Crystal chemistry of melilite [CaLa] 2[Ga] 2[Ga 2O 7] 2: A five dimensional solid electrolyte

Fengxia Wei; Tom Baikie; Tao An; Christian Kloc; Jun Wei; Tim White

doi:10.1021/ic300585t

Crystal chemistry of melilite [CaLa] ₂[Ga] ₂[Ga ₂O ₇] ₂: A five dimensional solid electrolyte

Fengxia Wei^*, Tom Baikie, Tao An, Christian Kloc, Jun Wei, Tim White

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

16 Citations (Scopus)

Abstract

Melilite-type [A ₂] ₂[B ^I] ₂[B ^II ₂O ₇] ₂ gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa] ₂[Ga] ₂[Ga ₂O ₇] ₂, grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga ₂O ₇] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P4̄2 ₁m(α α, 0)00s(ᾱ, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) Å, c = 5.2641(3) A, onto which modulation vectors are superimposed: q ₁ = α (a* + b*), q ₂ = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.

Original language	English
Pages (from-to)	5941-5949
Number of pages	9
Journal	Inorganic Chemistry
Volume	51
Issue number	10
DOIs	https://doi.org/10.1021/ic300585t
Publication status	Published - 21 May 2012

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@article{767cba711fa54dd684e92a7b5ccd329d,

title = "Crystal chemistry of melilite [CaLa] 2[Ga] 2[Ga 2O 7] 2: A five dimensional solid electrolyte",

abstract = "Melilite-type [A 2] 2[B I] 2[B II 2O 7] 2 gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa] 2[Ga] 2[Ga 2O 7] 2, grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga 2O 7] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P{\=4}2 1m(α α, 0)00s(ᾱ, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) {\AA}, c = 5.2641(3) A, onto which modulation vectors are superimposed: q 1 = α (a* + b*), q 2 = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.",

author = "Fengxia Wei and Tom Baikie and Tao An and Christian Kloc and Jun Wei and Tim White",

year = "2012",

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T1 - Crystal chemistry of melilite [CaLa] 2[Ga] 2[Ga 2O 7] 2

T2 - A five dimensional solid electrolyte

AU - Wei, Fengxia

AU - Baikie, Tom

AU - An, Tao

AU - Kloc, Christian

AU - Wei, Jun

AU - White, Tim

PY - 2012/5/21

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N2 - Melilite-type [A 2] 2[B I] 2[B II 2O 7] 2 gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa] 2[Ga] 2[Ga 2O 7] 2, grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga 2O 7] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P4̄2 1m(α α, 0)00s(ᾱ, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) Å, c = 5.2641(3) A, onto which modulation vectors are superimposed: q 1 = α (a* + b*), q 2 = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.

AB - Melilite-type [A 2] 2[B I] 2[B II 2O 7] 2 gallates are promising ion conducting electrolytes for deployment in solid oxide fuel cells. Single crystals of [CaLa] 2[Ga] 2[Ga 2O 7] 2, grown in an optical floating zone furnace, were investigated using a combination of transmission electron microscopy and single crystal X-ray diffraction. Strong anisotropic displacements of oxygen arise from the structural misfit between the interlayer Ca/La cations and the [Ga]-[Ga 2O 7] tetrahedral layers. A model employing two-dimensional modulation achieves bond lengths and bond angles that preserve satisfactory bond valence sums throughout the structure. The melilite belongs to the tetragonal superspace group P4̄2 1m(α α, 0)00s(ᾱ, α, 0)000, α = 0.2160(5), with a subcell metric of a = 7.9383(2) Å, c = 5.2641(3) A, onto which modulation vectors are superimposed: q 1 = α (a* + b*), q 2 = α (-a* + b*). Both displacive (cation and anion) and occupational (cation) modulations contribute to incommensuration. The analysis of structural adjustments that accompany changes in temperature and composition provides assurance that the crystal chemical model is correct. By better understanding the flexibility of this modulated structure a rational approach toward crystallochemical optimization of electrolyte performance by enhancing oxygen mobility becomes feasible.

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Crystal chemistry of melilite [CaLa] ₂[Ga] ₂[Ga ₂O ₇] ₂: A five dimensional solid electrolyte

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