Wei, FengxiaBaikie, TomAn, TaoSchreyer, Martin KKloc, ChristianWhite, Timothy2015-12-100002-7863http://hdl.handle.net/1885/56861Melilite-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.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;Five-dimensional incommensurate structure of the melilite electrolyte [CaNd] 2 [Ga] 2 [Ga2O 7 ] 2201110.1021/ja206441x2016-02-24