新穎四元硒化物Pb4BixSb10-xSe19(x = 3.4, 4, 6.6)的合成、鑑定與特性分析

Abstract

本論文使用Pb、Bi、Sb、Se粉末，成功合成出Pb4Bi3.4Sb6.6Se19與Pb4Bi6.6Sb3.4Se19兩個為同型晶體的新穎四元硒化物，空間群為C2/m (No.12)，晶系為monoclinic。前者的晶胞常數為a = 27.982(4) Å、b = 4.123(5) Å、c = 21.139(3) Å、β =130.837(5)°、V = 1845.4(4) Å3、Z = 4，所得R值為R1 = 0.0393、wR2= 0.0885；後者的晶胞常數為a = 28.118(2) Å、b = 4.1522(4) Å、c = 21.308(2) Å、β =130.941(5)°、V = 1879.2(3) Å3、Z = 4，所得R值為R1 = 0.0407、wR2= 0.1069。其結構由NaCl100-type [M6Se8]單位與NaCl111-type [M8Se11]單位所組成，形成[M6Se8] [M8Se11]的分子式。 論文使用成功純化出的化合物Pb4BixSb10-xSe19 (x = 3.4, 4)進行物性測量。DTA測量表示2化合物具有2處的主相變化，漫反射吸收光譜指出化合物的光學能隙皆小於0.67 eV，導電度測量結果顯示樣品具有半導體的特性。LMTO則使用了模型Pb4Bi4Sb6Se19與Pb4Bi6Sb4Se19計算化合物的DOS與其中M2-Se鍵結的COHP，Pb4Bi4Sb6Se19的理論能隙為0.45 eV，Pb4Bi6Sb4Se19則為0.50 eV。

New quanternary chalcogenides, Pb4Bi3.4Sb6.6Se19 and Pb4Bi6.6Sb3.4Se19, were synthesized by elements powder of stoichiometric ratios. Single crystal X-ray diffraction studies indicated both isomorphous compounds crystallized in monoclinic space group C2/m (No.12). Crystal data of Pb4Bi3.4Sb6.6Se19 are a = 27.982(4) Å, b = 4.123(5) Å, c = 21.139(3) Å, β =130.837(5)°, V = 1845.4(4) Å3, Z = 4, R1 = 0.0393 and wR2= 0.0885; crystal data of Pb4Bi6.6Sb3.4Se19 are a = 28.118(2) Å, b = 4.1522(4) Å, c = 21.308(2) Å,β =130.941(5)°, V = 1879.2(3) Å3, Z = 4, R1 = 0.0407 and wR2= 0.1069. These compounds contain the same crystal structure building units with NaCl100-type [M6Se8] and NaCl100-type [M8Se11]. Formulas of compounds are [M6Se8][M8Se11]. Thesis displayed physical properties of successfully purified compounds, Pb4BixSb10-xSe19 (x = 3.4, 4), in following measurements. DTA measurement exhibited that two compounds both had 2 endothermic peaks. UV-visible diffused reflectance spectra suggested optical band gaps less then 0.67 eV for both phases. Electrical conductivity measurements indicated semiconducting behaviors. Electronic structure calculations based on the LMTO method revealed band gaps 0.45 eV and 0.50 eV for model structures of Pb4Bi4Sb6Se19 and Pb4Bi6Sb4Se19, respectively.