Structural considerations and high resolution electron microscopy observations on La[sub n]Ti[sub n[minus][sigma]]O[sub 3n] (n [ge] 4[sigma])

Crystals of the compounds La[sub n]Ti[sub n[minus][sigma]]O[sub 3n] are shown, by means of electron diffraction and high resolution electron microscopy, to form a homologous series of hexagonal or rhombohedral structures. The structures can be described as resulting from the perovskite structure by...

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Bibliographic Details
Published in:Journal of solid state chemistry 1994-02, Vol.108:2
Main Authors: Tendeloo, G.V., Amelinckx, S., Darriet, B., Bontchev, R., Darriet, J., Weill, F.
Format: Article
Language:English
Subjects:
360202 - Ceramics, Cermets, & Refractories- Structure & Phase Studies
CERAMICS
CHALCOGENIDES
CRYSTAL DEFECTS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
HEXAGONAL LATTICES
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
MATERIALS SCIENCE
OXIDES
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
STOICHIOMETRY
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRIGONAL LATTICES
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Summary:Crystals of the compounds La[sub n]Ti[sub n[minus][sigma]]O[sub 3n] are shown, by means of electron diffraction and high resolution electron microscopy, to form a homologous series of hexagonal or rhombohedral structures. The structures can be described as resulting from the perovskite structure by the periodic introduction of intrinsic stacking faults in a cubic stacking of close packed LaO[sub 3] layers. The titanium ions, which have mixed valencies, occupy the octahedral interstices in the fault planes remain vacant, making up for the nonstoichiometry. The corner-sharing TiO[sub 6] octahedra are found to be cooperatively tilted about the normal to the layer planes. The [open quotes]cut and projection[close quotes] method is used to analyze the electron diffraction patterns and to determine the stacking sequences from geometrical features of the diffraction patterns. Six different stacking sequences are confirmed by direct imaging. High resolution images support the tilt scheme of the TiO[sub 6] octahedra. The formation mechanism of the regular block sequences is discussed and the defects which allow this mechanism to operate are modeled and visualized.
ISSN:0022-4596
1095-726X
DOI:10.1006/jssc.1994.1048