Structural investigation of oxygen non-stoichiometry and cation doping in misfit-layered thermoelectric (Ca{sub 2}CoO{sub 3-} {sub x} )(CoO{sub 2}) {sub {delta}} , {delta}{approx}1.61

Journal Article · Sun Apr 15 00:00:00 EDT 2007 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2007.02.016· OSTI ID:21015795

Aivazian, Karina ^[1]; Schmid, Siegbert ^[1]; Jensen, Paul ^[1]

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1. School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia)

The chemical and crystallographic natures of oxygen non-stoichiometry and cation doping in the 'misfit-layered' cobaltate [Ca{sub 2}CoO{sub 3-} {sub x} ][CoO{sub 2}] {sub {delta}} , {delta}{approx}1.61, were investigated. Single-phase polycrystalline samples were prepared with the help of a high-energy planetary ball mill, and single crystals grown from a K{sub 2}CO{sub 3}/KCl flux. Polycrystalline undoped, Ti{sup 4+}-doped, and Nd{sup 3+}-doped samples were annealed under both air and under argon in order to modify the oxygen non-stoichiometry. The incommensurately modulated composite crystal structures of undoped and Ti{sup 4+}-doped single crystals were refined against X-ray diffraction data using the superspace group X2/m(0,{delta},0)s0. For the as-made (air-annealed) undoped crystal, 14(2)% oxygen vacancies were found on the disordered O2 site in the central layer of the rock-salt-type subsystem, giving an overall stoichiometry [Ca{sub 2}CoO{sub 2.86}][CoO{sub 2}]{sub 1.61}. For the Ti{sup 4+}-doped crystal this site was found to be almost fully occupied, while Ti{sup 4+}-dopant cations were located on the disordered Co1 site in the central layer of the rock-salt-type subsystem, giving an overall formula [Ca{sub 2}Co{sub 0.74}Ti{sub 0.26}O{sub 2.98}][CoO{sub 2}]{sub 1.61}. In both cases, the average cobalt oxidation state is 3.13+. The single-crystal refinements, thermogravimetric analyses and variations in the lattice parameters of polycrystalline samples refined against synchrotron X-ray diffraction (XRD) data indicate that for both undoped and Ti{sup 4+}-doped samples, substantial numbers of additional oxygen vacancies (15-20%) can be introduced on this site by annealing under an inert atmosphere. Nd{sup 3+}-doped samples have a much lower tolerance (<5%) for oxygen vacancies. - Graphical abstract: The incommensurately modulated composite structure of [Ca{sub 2}CoO{sub 2.86}][CoO{sub 2}]{sub 1.61}.

• OSTI ID: 21015795
• Journal Information: Journal of Solid State Chemistry, Vol. 180, Issue 4; Other Information: DOI: 10.1016/j.jssc.2007.02.016; PII: S0022-4596(07)00090-4; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANNEALING
ARGON
CALCIUM OXIDES
COBALT OXIDES
CRYSTALLOGRAPHY
DOPED MATERIALS
INERT ATMOSPHERE
LATTICE PARAMETERS
MONOCRYSTALS
NEODYMIUM IONS
OXYGEN
POLYCRYSTALS
SALT DEPOSITS
STOICHIOMETRY
THERMAL GRAVIMETRIC ANALYSIS
TITANIUM IONS
VACANCIES
X-RAY DIFFRACTION