High-resolution electron microscopic study of ba7sc6al2o19 and related phases

Abstract It is shown that the crystal structures of the compound Ba 7 Sc 6 Al 2 O 19 and of related structures which belong to the class of hexagonal perovskites can be interpreted as mixed-layer structures consisting of the intergrowth of structural blocks (or lamellae) of β-Ba 2 ScAlO 5 and Ba 3 Sc 4 O 9 , two other hexagonal perovskites. The block sequences have been imaged directly by means of high-resolution electron microscopy. The characteristic geometrical features of the structural blocks allow unambiguous identification of the different sequences. The image interpretation was confirmed by computer-simulated images. The structures can alternatively be considered as interface modulated structures derived from a cubic stacking of close-packed BaO 3 layers in which periodic stacking faults and twin boundaries are introduced. These interfaces are stabilized by B cations.