Comparative Study of Electrical Conduction and Oxygen Diffusion in the Rhombohedral and Bixbyite Ln 6 MoO 12 (Ln = Er, Tm, Yb) Polymorphs

Anna V. Shlyakhtina, Nikolay V. Lyskov, Maxim Avdeev, Vladimir G. Goffman, Nikolay V. Gorshkov, Alexander V. Knotko, Igor V. Kolbanev, Olga K. Karyagina, Konstantin I. Maslakov, Lidia G. Shcherbakova, Ekaterina M. Sadovskaya, Vladislav A. Sadykov, Nikita F. Eremeev

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2 Citations (Scopus)

Abstract

Electrical conduction and oxygen diffusion mobility in the bixbyite (Ia3) and rhombohedral (R3) polymorphs of the Ln 6 MoO 12-Δ (Ln = Er, Tm, Yb; Δ = δ, δ1, δ2; δ1 > δ2) heavy lanthanide molybdates, belonging to new, previously unexplored classes of potential mixed (ionic-electronic) conductors, have been studied in the range of 200-900 °C. The oxygen self-diffusion coefficient in bixbyite (Ia3) Yb 6 MoO 12-δ phase estimated by the temperature-programmed heteroexchange with C 18 O 2 was shown to be much higher than that for rhombohedral (R3) RI (with large oxygen deficiency) and (R3) RII (with small oxygen deficiency) Ln 6 MoO 12-Δ (Ln = Tm, Yb; Δ = δ1; δ1 > δ2) oxides. According to the activation energy for total conduction in ambient air, 0.99, 0.93, and 1.01 eV in Er 6 MoO 12-δ , Tm 6 MoO 12-δ, and Yb 6 MoO 12-δ bixbyites, respectively, oxygen ion conductivity prevails in the range ∼200-500 °C. Oxygen mobility data for the rhombohedral Ln 6 MoO 12-Δ (Ln = Er, Tm, Yb; Δ = δ1, δ2) phases RI and RII indicate that the oxygen in these phases exhibits mobility at much higher temperatures, such as those above 600-700 °C. Accordingly, below 600-700 °C they have predominantly electronic conductivity. As shown by total conductivity study of Ln 6 MoO 12-δ (Ln = Er, Tm, Yb) bixbyites (Ia3) and rhombohedral phases Ln 6 MoO 12-Δ (Ln = Er, Tm, Yb; Δ = δ1, δ2) (R3) in dry and wet air, the proton conductivity contribution exists only in Ln 6 MoO 12-δ (Ln = Er, Tm, Yb) bixbyites up to 450-600 °C and decreases with a decreasing of the lanthanide ionic radius. The obtained data on the mobility of oxygen and the presence of proton contribution in bixbyites in the 300-600 °C temperature range make it possible to confirm unequivocally that Ln 6 MoO 12-δ (Ln = Er, Tm, Yb) bixbyites are mixed electron-proton conductors at these temperatures.

Original languageEnglish
Pages (from-to)4275-4288
Number of pages14
JournalInorganic Chemistry
Volume58
Issue number7
DOIs
Publication statusPublished - 1 Apr 2019

Keywords

  • FLUORITE-RELATED SUPERSTRUCTURE
  • RARE-EARTH
  • TRANSPORT-PROPERTIES
  • LN(6-X)MOO(12-DELTA) LN
  • CRYSTAL-CHEMISTRY
  • PHASE-EQUILIBRIA
  • SYSTEM
  • ION
  • X=0
  • ELECTROLYTES

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