新穎四元硒化物的合成、鑑定與物性分析

Abstract

在本論文中，我們使用固態燒結法合成四元硒化物，藉由單晶繞射解析其結構。並且研究這些化合物的電子結構與物理性質、結構特徵的相關性。 第一部分中，使用化學當量比例的元素在800° C真空狀態下合成四元硒化物InSn2Bi3Se8和In0.2Sn6Bi1.8Se9。InSn2Bi3Se8為C2/m (No. 12)空間群之單斜晶，晶胞常數為a = 13.557(3) Å、 b = 4.1299(8) Å、c = 15.252(3) Å、β= 115.73(3)°、 V = 769.3(3) Å3、 Z = 2。最後所得之R值為R1/ wR2/ GOF = 0.0206/0.0497/1.092。而In0.2Sn6Bi1.8Se9為Cmc21 (No. 36)空間群之斜方晶，晶胞常數為a = 4.1810(8) Å、 b = 13.799(3) Å、c = 31.953(6) Å、V = 1843.4(6) Å3、 Z = 4。R值為R1/ wR2/ GOF = 0.0966/0.2327/1.12。InSn2Bi3Se8和In0.2Sn6Bi1.8Se9分別與CuBi5S8和Bi2Pb6S9結構相同，並且都具有NaCl-(311)層狀結構，可分別分類為topochemical cell-twinning symbols L(3, 1)與L(7, 7)。電子結構計算、導電度與Seebeck量測結果顯示，此二化合物為狹窄能隙之n-型半導體，室溫下InSn2Bi3Se8和In0.2Sn6Bi1.8Se9的Seebeck係數分別為-270與-230 (μV/K)。 第二部分中，Ag2.40Ge3.67Sb6.78Se15為新結構化合物，屬於Cm (No. 8)空間群之單斜晶，晶胞常數為a = 13.456(3) Å、 b = 4.0707(8) Å、c = 26.309(5) Å、β= 104.78(3)°、 V = 1393.4(5) Å3、 Z = 2。最後所得之R值為R1/ wR2/ GOF = 0.0375/0.0868/1.063。Ag2.40Ge3.67Sb6.78Se15有NaCl-(311)層狀結構，為topochemical cell-twinning symbols L(10, 1)。固溶體Ag4.24-xGe2xSb8.62-xSe15具有的純相範圍在0.5 ≥ x ≥ 2.5內，並且在x等於5時具有晶相-非晶相相變化性質。晶相Ag4.24-xGe2xSb8.62-xSe15為半導體材料，其能隙隨Ge含量不同而在0.37 eV至0.47 eV內變動。 第三部分中，Pb4InxM6-xSe13 (M = Bi, x = 2.1-2.8; Sb, x = 2)與Pb4In2Bi4S13結構相同，屬於Pbam (No. 55)空間群之斜方晶。其結構包含Z字型緞帶狀單元與Corner-sharing [InSe4]∞的一維無限鏈狀單元，此二單元借由Pb原子連接形成三維立體結構。電子結構計算、導電度、反射式紫外-可見光(UV-vis)吸收光譜與Seebeck量測結果顯示，此化合物為狹窄能隙之n-型半導體，室溫下的Seebeck係數分別為-180 (μV/K)。 最後，合成之多元硒化物Sn18Sb12Se36, Sn4Bi10Se19, Sn4(In,Sb)14Se25, Sn8(In,Sb)18Se35, Sn10(In,Sb)18Se37, Sn10.25Bi17.75Se37, Sn8.22Pb1.74Bi18.04Se37可歸納為homologous series [M2xSe2x+2][M2y-2zSe3y-2z-1]，其參數x、 y與z 值受到結構上的限制，並且受到M2+/M3+離子比例的影響。此外，Sn8(In,Sb)34Se59具有與此homologous series相似特徵之結構亦在此作討論。

In this dissertation, all quaternary selenides were synthesized by solid state method. Their structures were determined with X-ray diffraction of single crystals. The relationship between the physical properties, crystal structural characters and electronic structures using LMTO calculation for these compounds were also investigated. Firstly, quaternary chalcogenides InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9 were synthesized on direct combination of their elements in stoichiometric ratios at T > 800° C under vacuum. InSn2Bi3Se8 crystallizes in monoclinic space group C2/m (No. 12) with a = 13.557(3) Å, b = 4.1299(8) Å, c = 15.252(3) Å, β= 115.73(3)°, V = 769.3(3) Å3, Z = 2, and R1/ wR2/ GOF = 0.0206/0.0497/1.092; In0.2Sn6Bi1.8Se9 crystallizes in orthorhombic space group Cmc21 (No. 36) with a = 4.1810(8) Å, b = 13.799(3) Å, c =31.953(6) Å, V = 1843.4(6) Å3, Z = 4, and R1/ wR2/ GOF = 0.0966/0.2327/1.12. InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9 are isostructural with CuBi5S8 and Bi2Pb6S9 phases, respectively, containing slabs of NaCl-(311) type with topochemical cell-twinning symbols L(3, 1) and L(7, 7). Calculations of the electronic structure and measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps. Both compounds show n-type semiconducting properties with Seebeck coefficients -270 and -230 μV/K at 300 K for InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9, respectively. Secondly, new quaternary chalcogenide Ag2.40Ge3.67Sb6.78Se15 crystallize with a new structure type, monoclinic space group Cm (No. 8) with a = 13.456(3) Å, b = 4.0707(8) Å, c = 26.309(5) Å, β= 104.78(3)°, V = 1393.4(5) Å3, and Z = 2. The final R values are R1 = 0.0375, wR2 = 0.0868 and GOF = 1.063. The structure of Ag2.40Ge3.67Sb6.78Se15 features three-dimensional framework consisting NaCl-(311) type slabs with topochemical cell-twinning symbols L(10, 1). The solid solutions Ag4.24-xGe2xSb8.62-xSe15 exhibited pure phase with x = 0.5-2.5 and exhibits phase-change properties with x = 2.5. The physical property measurements of crystalline Ag4.24-xGe2xSb8.62-xSe15 show semiconducting properties with a narrow band gap between 0.37 eV and 0.47 eV. In the third section, the selenides of Pb4InxM6-xSe13 (M = Bi, x = 2.1-2.8; Sb, x = 2) are isostructural with Pb4In2Bi4S13 and crystallize in the orthorhombic space group Pbam (No. 55) with Z = 4; the structure features a three-dimensional framework consisting of Z-shaped ribbon units and corner-sharing infinite one-dimensional [InSe4]∞ chains running parallel to the c-axis, which are connected by Pb atoms to form a three-dimensional structure. Calculations of the band structure and measurements of Seebeck coefficient, electrical conductivity and diffuse reflectance spectra confirm that these compounds are semiconductors with a narrow band gap. All compounds show semiconducting properties; the Seebeck coefficient of Pb4In2.5Bi3.5Se13 is -180 μV/K at 295 K. Finally, the new selenides Sn18Sb12Se36, Sn4Bi10Se19, Sn4(In,Sb)14Se25, Sn8(In,Sb)18Se35, Sn10(In,Sb)18Se37, Sn10.25Bi17.75Se37, Sn8.22Pb1.74Bi18.04Se37 are synthesized and all are members of a new homologous series, [M2xSe2x+2][M2y-2zSe3y-2z-1]. The structure contains NaCl100-type unit and NaCl111-type units, and the available value x, y, and z were constrained by structural feature and M2+/M3+ Ratio. One special case Sn8(In,Sb)34Se59 are also reported that exhibits similar structural feature to this series.