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Title: 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

Abstract

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 samplesmore » 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}.« less

Authors:
 [1];  [2];  [2];  [2]
  1. School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia) and Bragg Institute, ANSTO, PMB 1, Menai, NSW 2234 (Australia), E-mail: c.ling@chem.usyd.edu.au
  2. School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia)
Publication Date:
OSTI Identifier:
21015795
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal 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)
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

Ling, Chris D., Aivazian, Karina, Schmid, Siegbert, and Jensen, Paul. 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. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.02.016.
Ling, Chris D., Aivazian, Karina, Schmid, Siegbert, & Jensen, Paul. 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. United States. doi:10.1016/j.jssc.2007.02.016.
Ling, Chris D., Aivazian, Karina, Schmid, Siegbert, and Jensen, Paul. Sun . "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". United States. doi:10.1016/j.jssc.2007.02.016.
@article{osti_21015795,
title = {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},
author = {Ling, Chris D. and Aivazian, Karina and Schmid, Siegbert and Jensen, Paul},
abstractNote = {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}.},
doi = {10.1016/j.jssc.2007.02.016},
journal = {Journal of Solid State Chemistry},
number = 4,
volume = 180,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie-Weiss behavior. Itmore » is concluded that with increasing x in [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca{sub 1.7}O{sub 2.1}H{sub 2.4}]{sub 0.58}[CoO{sub 2}]. -- Graphical abstract: In the misfit-layered [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] (0.0{<=}x{<=}0.2) system the x=0 phase has a commensurate match between the two layer blocks (i.e. q=0.5), while isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time Seebeck coefficient gets increased. Simultaneous increase in resistivity however outweighs this benefit, and accordingly the thermoelectric power factor is decreased. Display Omitted« less
  • Cited by 25
  • 3d metal K-shell X-ray absorption spectra of perovskites with the composition La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t{sub 2g}{sup Low-Asterisk} and a decrease in e{sub g}{sup Low-Asterisk} orbital occupancy, which ismore » most accentuated in the LaCoO{sub 3} sample. Virtually no Co K-edge shift was observed for the La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} compounds and the Co-O distances are also not significantly reduced when La{sup 3+} is partially substituted by Ca{sup 2+} or Sr{sup 2+}. From the pre-edge features of these perovskites we are tended to conclude that the t{sub 2g}{sup Low-Asterisk} orbitals are less, and the e{sub g}{sup Low-Asterisk} orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3{sup +} in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites in fact increase as much as x increases. - Graphical abstract: Co K and Fe K pre-edge of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites one of the evidences in favor of {delta}=x/2 for the Co-perovskites and {delta}=0 for the Fe-perovskites. Highlights: Black-Right-Pointing-Pointer XAS a valuable tool to evaluate the valence states of Co and Fe perovskites. Black-Right-Pointing-Pointer For La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} perovskites {delta} is close to x/2. Black-Right-Pointing-Pointer For La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} series {delta} is close to 0. Black-Right-Pointing-Pointer Discussion of the x dependency of the pre-edge bands.« less
  • A series of Ca{sub x}CoO{sub 2} (0.15{<=}x{<=}0.40) materials have been prepared by means of an ion exchange reaction from Na{sub x}CoO{sub 2}. Transmission electron microscopy (TEM) measurements revealed a rich variety of structural phenomena resulting from cation ordering, structural distortion, and twinning. Systematic structural analysis, in combination with the experimental data of Na{sub x}CoO{sub 2} (0.15{<=}x{<=}0.8) and Sr{sub x}CoO{sub 2} (1.5{<=}x{<=}0.4) systems, suggests that there are two common well-defined cation ordered states corresponding, respectively, to the orthorhombic superstructure at around x=1/2 and the 3{sup 1/2}ax3{sup 1/2}a superstructure at around x=1/3 in this kind of system. Multiple ordered states, phase separation,more » and incommensurate structural modulations commonly appear in the materials with 0.33<x<0.5. The TEM observations also reveal an additional periodic structural distortion with q{sub 2}=a{sup *}/2 in materials for x{<=}0.35. This structural modulation also appears in the remarkable superconducting phase Na{sub 0.33}CoO{sub 2}{center_dot}1.3H{sub 2}O.« less