Incommensurate modulated disorder in Ba_0.85Ca_2.15In₆O₁₂

The tunnel structure of the oxide Ba_0.85Ca_2.15In₆O₁₂ has been revisited. A mono-incommensurate modulation has been evidenced by electron diffraction. The simultaneous refinement of X-ray and neutron powder diffraction patterns has allowed a complete determination of the incommensurate structure [P3(γ)]. The existence of a modulated disorder, affecting Ba and Ca atoms, has been pointed out. The occupancy modulation concerning Ba and Ca atoms located on the hexagonal tunnel axis induces a modulation of the Ba—O bond lengths. The high-resolution electron microscopy study has shown the existence of twinning domains and of crystal regions possessing a defective arrangement of the modulation.

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