Structures and physical properties of layered oxyselenides Ba(2)MO(2)Ag(2)Se(2) (M = Co, Mn).
Structures and physical properties of layered oxyselenides Ba(2)MO(2)Ag(2)Se(2) (M = Co, Mn).
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DOI：
10.1021/ic500203k
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发表时间：
2014-04
影响因子：
4.6
通讯作者：
Tingting Zhou;Yumei Wang;Shifeng Jin;Dandan Li;X. Lai;T. Ying;Han Zhang;S. Shen;Wenjun Wang;Xiaolong Chen
中科院分区：
文献类型：
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作者：
Tingting Zhou;Yumei Wang;Shifeng Jin;Dandan Li;X. Lai;T. Ying;Han Zhang;S. Shen;Wenjun Wang;Xiaolong Chen
通过固相反应成功合成了两种新型层状氧硒化物Ba2MO2Ag2Se2 (M = Co, Mn)。研究发现，这两种化合物由无限大的MO2方形平面和由钡分隔的反萤石型Ag2Se2层组成，在保持I4/mmm对称性的同时具有新的结构特征。对两种化合物和 Ba2ZnO2Ag2Se2 中氧与过渡金属的离散配位的详细计算揭示了截然不同的能量景观。计算结果表明，锰化合物有利于采用 I4/mmm 空间群，而钴化合物可能位于 I4/mmm 和 Cmca 相之间的过渡边界。在 Ba2CoO2Ag2Se2 中，大的钡离子和 Ag2Se2 层的共存显着扩展了氧化物层，并导致有史以来报道的方形平面片材中最大的 Co-O 键长。 Ba2CoO2Ag2Se2 接近化学计量，而 Ba2MnO2Ag2Se2 含有 7% 的银空位，这是通过 2+ 和 3+ 之间锰离子的混合价来解释的。在 Ba2CoO2Ag2Se2 中，零场冷却和场冷却磁化率在 159 K 处分叉，位于两个反铁磁 (AFM) 跃迁之间。同时，Ba2MnO2Ag2Se2 表现出高温居里-韦斯行为，随后发生 TN = 32 K 的低温 AFM 转变。它们都表现出半导体行为，室温下电阻率约为 10(5)Ω cm。 Ba2CoO2Ag2Se2 和 Ba2MnO2Ag2Se2 的光学带隙分别确定为 1.49 和 1.18 eV。能带结构计算表明Ba2CoO2Ag2Se2是一种直接能隙半导体，计算出的带隙为1.147 eV；然而，Ba2MnO2Ag2Se2 未能在 A 型 AFM 模型中再现半导体行为。
Two new layered oxyselenides, Ba2MO2Ag2Se2 (M = Co, Mn), have been successfully synthesized via solid-state reaction. It is found that these two compounds, consisting of the infinite MO2 square planes and antifluorite-type Ag2Se2 layers separated by barium, possess new structural features while keeping I4/mmm symmetry. A detailed calculation on the discrete coordination of transition metals by oxygen in the two compounds and Ba2ZnO2Ag2Se2 revealed quite different energy landscapes. The calculated results indicate that the manganese compound favors adoption of the I4/mmm space group, while the cobalt compound could be at the boundary of the transition between the I4/mmm and Cmca phases. In Ba2CoO2Ag2Se2, the coexistence of a large barium ion and a Ag2Se2 layer expands the oxide layer significantly and results in the largest Co-O bond length in the square-planar sheet ever reported. Ba2CoO2Ag2Se2 is near-stoichiometric, whereas Ba2MnO2Ag2Se2 contains 7% silver vacancies, which is explained by the mixed valence of the manganese ion between 2+ and 3+. In Ba2CoO2Ag2Se2, the zero-field-cooled and field-cooled susceptibilities bifurcate at 159 K, located between two antiferromagnetic (AFM) transitions. Meanwhile, Ba2MnO2Ag2Se2 shows high-temperature Curie-Weiss behavior, followed by a low-temperature AFM transition with TN = 32 K. They both exhibit semiconducting behavior with resisitivities of about 10(5)Ω cm at room temperature. The optical band gaps are determined to be 1.49 and 1.18 eV for Ba2CoO2Ag2Se2 and Ba2MnO2Ag2Se2, respectively. Band structure calculations reveal that Ba2CoO2Ag2Se2 is a direct-gap semiconductor, with a calculated band gap of 1.147 eV; however, Ba2MnO2Ag2Se2 failed to reproduce the semiconducting behavior within an A-type AFM model.