| Summary: | 博士 === 國立成功大學 === 化學系 === 105 === We have discovered five new structures of chalcogenides in this reseach, which compounds are present in two parts according to their physical properties. Part one includes two new metal chalcoiodides were synthesized by solid-state reactions at 400 ºC. Crystal data: Bi2CuISe3 (1), monoclinic, C2/m, a = 14.243(2) Å, b = 4.1937(7) Å, c = 14.647(2) Å, = 116.095(2)°, V = 785.7(2) Å3, and Z = 4; Bi6Cu3S10I (2), orthorhombic, Pnma, a = 17.476(2) Å, b = 4.0078(4) Å, c = 27.391(2) Å, V = 1918.5(3) Å3, and Z = 4. Compound 1 adopts a three-dimensional structure formed by two alternative layers, which consist of BiSe5 square pyramids, BiSe4I2 octahedra, CuSe4 tetrahedra, and CuSe2I2 tetrahedra. Compound 2 possesses a new open framework made up of BiS5 square pyramides, BiS6 octahedra, BiS8 polyhedra, and CuS4 tetrahedra where I anions are encapsulated within the tunnels. Both electronic structures reveal that the hybridization of bismuth and chalcogenide orbitals dominates the bandgaps. The Cu d and I p states contribute to the top of valence bands in 1 and 2. The optical bandgaps determined by the diffuse reflectance spectra are 0.68 eV and 0.72 eV for 1 and 2, respectively. 1 is a p-type semiconductor with high Seebeck coefficients (S) of 460–575 V/K in the temperature range of 300–425 K. The electrical conductivity () is 0.02 S/cm and thermal conductivity is 0.22 W/mK at 425 K.
Part two includes three new metal chalcogenides identified in MnN–1(Gd2-xInx)SN+2 with N = 3, 4, and 5 via a KBr flux-growth synthesis. All compounds are crystallized in the same space group of orthorhombic Cmcm with cell constants: Mn2GdInS5 (3), a = 3.789(1) Å, b = 12.411(1) Å, c = 15.489(1) Å; Mn2Gd1.5In0.5S5 (3a), a = 3.790(1) Å, b = 12.462(2) Å, c = 15.612(2) Å; Mn3Gd2S6 (4), a = 3.778(1) Å, b = 12.505(2) Å, c = 19.114(2) Å; Mn4Gd2S7 (5), a = 3.769(1) Å, b = 12.466(2) Å, c = 22.289(3) Å. Compounds 3–5 form a homologus series through the modulation of MnS unit. These structures resprent a complete system of the corresponding lillianites (N1, N2L) of 3, 3L, 4,4L and 5, 5L. The gradually wider slabs formed in the series result in a monotonic increase along the c dimensions from 3 to 5. Crystal 5 is the first to achieve a predicted structure of 5, 5L. Mn2GdInS5 (3) displays a weak antiferromagnetic (AFM) ordering at 10 K and the Weiss constants () of 0.76 K. Mn2Gd1.5In0.5S5 (3a), an isostructure of 3, shifts the AFM transition tempeature to 12 K and possess a slightly larger constant of 6.06 K. Mn4Gd2S7 (5), featuring the thickest slabs in this series, shows a significant antiferromagnetic behavior beginning at high tempeature 70 K and has a largest constant of 40.25 K. A small amount of impurity -Gd2S3 with AFM transition temperature around 4 K was characterized in the sample 5, which do not interfere with the magnetic ordering of 5 at much higher temperature. These magnetic chalcogenides display band gaps of 1.66 eV for 3, 1.75 eV for 3a, and 1.44 eV for 5.
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