新穎多元鹼土硒化物的合成、鑑定與物性分析

Abstract

此篇博士論文包含多元含鹼土族金屬硒化物的合成、結構鑑定、物理性質、電子結構的討論。第一個部分關於多元系統Ae3SnPn2Se8，Ae2.66M0.33Tt0.67Pn2.33Se8 (Ae = Sr, Ba; M = Y, La;Tt = Ge, Sn; Pn = Sb, Bi)，Sr8.01Ge2.04Bi7.95Se24，與Sr8YGe2Bi7Se24。這些化合物呈現正交晶系，分別以Pnma (no. 62) 空間群(Ae3SnPn2Se8、Ae2.66M0.33Tt0.67Pn2.33Se8); Pna21 (no. 33) 空間群 (Sr8.01Ge2.04Bi7.95Se24、Sr8YGe2Bi7Se24)描述。一維的共角四面體((_"∞" ^"1" )"[M" 〖"Se" 〗_"3" "]" )與共邊四方三角錐((_"∞" ^"1" )"[" "M" _"4" 〖"Se" 〗_"10" "]" )，構成主要結構，其中鹼土、稀土族金屬包圍著一維結構單元。Sr8.01Ge2.04Bi7.95Se24與Sr8YGe2Bi7Se24呈現三倍的超晶格，主要是來自於在一維四面體中心，鉍與鍺的規則排列。漫反射光譜以及變溫電阻率量測顯示這些化合物為半導體。Seebeck係數量測指出Sr8YGe2Bi7Se24為n型半導體，並在室溫有-180 μV/K的係數。電子結構計算顯示Sr8YGe2Bi7Se24擁有最佳化的原子間作用力，也證實在單晶繞射精修所觀察到鍶與鑭的偏好位置。第二部分為新穎三元多硒化物Ba3TM2Se9 (TM = Nb, Ta)。此兩化合物是以新穎結構存在，呈現單斜晶系(空間群P21/c)。整體結構由鋇與硒以一比三的比例((_"∞" ^"3" )〖"[" 〖"BaSe" 〗_"3" "]" 〗^"-10/3" )構成扭曲的最密堆積，鈮或鉭插入其八面體空位，形成[TM2(Se2-)7(Se22-)]6+的單元。漫反射光譜以及變溫電阻率量測顯示此兩化合物皆為半導體，並分別具有1.3及1.6電子伏特之光學能隙。拉曼光譜用以研究化合物中多硒單元的原子間作用力。電子結構計算確認其半導體性質、多硒單元間的鍵結。第三部分關於兩個四元多硒化合物Ba4TMSbSe12 (TM = Nb, Ta)。它們呈現三斜晶系(P"1" ̅空間群)，並且是一個新穎結構化合物。整體結構由獨立單元NbSe95-與SbSe33-交互堆疊而成，單元間被鋇離子分隔。NbSe95-單元是由雙五角錐構成，中心Nb是被Se2-以及雙牙基Se22-多硒單元配位。拉曼光譜顯示其多硒單元的原子間作用力。紫外可見漫反射光譜與變溫電阻率量測顯示其半導體特質。電子結構計算顯示半導體特性，且具有直接能隙；在多硒單元內，顯示出Se-Se之間的作用力。第四部分為四元重金屬硒化物SrxPb4-xBi4Se10 (x = 1.08, 1.62)。整體結構與Pb4Sb4Se10相同。純相可以在x = 1.08獲得，此材料被鑑定為一半導體。室溫電阻率與Seebeck係數分別為 0.52 (歐姆厘米) 與 -150 (V/K)。第五部分，是在Ba-M'-Se (M' = Sn, Sb)系統發現的兩個多硒化物：Ba3Sb2Se7.17與Ba7Sn2Se14。此兩化合物皆是新穎結構，並且包含diselenide單元。Ba3Sb2Se7.17包含了兩種組成：Sb4Se14-12與Sb4Se15-12，鋇分散單元；基本單元是由蹺蹺板形SbSe4或是四角錐形SbSe5藉由角連接形成環狀四聚體。Ba7Sn2Se14是由四面體SnSe4以及二硒單元建構而成，單元間皆被鋇離子所分離。電子結構的計算，顯示出其半導體性質。第六部分仍是初步結果，兩個四元多硒化物Sr4.77Pb3.77Sb4.58Se17.5與Ba16Sb18.96Se42.34的合成，以及結構鑑定。

