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首页> 外文期刊>Crystal growth & design >Thin Film Synthesis and Structural Characterization of a New Kinetically Preferred Polymorph in the RE2Ti2O7 (RE = La-Y) Family
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Thin Film Synthesis and Structural Characterization of a New Kinetically Preferred Polymorph in the RE2Ti2O7 (RE = La-Y) Family

机译:RE2Ti2O7(RE = La-Y)家族中新的动力学上优选的多晶型物的薄膜合成和结构表征

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摘要

A new polymorph was found for all RE2Ti2O7 (RE = La-Y) compounds during their growth as epitaxial films on SrTiO3(110) substrates. Detailed structural characterization using X-ray and electron diffraction revealed that the new polymorph adopts an orthorhombic crystal structure with the space group Ammm and unit cell parameters (for La) of a = 7.89, b = 5.54, c = 13.45 angstrom; the refined lattice parameters decreased monotonically with decreasing size of the RE cation. Though these parameters are similar to those of the known monoclinic (110)-layered perovskite polymorph, the structures are not related by simple distortive transformations. While both of these polymorphs can be formed as epitaxial films on SrTiO3(110) substrates at T similar to 900 degrees C, the new polymorph is favored in conditions where diffusion is more limited between pulses. This implies that the new polymorph is kinetically favored during nucleation over the (110)-layered perovskite phase, in agreement with the smaller electroneutral unit of the new polymorph.
机译:发现所有RE2Ti2O7(RE = La-Y)化合物在SrTiO3(110)衬底上作为外延膜生长期间都有新的多晶型物。使用X射线和电子衍射进行的详细结构表征表明,新的多晶型物采用正交晶系晶体结构,空间群Ammm和单位晶胞参数(对于La)为a = 7.89,b = 5.54,c = 13.45埃;精制晶格参数随RE阳离子尺寸的减小而单调降低。尽管这些参数与已知的单斜晶(110)层钙钛矿多晶型物的参数相似,但这些结构并不通过简单的变形变换关联。虽然这两种多晶型物都可以在类似于900摄氏度的T下在SrTiO3(110)衬底上形成为外延膜,但在脉冲之间的扩散受到更多限制的条件下,这种新的多晶型物还是很受欢迎的。这意味着与(110)层钙钛矿相相比,新的多晶型物在成核过程中具有动力学上的优势,这与新的多晶型物的较小的电子中性单元相符。

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