Incommensurate moderated disorder in Ba0.85Ca2.15In6O12

The tunnel structure of the oxide Ba0.85Ca2.15In6O12 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(1/3 1/3 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.