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• 作者：Shifeng Jin ; Xiaolong Chen ; Jiangang Guo ; Ming Lei ; Jingjing Lin ; Jianguo Xi ; Wenjun Wang ; Wanyan Wang
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：October 1, 2012
• 年：2012
• 卷：51
• 期：19
• 页码：10185-10192
• 全文大小：449K
• 年卷期：v.51,no.19(October 1, 2012)
• ISSN：1520-510X

文摘

Four new oxyselenides with nominal formula Sr₂AO₂M₂Se₂ (A=Co, Mn; M=Cu, Ag) have been synthesized. They all crystallize in an I4/mmm space group and consist of alternating perovskite-like (Sr₂AO₂)²⁺ blocks and antiflourie (M₂Se₂)^2- layers, which are relatively rare layered oxyselenides reported so far that are isostructural to Sr₂Mn₃Sb₂O₂. From powder X-ray diffraction data, compounds Sr₂CoO₂Cu₂Se₂ and Sr₂CoO₂Ag₂Se₂ are found near stoichiometric, whereas Sr₂MnO₂Cu_2-未Se₂ and Sr₂MnO₂Ag_2-未Se₂ possess substantial copper or silver vacancies (未鈮?.5), consistent with their oxysulfide analogues. X-ray photoelectron spectroscopy measurements indicate the readily oxidization of Mn²⁺ ions should be responsible for the occurrence of Cu/Ag vacancies. The rigid (Sr₂AO₂)²⁺ blocks within these compounds constrain the basal lattice parameters in the ab plane and result in largely deformed tetrahedral sites for the large silver ions. Magnetic susceptibility measurements of Sr₂CoO₂M₂Se₂ (M=Cu, Ag) show complex antiferromagnetic transitions, while Sr₂MnO₂M_2-未Se₂ (M=Cu, Ag) show high-temperature Curie鈥揥eiss behavior, followed by low-temperature antiferromagnetic transitions at 54 K and 67 K, respectively. Except for Sr₂MnO₂Ag_2-未Se₂, the other three compounds exhibit p-type semiconducting transport properties, with the measured resistivities several orders lower than their oxysulfide analogues. Hall measurement reveals high mobilities of Sr₂CoO₂M₂Se₂ (M=Cu, Ag) compounds at room temperature. The unusually small optical band gaps (0.07 eV) of Sr₂CoO₂Cu₂Se₂, Sr₂CoO₂Ag₂Se₂, and Sr₂MnO₂Cu_2-未Se₂ are also reported.