Syntheses, Structures, Physical Properties, and Theoretical Studies of CeMxOS (M = Cu, Ag; x 0.8)

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• 作者：George H. Chan ; Bin Deng ; Mariana Bertoni ; John R. Ireland ; Mark C. Hersam ; Thomas O. Mason ; Richard P. Van Duyne ; James A. Ibers
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：October 2, 2006
• 年：2006
• 卷：45
• 期：20
• 页码：8264 - 8272
• 全文大小：245K
• 年卷期：v.45,no.20(October 2, 2006)
• ISSN：1520-510X

文摘

Black single crystals of the two nonstoichiometric cerium coinage-metal oxysulfide compounds CeCu_xOS andCeAg_xOS (x 0.8) have been prepared by the reactions of Ce₂S₃ and CuO or Ag₂O at 1223 or 1173 K, respectively.A black powder sample of CeAgOS has been prepared by the stoichiometric reaction of Ce₂S₃, CeO₂, Ag₂S, andAg at 1073 K. These isostructural materials crystallize in the ZrSiCuAs structure type with two formula units in thetetragonal space group P4/nmm. Refined crystal structure results and chemical analyses provide evidence that thepreviously known anomalously small unit-cell volume of LnCuOS for Ln = Ce (Ln = rare-earth metal) is the resultof Cu vacancies and the concomitant presence of both Ce³⁺ and Ce⁴⁺. Both CeCu_0.8OS and CeAgOS are paramagnetic with _eff values of 2.13(6) and 2.10(1) _B, respectively. CeCu_0.8OS is a p-type semiconductor with athermal activation energy E_a = 0.22 eV, _electrical = 9.8(1) 10^-3 S/cm at 298 K, and an optical band gap E_g < 0.73eV. CeAgOS has conductivity _conductivity = 0.16(4) S/cm and an optical band gap E_g = 0.71 eV at 298 K. Theoreticalcalculations with an on-site Coulomb repulsion parameter indicate that the Ce 4f states are fully spin-polarized andare not localized in CeCuOS, CeCu_0.75OS, or CeAgOS. Calculated band gaps for CeCu_0.75OS and CeAgOS are0.6 and 0.8 eV, respectively.