含鉍之新穎熱電材料的合成與分析

Abstract

本實驗使用Sn、In、Bi和Se元素在1073 K下合成新化合物Sn4.89In2Bi5.11Se16，並且使用單晶繞射解出結構。此晶體之空間群C 2/m，晶胞常數為a = 13.530(3) Å、 b = 4.1208(8) Å、c = 15.255(3) Å、β = 115.70(3)°、 V = 766.4(3) Å3、 Z = 1，晶系是屬於monoclinic，最後所得之R值為R1 = 0.0437 、 wR2 = 0.1175。Sn4.89In2Bi5.11Se16的結構由平行a軸的無限個類似NaCl形式之塊狀單元組成，塊狀單元彼此間由鍵長2.941(2) Å之Bi-Se鍵連接而成三度空間立體結構。 以Sn4In2Bi6Se16模型理論計算所得之DOS與Band圖，顯示此化合物是具有狹窄的能隙的半導體。由四點探針法測量電阻率，發現電阻率在298-393 K範圍內隨溫度上升而下降，具有半導體性質與理論計算結果相符。Seebeck值在300-700 K範圍內平均為-544μV/K，是屬於N型半導體。室溫下的 power factor為1.6854 μW/cmK2。初步的研究發現，當改變Sn、Bi含量比例時，室溫下的Seebeck值隨Sn增加而由-424 μV/K逐漸變為350 μV/K。

A new quaternary compound of Sn4.89In2Bi5.11Se16 was synthesized by direct combination of the Sn:In:Bi:Se = 4:3:7:18 at temperature at 1073 K. The structure was determined by single-crystal X-ray diffraction. The compound crystallized in the monoclinic space group C2/m with a = 13.530(3) Å, b = 4.1208(8) Å, c = 15.255(3) Å, β = 115.70(3)°, V = 766.4(3) Å3, and Z = 1. The final R values are R1 = 0.0437 and wR2 = 0.1175. The structure of Sn4.89In2Bi5.11Se16 features three-dimenssional framework consisting of wide rectangular NaCl-type infinit rod type unit running parallel to the a-axis, which are stitched together by Bi-Se at a distance of 2.941(2) Å. Theoretical study base on the model compound of Sn4In2Bi6Se16 using density of state and band structure analyses suggests that the material is a narrow band gap semiconductor. The four probe electroconductivity measurements in temperature range between 298-393 K show decline of the resistivity of Sn4.89In2Bi5.11Se16 with increase of temperature. Thermopower of Sn4.89In2Bi5.11Se16 is ~-544μV/K over temperature range between 300 and 700 K, which indicats n-type semiconducting property. The room temperature power factor of Sn4.89In2Bi5.11Se16 is 1.6854 μW/cmK2. Preliminary studies on the effect of relative composition of Sn and Bi to thermopower indicate that the average thermopower is varied between -424 and 350μV/K at room temperature.