Browsing by Author "Chung, Ming-Yan"

Now showing 1 - 5 of 5

Ba3TM2Se9 (TM = Nb, Ta): Synthesis and Characterization of New Polyselenides
(2014-01-06)
Chung, Ming-Yan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
New ternary polyselenides Ba3TM2Se9 (TM = Nb, Ta) were synthesized through a solid-state reaction, and their structures were characterized using single-crystal X-ray diffraction. These compounds crystallized into a new structural type with a monoclinic space group P2(1)/c. The structures were constructed from distorted, close-packed layers of (3)(infinity)[BaSe3](3.33-) that incorporated TM atoms at octahedral sites and contained [(TM5+)(2)(Se2-)(7)(Se-2(2-))] units. Diffuse reflectance spectra and electronic resistivity measurements indicated semiconducting properties and optical band gaps of 1.3 eV for Ba3Nb2Se9 and 1.6 eV for Ba3Ta2Se9. Raman spectra were used to investigate the interatomic interactions. Calculations of the electronic structure verified the semiconducting behavior and bonding interaction of short Se-Se contacts.
Multinary Selenides with Unusual Coordination Environment of Bismuth
(2012-12-17)
Chung, Ming-Yan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
New multinary selenides Ae(3)SnPn(2)Se(8) (Ae = Sr, Ba; Pn = Sb, Bi), Sr8.01Ge2.04Bi7.95Se24, and Sr8YGe2Bi7Se24 were synthesized by solid-state reaction, and their structures were determined by single-crystal X-ray diffraction. These compounds crystallize in orthorhombic space group Pnma (no. 62) for Ae(3)SnPn(2)Se(8) (Ae = Sr, Ba; Pn = Sb, Bi) and in Pna2(1) (no. 33) for Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24. The structures feature one-dimensional corner sharing tetrahedral (1)(infinity)[MSe3] units, and one-dimensional edge sharing octahedral (1)(infinity)[M4Se10], 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)(infinity)[MSe3] chain. Diffuse reflectance spectra and electronic resistivity measurements indicate semiconducting behaviors; the Sr8YGe2Bi7Se24 Seebeck coefficient is -180 mu V/K at 303 K Electronic structure calculations confirm that the electron count for Sr8YGe2Bi7Se24 is optimal for interatomic bonding in the ionic network.
New quinternary selenides: Syntheses, characterizations, and electronic structure calculations
(2013-06-01)
Chung, Ming-Yan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Five quintemary selenides, Sr2.63Y0.37Ge0.63Sb2.32Se8 (I), Sr2.6La0.37Ge0.63Sb2.37Se8 (II) Sr2.71La0.29Sn0.77- Bi2.23Se8 (III), Ba2.67La0.33Sn0.67Sb2.33Se8 (IV), and Ba2.67La0.33Sn0.67Bi2.33Se8 (V), were synthesized by solid-state reaction in fused silica tubes. These compounds are isostructural and crystallize in the Sr3GeSb2Se8 structural-type, which belongs to the orthorhombic space group Pnma (no. 62). Three structural units, (1)(infinity)[MSe3], (1)(infinity)[M4Se10] (M=Tt, Pn) and M' (M'=groups II and III element), comprise the entire one-dimensional structure, separated by M'. Measurements of electronic resistivity and diffused reflectance suggest that IV and V have semiconducting properties. Electronic structure calculations confirm the site preferences of Sr/La element discovered by crystal structure refinement. (C) 2013 Elsevier Inc. All rights reserved.
Syntheses, Crystal Structures, Resistivities and Electronic Structures of Hf5Al3-xSbx (x=0.70, 1.44, 2.14)
(2013-07-01)
Huang, Wen-Heng
;
Chung, Ming-Yan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Three new hafnium aluminum antimonides Hf5Al3-xSbx (x = 0.70, 1.44, 2.14) were synthesized from pure elements in an arc-melting reaction; structures were solved from the X-ray diffraction data of single crystals. Al and Sb mixing produced two homogeneity ranges; the Mn5Si3 structural type was homogeneous for 0 x 1.0, and the W5Si3 structure covered the range 2.0 x 2.5. Both structures are condensations of two polyhedrons stacked along the c-axis. Calculations of the electronic structures revealed substantial contributions from Hf-Sb interactions; heteroatomic bonding in Hf-Al and Hf-Sb contacts affected the stabilities of these two phases. Measurements of the resistivity of polycrystalline samples revealed a dependence on temperature, indicating metallic behavior, consistent with the results of our calculations.
Synthesis and characterization of new quaternary polyselenide Ba4TMSbSe12 (TM = Nb, Ta)
(2019-09-01)
Chung, Ming-Yan
;
Chen, Guan-Ruei
;
Lee, Chi-Shen
;
交大名義發表
;
應用化學系
Two new quaternary polyselenides, Ba4TMSbSe12 (TM = Nb, Ta), are synthesized using a solid state reaction. They crystallize in a new structural type with a P-1 triclinic space group, characterized according to single-crystal X-ray diffraction. The structure is alternately stacked using isolated NbSe95- and SbSe33-, which are separated by Ba2+. The structure contains the NbSe95- unit with a bipentagonal pyramidal shape coordinated with Se2- and Se-2(2-) in monodenteate and bidentate modes. The vibrational property of the diselenide Se-2(2-) unit was studied using Raman spectrum analysis. ultraviolet-visible diffused reflectance and temperature-dependent resistivity measurements indicate semiconductor behaviors. Calculations of electronic structures indicate the presence of a band gap and strong Se-Se interactions in the diselenide group, which experimentally supports the measured physical properties.