TY - JOUR
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
Y1 - 2012/5/21
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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U2 - 10.1021/ic300585t
DO - 10.1021/ic300585t
M3 - Article
AN - SCOPUS:84861324110
SN - 0020-1669
VL - 51
SP - 5941
EP - 5949
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 10
ER -