Five-dimensional incommensurate structure of the melilite electrolyte [CaNd] 2 [Ga] 2 [Ga2O 7 ] 2
Date
2011
Authors
Wei, Fengxia
Baikie, Tom
An, Tao
Schreyer, Martin K
Kloc, Christian
White, Timothy
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American Chemical Society
Abstract
Melilite-type gallium oxides are potential intermediate temperature electrolytes for solid oxide fuel cells. Single crystals of [CaNd]2[Ga]2[Ga2O7]2 grown using an optical floating zone furnace have been investigated using transmission electron microscopy and powder and single-crystal X-ray diffraction. The anion array topologically conforms to a [(3.5.4.5)2, 3.5.3.5] network that contains distorted pentagonal tunnels. The distortion is necessary to achieve space filling and accommodate structural misfit between the layers. Satisfactory bond lengths and angles are obtained through two-dimensional modulation in the tetragonal based plane, leading to five-dimensional symmetry in the superspace group P4̄21m(α,α,0)00s(ᾱā,a,0)000, α = 0.2319(2), with modulation vectors q1 = α(a* + b*) and q2 = α(-a* + b*). Both displacive and occupational modulations are found. Through this mechanism, melilites are primed to accommodate mobile oxygen interstitials, suggesting a rational approach to crystallochemical tailoring that will enhance ionic diffusion and optimize electrolyte performance.
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Keywords: Bond lengths and angles; Gallium oxides; Incommensurate structure; Intermediate temperature electrolytes; Interstitials; Ionic diffusion; Melilite; Mobile oxygen; Modulation vectors; Optical floating zones; Single crystal x-ray diffraction; Space filling;
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Journal of the American Chemical Society
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Journal article
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2037-12-31
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