structure ； Thermoelectric materials ； Solid state chemistry ； Precursors ； Homologous series

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