INCOMMENSURATE MODERATED DISORDER IN BA0.85CA2.15IN6O12

The tunnel structure of the oxide Ba0.85Ca2.15In6O12 has been revisite d. A mono-incommensurate modulation has been evidenced by electron dif fraction. The simultaneous refinement of X-ray and neutron powder diff raction patterns has allowed a complete determination of the incommens urate structure [P3(1/3 1/3 gamma)]. The existence of a modulated diso rder, affecting Ba and Ca atoms, has been pointed out. The occupancy m odulation concerning Ba and Ca atoms located on the hexagonal tunnel a xis 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 modu lation.