This dissertation discusses the systematic investigations of multinary selenides containing alkaline earth, and their structure, physical properties, and calculations of electronic structures are present. First, Ae3SnPn2Se8, Ae2.66M0.33Tt0.67Pn2.33Se8 (Ae = Sr, Ba; M = Y, La;Tt = Ge, Sn; Pn = Sb, Bi), Sr8.01Ge2.04Bi7.95Se24, and Sr8YGe2Bi7Se24were synthesized. These compounds crystallize in orthorhombic space group Pnma (no. 62) forAe3SnPn2Se8, Ae2.66M0.33Tt0.67Pn2.33Se8 (Ae = Sr, Ba; M = Y, La;Tt = Ge, Sn; Pn = Sb, Bi); and in Pna21 (no. 33) for Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24. The structures feature one-dimensional corner sharing tetrahedral(_"∞" ^"1" )"[M" 〖"Se" 〗_"3" "]" units, and one-dimensional edge sharing octahedral(_"∞" ^"1" )"[" "M" _"4" 〖"Se" 〗_"10" "]" , packed with the alkaline earth or rare earth cations. Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24 contain a triple cell superlattice structure derived from a special arrangement of Bi and Ge in the tetrahedrally coordinated (_"∞" ^"1" )"[M" 〖"Se" 〗_"3" "]" chain. Diffuse reflectance spectra and electronic resistivity measurements indicate semiconducting behaviors; the Sr8YGe2Bi7Se24 Seebeck coefficient is -180 μV/K at 303 K. Electronic structure calculations confirm that the electron count for Sr8YGe2Bi7Se24 is optimal for interatomic bonding in the ionic network, and site preferences of Sr/La elements discovered by crystal structure refinement. Second, new ternary polyselenides Ba3TM2Se9 (TM = Nb, Ta) were synthesized bya solid-state reaction. These compounds crystallize in a new structural type with monoclinic space group P21/c. The structures are constructed from distorted close-packed layers of (_"∞" ^"3" )〖"[" 〖"BaSe" 〗_"3" "]" 〗^"-10/3" that incorporate TM atoms at octahedral sites, and contain [TM2(Se2-)7(Se22-)]6- units. Diffuse reflectance spectra and electronic resistivity measurements indicate semiconducting properties and optical band gaps 1.3 eV for Ba3Nb2Se9 and 1.6 eV for Ba3Ta2Se9. Raman spectra served to investigate the interatomic interactions. Calculations of electronic structure confirmed the semiconducting behavior and bonding interaction of short Se-Se contacts. Third, two new quaternary polyselenides, Ba4TMSbSe12 (TM = Nb, Ta), are synthesized by solid state reaction. They crystallize in a new structure-type with a P"1" ̅ triclinic space group, characterized by single-crystal X-ray diffraction. The structure is alternatively stacked by isolated NbSe95- and SbSe33-, separated by Ba2+. The structure contains the NbSe95- unit with a bi-pentagonal pyramid shape coordinated with Se2- and Se22-anions in the mono and bidentate modes. The vibrational property of diselenide Se22- unit has been studied by Raman spectrum. UV-visible diffused reflectance and temperature dependence of resistivity indicatesthe semiconductor behavior. Calculations of the electronic structure indicate the presence of a band gap and strong Se-Se interactions in diselenide group, as experimentally confirmed.Fourth, two new heavy metal selenides in SrxPb4-xBi4Se10 (x = 1.08, 1.62) were synthesized and characterized. They crystallize in Pb4Sb4Se10 structure-type, with Pnma (No. 62) orthorhombic system. The pure phase of Sr1.085Pb2.915Bi4Se10 (x = 1.085) can be isolated, which behaves as a semiconductor. At room temperature, the resistivity and Seebeck coefficient is respectively 0.52 ( mm) and -150 (V/K). Fifth, two new polyselenides in Ba-M'-Q system (M' = Sn, Sb) were studied. Ba3Sb2Se7.17 and Ba7Sn2Se14 crystallized in new structure-types, in which short homonuclear Se-Se contacts are uncovered. Ba3Sb2Se7.17is comprised by two structural domains, Sb4Se14-12 and Sb4Se15-12, separated by Ba. To form the basic units, SbSe4 seesaws or SbSe5 square pyramids share corners and tetrmerize circularly. Ba7Sn2Se14 is build by the SnSe4 tetrahedra and Se22- diselenides, isolated by Ba. The calculations of electronic structure are indicative the semiconductor behaviors. Sixth, two polyselenides, Sr4.77Pb3.77Sb4.58Se17.5 and Ba16Sb18.96Se42.34, were investigated. Their structures are preliminary identified that belong to new structure-types.