Three Forms of the Misfit Layered Cobaltite [Ca2CoO3] [CoO2]1.62·A 4D Structural Investigation

✍ Scribed by Sébastien Lambert; Henri Leligny; Dominique Grebille

• Book ID: 102611185
• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 364 KB
• Volume: 160
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2001.9235

✦ Synopsis

Three mis5t layer compounds with the same chemical formula Ca 3 Co 4؊x O 9؉ were isolated in the Ca+Co+O system. They exhibit either a monoclinic or an orthorhombic symmetry. These crystals are constituted of two interpenetrating C sublattices showing incommensurate periods along the b axis. The structure of the three crystals can be described as an alternate stacking along [001] of distorted rock-salt-type slabs [Ca 2 CoO 3 ] and of [CoO 2 ] layers displaying a distorted CdI 2 -type structure. Relating to the symmetry and the di4erent observed c periods, di4erent sequences are found for the [CoO 2 ] layers running along [001] within the three crystals. Two of them were determined by single X-ray di4raction using the 4D superspace formalism. A signi5cant displacive modulation is implied, acting mainly on Ca and O atoms involved in the intersystem bonding scheme. This modulation leads to a noticeable distortion of the CoO 6 octahedra of the [CoO 2 ] layers. Strong interactions, via Ca+O bonds, are evidenced between the two sublattices. A systematic positional disorder is observed inside the [CoO] layer.