Distinguishing between the bi-stripe and Wigner-crystal model: A crystallographic study of charge-ordered La 0.33 Ca 0.67 MnO 3
Distinguishing between the bi-stripe and Wigner-crystal model: A crystallographic study of charge-ordered La 0.33 Ca 0.67 MnO 3
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DOI：
10.1103/physrevb.61.11946
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发表时间：
2000-05
影响因子：
3.7
通讯作者：
Renhui Wang;J. Gui;Yimei Zhu;A. Moodenbaugh
中科院分区：
文献类型：
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作者：
Renhui Wang;J. Gui;Yimei Zhu;A. Moodenbaugh
为了解决维格纳晶体和双条纹模型之间电荷有序结构的差异，利用定量电子衍射和高分辨率成像研究了 ${\mathrm{La}}_{0.33}{\mathrm{Ca}}_{0.67}{\mathrm{MnO}}_{3}$。基于动态电子衍射理论的图像模拟表明，${\mathrm{Mn}}^{3+}{\ensuremath{-}\mathrm{M}\mathrm{n}}^{3+}$ 和 ${\mathrm{Mn}}^{3+}{\ensuremath{-}\mathrm{M}\mathrm{n}}^{4+}$ 条纹之间的间距存在明显差异，即双条纹模型的基础，可能会随着成像条件的不同而显着变化，并且可能不能直接代表原子平面实际间距的差异。使用平行和会聚光束对远离缺陷的晶体区域进行电子衍射研究，揭示了与双条纹模型的大纵向位移不相容的$a[001]$滑移面和$n[100]$对角滑移面的存在。尽管我们的研究支持维格纳晶体模型，但详细分析表明，在我们的样本中，材料中的不相称电荷调制具有平均波矢 $\mathbf{q}=(0.284,0,\ensuremath{\xi})$ 和 $|\ensuremath{\xi}|=0.010。$ 与沿 c 轴的小分量 \ensuremath{\xi} 相关的对称性破缺尚未得到证实。先前通过高分辨率 X 射线或中子粉末衍射观察到。
In order to resolve discrepancies in the charge-ordered structure between the Wigner-crystal and bi-stripe models, ${\mathrm{La}}_{0.33}{\mathrm{Ca}}_{0.67}{\mathrm{MnO}}_{3}$ was studied using quantitative electron diffraction and high-resolution imaging. Image simulations based on dynamic electron-diffraction theory suggest that the apparent difference in spacing between the ${\mathrm{Mn}}^{3+}{\ensuremath{-}\mathrm{M}\mathrm{n}}^{3+}$ and ${\mathrm{Mn}}^{3+}{\ensuremath{-}\mathrm{M}\mathrm{n}}^{4+}$ stripes, which is the basis of the bi-stripe model, can vary significantly with imaging conditions and may not directly represent the difference in actual spacing of atomic planes. Electron-diffraction study of crystal regions far away from defects, using parallel and convergent beams, reveal the existence of $a[001]$ glide planes and $n[100]$ diagonal glide planes that are incompatible with the large longitudinal displacement of the bi-stripe model. Although our study supports the Wigner-crystal model, detailed analysis suggests that, in our samples, the incommensurate charge modulation in the material has an average wave vector $\mathbf{q}=(0.284,0,\ensuremath{\xi})$ with $|\ensuremath{\xi}|=0.010.$ The symmetry breaking associated with the small component \ensuremath{\xi} along the c axis has not been previously observed by high-resolution x-ray or neutron powder diffraction.