Transmission Electron Microscopy Evidence of Spontaneous B-Cation Layered Distribution in NaNb1−xTaxO3

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• 作者：Almudena Torres-Pardo ; Frank Krumeich ; Jos M. Gonzlez-Calbet ; Ester Garca-Gonzlez
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：July 21, 2010
• 年：2010
• 卷：132
• 期：28
• 页码：9843-9849
• 全文大小：502K
• 年卷期：v.132,no.28(July 21, 2010)
• ISSN：1520-5126

文摘

A transmission electron microscopy (TEM) study of the complex NaNb_1−xTa_xO₃ (0.4 ≤ x ≤ 0.6) perovskites, combining high-resolution TEM and high-angle annular dark-field scanning TEM, has revealed the formation of extended areas on the crystals where niobium and tantalum order into layers in a 1:1 ratio. NaNb_1−xTa_xO₃ oxides are stoichiometric, and there is neither charge difference nor significant ionic size discrepancy between Nb(V) and Ta(V) cations. As d⁰ octahedrally coordinated cations, they show a propensity to second-order Jahn−Teller distortion. This distortion, however, manifests itself to different extents for the two cations and is considered the driving force for the layered ordered distribution observed. The niobium−tantalum segregation we have found can also be interpreted as a naturally occurring nanometer-scale phase separation. Albeit occurring in wide regions of the crystals and not in the entire grains, it shows a clear trend toward a long-range ordered disposition. This is reminiscent of the more general behavior of a recently documented class of perovskites that suffer spontaneous nanoscale phase separation to form a superlattice.