新穎四元硫鉍鉛礦型結構硒化物的合成與特性鑑定

Abstract

我們使用固態燒合成四元鉍鉛礦型結構硒化物，藉由單晶繞射解析並研究其晶體結構。利用能帶計算與物理性質量測來證明這類化合物均具有半導體性質。 在第一部份中合成出具有相寬的四元化合物Sn3-xPbxBi2Se6 (x = 0 - 0.7)，此結構為Pnma (No. 62)空間群之斜方晶系，與礦物中的硫鉍鉛礦Pb¬3Bi2S6(Lillinite)的結構相似。差異在於接近tropochemical cell-twinning面上之原子並非呈現鏡面對稱，而是滑動對稱。單晶結果顯示，當鉛的含量增加時，原子逐漸往tropochemical cell-twinning面上移動，由理論計算出來的結果顯示，當不是放在tropochemical cell-twinning面上時具有較強的鍵結能與較低的結構總能量。此一結果會影響解晶時所選擇空間群的正確性。 第二部份為具有相寬的四元化合物PbxSn6-xBi2Se9 (x=0 – 4) ，此結構為空間群Cmcm (No. 63)之斜方晶系，與Pb6Bi2S9結構相同。此化合物為NaCl-(311)層狀結構所組成，標示為L(7, 7)，表示攣晶面兩邊各由七層八面體的寬度沿著[010]的方向組成。 第三部份中，Sn2Pb5Bi4Se13 與 Sn8.65Pb0.35Bi4Se15為不具有相寬之四元化合物，其空間群均為C2/m (No.12)斜方晶系。兩者結構上均具有硫鉍鉛礦系列的特性，於同系列的分類法標示分別為L(4, 5)與L (4, 7) 由導電度與理論計算的結果證實具有狹窄能隙之半導體，Sn2Pb5Bi4Se13 和 Sn8.65Pb0.35Bi4Se15的Seebeck係數分別為-80 和178 (μV/K)。 最後，Pb13Sb2.08Bi1.92Se19為新結構的化合物，屬於C2/m (No. 12)空間群之單斜晶系，晶胞常數為a = 14.127(3) Å, b = 4.2625(8) Å, c = 34.477(6) Å, β = 96.329(4)°，最後所得之R值為 R1/wR2/GOF = 0.0351/0.0822/1.045, Pb13Sb2.08Bi1.92Se19有NaCl-(311)層狀結構，於同系列的分類法標示為L(7, 8)。並經由理論計算與導電度、Seebeck係數的量測，證實為具有半導體性質的材料。

In this dissertation, all selenide compounds were synthesized by solid state method. These structures were determined and investigated with X-ray diffraction of single crystals. Calculations of the density of states, measurements of Seebeck coefficient and electrical conductivity confirm that these compounds are p- or n-type semiconductors with a narrow band gaps. Firstly, New ternary and quaternary chalcogenides Sn3-xPbxBi2Se6 (x = 0 - 0.7) were synthesized and crystallize in the orthorhombic space group Pnma (No. 62). The structure for these compounds is related to Pb3Bi2S6 with an atomic position near the cell-twining plane with lillianite homologous series L(4, 4). The ternary phase contains partially occupied Sn site and a quaternary system exhibits a phase width in the range of 0 ≦ x ≦ 0.7. Single-crystal structure analysis indicates that there is a correlation between the Pb composition and position shift of M5 site from the cell-twining plane. Band structure calculations confirmed that the structure is more stable when the position of M5 site is shifted away the cell-twining plane. Secondly, quaternary chalcogenides PbxSn6-xBi2Se9 (x=0 – 4) crystallizes in orthorhombic space group Cmcm (No. 62) and isostructural to the mineral heyrovskyite, Pb6Bi2S9. The PbxSn6-xBi2Se9 features a three-dimensional framework containing slabs of NaCl-(311) type with lillianite homologous series L(7, 7) . PbxSn6-xBi2Se9 exhibits identical layers of 7 octahedra wide slabs and each slab is composed of fused rectangular [M12Se12] rod units that are expanded along direction [010]. In the third section, quaternary selenides Sn2Pb5Bi4Se13 and Sn8.65Pb0.35Bi4Se15 were synthesized and crystallize in monoclinic space group C2/m (No.12). These compounds exhibit tropochemical cell-twinning of NaCl-type structures with lillianite homologous series L(4, 5) and L(4, 7) for Sn2Pb5Bi4Se13 and Sn8.65Pb0.35Bi4Se15, respectively. Measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps; Sn2Pb5Bi4Se13 is n-type, whereas Sn8.65Pb0.35Bi4Se15 is a p-type semiconductor with Seebeck coefficients -80(5) and 178(7) μV/K at 300K, respectively. Finally, quaternary chalcogenides Pb13Sb2.08Bi1.92Se19 was synthesized and crystallize in monoclinic space group C2/m (No.12), with lattice parameters of Pb13Sb2.08Bi1.92Se19: a = 14.127(3) Å, b =4.2625(8) Å, c = 34.477(6) Å, β= 96.329(4)°, R1/wR2 = 0.0351/0.0822 and GOF = 1.045. These structures reveal novel structure type. Pb13Sb2.08Bi1.92Se19 features a three-dimensional framework containing alternate layers of 7 and 8 octahedra wide slabs of NaCl-(311) type with lillianite homologous series L(7, 8). The semiconductor properties are confirmed with electronic calculations, Seebeck coefficient and electrical conductivity measurements.