Stacking disorder in a layered carbonate phase: the structure of LaKOCO3

The structure of LaKOCO3 prepared by using the molten salt synthesis was ex amined by neutron diffraction, X-ray diffraction and electron diffraction. LnKOCO(3) has a layered structure strongly related to the T* structure know n from transition metal oxides, whereby the transition metal/oxygen layers of the latter are completely substituted by carbonate layers. Unlike in oth er layered carbonate phases, the carbonate ions are ordered and immobile in terms of rotation at 300 K. While the long-range orientation order within the layers is well established, a statistical orientation of the layer unit s was found around the axis perpendicular to the layers. The consequences o f this stacking disorder for the diffraction data were discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.