四元硒化合物MnAgBi3Se6、MnAgSb3Se6與Fe2Ag5Sb13Se24的合成、結構與物性分析

Abstract

本論文研究成功地以固態燒結法在1023K下合成出具有礦物Benjaminite結構之新四元硒化合物MnAgBi3Se6、MnAgSb3Se6與Fe2Ag5Sb13Se24。利用單晶繞射儀收集三種化合物的繞射點，解析得空間群為Cm。MnAgBi3Se6晶胞常數為a = 13.479(3) Å，b = 4.1007(8) Å，c = 21.150(4) Å，β = 104.10(3) ° (Z = 4)，R1/ wR2 = 0.0327/0.0621。MnAgSb3Se6晶胞常數為a = 13.395(3) Å，b = 4.0534(8) Å，c = 20.775(4) Å，β = 102.96(3) ° (Z = 4)，R1/ wR2 = 0.0384/0.0886。Fe2Ag5Sb13Se24晶胞常數為a = 13.490(3) Å，b = 4.0972(8) Å，c = 20.763(4) Å，β = 102.42(3) °(Z = 1)，R1/ wR2 = 0.0345/0.0866。MnAgBi3Se6在300K電阻率約為87.5 Ohm．cm；MnAgSb3Se6為130.7 Ohm．cm；Fe2Ag5Sb13Se24為1.2638×10-2 Ohm．cm，三種化合物的電阻率皆是隨溫度上升而下降的半導體行為。UV-VIS反射式吸收光譜得知半導體能距皆小於0.62eV。由Seebeck係數量測得知化合物Fe2Ag5Sb13Se24為P型半導體，在溫度320K時係數為398 μV/K。磁性量測顯示MnAgBi3Se6與MnAgSb3Se6為順磁性，Fe2Ag5Sb13Se24 在350K以下皆具鐵磁性。TB-LMTO法電子自旋極化(spin-polarized)理論計算顯示反鐵磁性的MnAgBi3Se6與MnAgSb3Se6、鐵磁性的Fe2Ag5Sb13Se24皆較非磁性(nonmagnetic)計算結果穩定。

Three new quaternary selenides MnAgBi3Se6, MnAgSb3Se6, and Fe2Ag5Sb13Se24 were prepared by directly reacting the elements in stoichiometric ratios at 1023K. Their structures have been determined by single-crystal X-ray diffraction. All phases are isostructural to the Benjaminite type. MnAgBi3Se6, MnAgSb3Se6 and Fe2Ag5Sb13Se24 crystallize in the monoclinic space group Cm with a = 13.479(3) Å, b = 4.1007(8) Å, c = 21.150(4) Å, β = 104.10(3)° (Z = 4), R1/ wR2 = 0.0327/0.0621 , a = 13.395(3) Å, b = 4.0534(8) Å, c = 20.775(4) Å, β = 102.96(3)° (Z = 4), R1/ wR2 = 0.0384/0.0886 and a = 13.490(3) Å, b = 4.0972(8) Å, c = 20.763(4) Å, β = 102.42(3)° (Z = 1)，R1/ wR2 = 0.0345/0.0866, respectively. The room temperature resistivity of MnAgBi3Se6, MnAgSb3Se6 and Fe2Ag5Sb13Se24 are 87.5, 130.7 and 1.2638×10-2 Ohm．cm, respectively. For all compounds, the resistivity decrease with increasing temperature, indicative of semiconducting behaviors. UV-Visible absorption measurements show that the band gaps of all phases are lower than 0.62 eV. Seebeck coefficient of Fe2Ag5Sb13Se24 is 398 μV/K at 320 K, exhibiting p-type semiconductor. Temperature dependence susceptibilities measurements indicate paramagnetic property for MnAgBi3Se6 and MnAgSb3Se6 and ferromagnetic property for Fe2Ag5Sb13Se24 blow 350K. Band structure calculations using TB-LMTO method show that the calculations with spin-polarized models are more stable than the nonmagnetic models.