Nonstoichiometry and transport properties of Ca3 Co4±x O9+δ (x=0-0.4)

X. D. Zhou, L. R. Pederson, E. Thomsen, Z. Nie, G. Coffey

Research output: Contribution to journalArticle

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Abstract

Nonstoichiometries of Ca3 Co4 O9+δ and transport properties of Ca3 Co4±x O9+δ were investigated. At 1100°C, Ca3 Co4 O9+δ transformed to CaO and CoO. The reaction products offer a precise baseline for thermogravimetric analysis. At room temperature, δ in Ca3 Co4 O9+δ is 0.38, which decreases at T≈450°C, indicating the onset point of the formation of oxygen vacancies, and δ is ∼0.20 at 900°C. Correspondingly, the average Co valence state is 3.19 at room temperature and 3.10 at 900°C. In contrast to conventional defect chemistry theory in p-type oxide conductors, the formation of oxygen vacancies in Ca3 Co4 O9+δ has a negligible impact on the carrier density of holes, indicating that oxygen vacancies and the redox couple responsible for hole carriers are in different layers. With control over the ratio of CaCo, the phase boundary for the misfit layered structure is between Ca3 Co3.95 O9+δ and Ca3 Co4.05 O9+δ. Beyond the phase boundary, the second phase is present, which effectively lowers the electrical conductivity while increasing the Seebeck coefficient.

Original languageEnglish
JournalElectrochemical and Solid-State Letters
Volume12
Issue number2
DOIs
Publication statusPublished - 2009
Externally publishedYes

Fingerprint

Oxygen vacancies
Transport properties
transport properties
Phase boundaries
oxygen
Seebeck coefficient
room temperature
Seebeck effect
Reaction products
reaction products
Oxides
Carrier concentration
Thermogravimetric analysis
conductors
chemistry
valence
Temperature
Defects
electrical resistivity
oxides

ASJC Scopus subject areas

  • Electrochemistry
  • Electrical and Electronic Engineering
  • Materials Science(all)
  • Chemical Engineering(all)
  • Physical and Theoretical Chemistry

Cite this

Nonstoichiometry and transport properties of Ca3 Co4±x O9+δ (x=0-0.4). / Zhou, X. D.; Pederson, L. R.; Thomsen, E.; Nie, Z.; Coffey, G.

In: Electrochemical and Solid-State Letters, Vol. 12, No. 2, 2009.

Research output: Contribution to journalArticle

Zhou, X. D. ; Pederson, L. R. ; Thomsen, E. ; Nie, Z. ; Coffey, G. / Nonstoichiometry and transport properties of Ca3 Co4±x O9+δ (x=0-0.4). In: Electrochemical and Solid-State Letters. 2009 ; Vol. 12, No. 2.
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