| Summary: | 碩士 === 國立交通大學 === 應用化學系分子科學碩博士班 === 100 === New quaternary selenides in TM1/TM2/Pn/Se (TM1, TM2 = transition metal; Pn = main group element) system was synthesized. All products were characterized by powder X-ray diffraction and these structures were determined by single crystal X-ray diffraction. The relationships between physical properties and electronic structures were also investigated. Two quaternary transition metal selenides, Ag0.46Mn1.08Pn2.46Se5 (Pn = Sb, Bi) were synthesized by solid state method at 923K. Both structures crystallize in the monoclinic system (Ag0.46Mn1.08Bi2.46Se5: space group C2/m, a = 13.418(3) Å, b = 4.0973(8) Å, c = 16.987(3) Å, β = 93.369(3)o, Z = 4; Ag0.46Mn1.08Sb2.46Se5: space group C2/m, a = 13.290(4) Å, b = 4.030(1) Å, c = 16.866(4) Å, β = 94.428(3) o, Z = 4). These compounds are isostructual with the AgBi3S5 that contains two types of layered slabs classified as the Pavonite homologous series P (5,1). The magnetic property of Ag0.46Mn1.08Bi2.46Se5 is Cuire-Weiss paramagnet at high temperature and undergoes antiferromagnetic ordering at low temperature. The Ag0.46Mn1.08Sb2.46Se5 well shows ferromagnetic behavior. The increase of electrical conductivity with increasing temperature indicates both compounds are semiconductors. The optical band gaps are 0.66 and 0.85 eV for Ag0.46Mn1.08Bi2.46Se5 and Ag0.46Mn1.08Sb2.46Se5, respectively. Measurements of Seebeck coefficient indicate n-type for Ag0.46Mn1.08Bi2.46Se5 (-745 μV/K. at 568 K) and p-type semiconductor for Ag0.46Mn1.08Sb2.46Se5 (249 μV/K at 608 K). These experimental results are corroborated by electronic band structure calculations.
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