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首页> 外文期刊>Advanced Functional Materials >Nano- and Mesoscale Structure of Na_(1/2)Bi_(1/2)TiO_3: A TEM Perspective
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Nano- and Mesoscale Structure of Na_(1/2)Bi_(1/2)TiO_3: A TEM Perspective

机译：Na_（1/2）Bi_（1/2）TiO_3的纳米和中尺度结构：TEM的观点

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摘要

The room-temperature structure of Na_(1/2)Bi_(1/2)TiO_3 (NBT) ceramics was studied using several transmission electron microscopy (TEM) techniques. High-angle annular dark field imaging in a scanning TEM confirmed an essentially random distribution of Bi and Na, while electron diffraction revealed significant disorder of the octahedral rotations and cation displacements. Diffraction-contrast dark-field and Fourier-filtered high-resolution TEM images were used to develop a model that reconciles local and average octahedral tilting in NBT. According to this model, NBT consists of nanoscale twin domains which exhibit a~-a~-c~+ tilting. The coherence length of the in-phase tilting, however, is limited to a few unit cells and is at least one order of magnitude shorter than that of anti-phase tilting. Assemblages of such nanodomains are proposed to exhibit an average a~-a~-c~- tilt system. Diffuse sheets of intensity in electron diffraction patterns are attributed to local cation displacements correlated along both (111) and (100) chains and suggest partial polar ordering of these displacements. Overall, the TEM data indicate significant chemical, cation-displacement and tilt disorder of the NBT structure at the nano and mesoscale and support the premise that the Cc symmetry recently proposed from powder diffraction refinements is an averaged "best fit" cell.
机译：利用几种透射电子显微镜（TEM）技术研究了Na_（1/2）Bi_（1/2）TiO_3（NBT）陶瓷的室温结构。扫描TEM中的高角度环形暗场成像证实了Bi和Na基本上是随机分布的，而电子衍射显示出八面体旋转和阳离子位移的显着无序。衍射对比暗场和傅立叶滤波的高分辨率TEM图像用于开发一个模型，该模型可以协调NBT中的局部和平均八面体倾斜。根据该模型，NBT由表现出α〜-a〜-c〜+倾斜的纳米级双畴组成。然而，同相倾斜的相干长度限于几个单位单元，并且比反相倾斜的相干长度短至少一个数量级。提出这样的纳米域的组合物表现出平均的α-α-β-倾斜系统。电子衍射图中强度的扩散片归因于沿（111）和（100）链相关的局部阳离子位移，并表明这些位移的部分极性有序。总体而言，TEM数据表明NBT结构在纳米和中尺度上具有显着的化学，阳离子位移和倾斜紊乱，并支持这样一个前提，即最近从粉末衍射提纯中提出的Cc对称性是平均的“最佳拟合”单元。

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  • 来源
    《Advanced Functional Materials》 |2012年第16期|p.3445-3452|共8页
  • 作者

    Igor Levin; Ian M. Reaney;

  • 作者单位

    Ceramics Division National Institute of Standards and Technology Caithersburg MD 20899 USA;

    Department of Materials Science and Engineering University of Sheffield Sheffield, S13JD, UK;

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