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首页> 外文期刊>Acta Crystallographica, Section B. Structural science, crystal engineering and materials >(Na,□)_5[MnO_2]_(13) nanorods: a new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data
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(Na,□)_5[MnO_2]_(13) nanorods: a new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data

机译：（Na，□）_5 [MnO_2] _（13）纳米棒：一种从头开始确定并通过电子和同步加速器衍射数据组合精制的电极材料的新型隧道结构

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摘要

(Na_(x□1 - x))_5[MnO_2]_(13) has been synthesized with x = 0.80 (4), corresponding to Na_(0.31)[MnO_2]. This well known material is usually cited as Na_(0.4)[MnO_2] and is believed to have a romanè chite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (x~2 = 0.690, R_(wp) = 0.051, R_p = 0.037, R_(F2) = 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) ? , β = 105.0925 (16)°, V = 918.90 (4) ?~3, Z = 2. A hitherto unknown [MnO_2] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by eggshaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)_5[MnO_2]_(13). The trivalent Mn~(3+) ions concentrate at two of the seven Mn sites where larger Mn-O distances and Jahn–Teller distortion are observed. One of the Mn~(3+) sites is five-coordinated in a square pyramid which, on oxidation to Mn~(4+), may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures.
机译：（Na_（x□1-x））_ 5 [MnO_2] _（13）已合成，其中x = 0.80（4），对应于Na_（0.31）[MnO_2]。这种众所周知的材料通常被引用为Na_（0.4）[MnO_2]，并被认为具有罗曼诺（romanè）香茅状的骨架。在这里，它的真实结构从头开始是通过单晶电子衍射断层扫描（EDT）确定的，并通过使用动态散射理论的EDT数据和基于同步加速器粉末衍射数据的Rietveld方法进行精制（x〜2 = 0.690，R_ （wp）= 0.051，R_p = 0.037，R_（F2）= 0.035）。晶胞是单斜C2 / m，a = 22.5199（6），b = 2.83987（6），c = 14.8815（4）？ ，β= 105.0925（16）°，V = 918.90（4）？〜3，Z =2。发现了迄今未知的[MnO_2]骨架，该骨架主要基于边角和边角共享八面体，包括三种类型的隧道：每个晶胞，两个由S形10环定义，四个由蛋形8环定义，两个由Mn多面体的略椭圆形6环定义。 Na占据所有隧道。如此确定的结构很好地解释了以前有关（Na，□）_5 [MnO_2] _（13）电化学的报道。三价Mn〜（3+）离子集中在七个Mn位置中的两个位置，其中观察到较大的Mn-O距离和Jahn-Teller畸变。 Mn〜（3+）位点之一在四角锥中是五配位的，在氧化成Mn〜（4+）时，很容易发生向正八面体的正离子转化，提示在不同隧道结构之间可能发生过渡。

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