| Summary: | 博士 === 國立交通大學 === 應用化學系碩博士班 === 101 === 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.
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