Oxygen nonstoichiometry and actual Co valence in Na xCoO 2-δ

Maarit Karppinen; Isao Asako; Teruki Motohashi; Hisao Yamauchi

doi:10.1103/PhysRevB.71.092105

Oxygen nonstoichiometry and actual Co valence in Na _xCoO _2-δ

Maarit Karppinen^*, Isao Asako, Teruki Motohashi, Hisao Yamauchi

^*Tämän työn vastaava kirjoittaja

Tokyo Institute of Technology

Tutkimustuotos: Lehtiartikkeli › Article › Scientific › vertaisarvioitu

40 Sitaatiot (Scopus)

Abstrakti

The Na _xCoO _2-δ system - a host lattice for superb thermoelectrics and parent of the watery CoO ₂-layer superconductor - is found to be oxygen nonstoichiometric for x≤0.7, such that with decreasing x, the concentration of oxygen vacancies increases. Accordingly, upon Na deintercalation, the Co valence first increases but does not exceed the value of 3.5. To reveal this, the actual valence of Co was systematically determined by means of wet-chemical redox analysis for a series of Na _xCoO _2-δ samples with the Na content x ranging from 0.78 down to 0.12. The low-Na-content samples were obtained from Na-rich ones (0.70≤x≤0.78) through chimie douce extraction of Na utilizing I ₂, Br ₂, or NO ₂BF ₄ as an oxidizing agent. For the lowest-Na-content sample of x=0.12, the oxygen nonstoichiometry parameter δ was 0.23. The δ-x relation presently established for a wide x range of Na _xCoO _2-δ is indispensable for proper interpretations of physical properties of this system.

Alkuperäiskieli	Englanti
Artikkeli	092105
Julkaisu	Physical Review B - Condensed Matter and Materials Physics
Vuosikerta	71
Numero	9
DOI - pysyväislinkit	https://doi.org/10.1103/PhysRevB.71.092105
Tila	Julkaistu - 1 maalisk. 2005
OKM-julkaisutyyppi	A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä

Pääsy asiakirjaan

10.1103/PhysRevB.71.092105

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Siteeraa tätä

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title = "Oxygen nonstoichiometry and actual Co valence in Na xCoO 2-δ",

abstract = "The Na xCoO 2-δ system - a host lattice for superb thermoelectrics and parent of the watery CoO 2-layer superconductor - is found to be oxygen nonstoichiometric for x≤0.7, such that with decreasing x, the concentration of oxygen vacancies increases. Accordingly, upon Na deintercalation, the Co valence first increases but does not exceed the value of 3.5. To reveal this, the actual valence of Co was systematically determined by means of wet-chemical redox analysis for a series of Na xCoO 2-δ samples with the Na content x ranging from 0.78 down to 0.12. The low-Na-content samples were obtained from Na-rich ones (0.70≤x≤0.78) through chimie douce extraction of Na utilizing I 2, Br 2, or NO 2BF 4 as an oxidizing agent. For the lowest-Na-content sample of x=0.12, the oxygen nonstoichiometry parameter δ was 0.23. The δ-x relation presently established for a wide x range of Na xCoO 2-δ is indispensable for proper interpretations of physical properties of this system.",

author = "Maarit Karppinen and Isao Asako and Teruki Motohashi and Hisao Yamauchi",

year = "2005",

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doi = "10.1103/PhysRevB.71.092105",

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T1 - Oxygen nonstoichiometry and actual Co valence in Na xCoO 2-δ

AU - Karppinen, Maarit

AU - Asako, Isao

AU - Motohashi, Teruki

AU - Yamauchi, Hisao

PY - 2005/3/1

Y1 - 2005/3/1

N2 - The Na xCoO 2-δ system - a host lattice for superb thermoelectrics and parent of the watery CoO 2-layer superconductor - is found to be oxygen nonstoichiometric for x≤0.7, such that with decreasing x, the concentration of oxygen vacancies increases. Accordingly, upon Na deintercalation, the Co valence first increases but does not exceed the value of 3.5. To reveal this, the actual valence of Co was systematically determined by means of wet-chemical redox analysis for a series of Na xCoO 2-δ samples with the Na content x ranging from 0.78 down to 0.12. The low-Na-content samples were obtained from Na-rich ones (0.70≤x≤0.78) through chimie douce extraction of Na utilizing I 2, Br 2, or NO 2BF 4 as an oxidizing agent. For the lowest-Na-content sample of x=0.12, the oxygen nonstoichiometry parameter δ was 0.23. The δ-x relation presently established for a wide x range of Na xCoO 2-δ is indispensable for proper interpretations of physical properties of this system.

AB - The Na xCoO 2-δ system - a host lattice for superb thermoelectrics and parent of the watery CoO 2-layer superconductor - is found to be oxygen nonstoichiometric for x≤0.7, such that with decreasing x, the concentration of oxygen vacancies increases. Accordingly, upon Na deintercalation, the Co valence first increases but does not exceed the value of 3.5. To reveal this, the actual valence of Co was systematically determined by means of wet-chemical redox analysis for a series of Na xCoO 2-δ samples with the Na content x ranging from 0.78 down to 0.12. The low-Na-content samples were obtained from Na-rich ones (0.70≤x≤0.78) through chimie douce extraction of Na utilizing I 2, Br 2, or NO 2BF 4 as an oxidizing agent. For the lowest-Na-content sample of x=0.12, the oxygen nonstoichiometry parameter δ was 0.23. The δ-x relation presently established for a wide x range of Na xCoO 2-δ is indispensable for proper interpretations of physical properties of this system.

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