Acta Crystallographica Section B

Structural Science

Volume 52, Part 5 (October 1996)

research papers

Acta Cryst. (1996). B52, 780-789 [ doi:10.1107/S0108768196006519 ]

Incommensurate modulated disorder in Ba_0.85Ca_2.15In₆O₁₂

G. Baldinozzi, F. Goutenoire, M. Hervieu, E. Suard and D. Grebille

Abstract: 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( ${{1}\over{3}} {{1}\over{3}}$ [gamma] )]. 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.