Comparative Study of Electrical Conduction and Oxygen Diffusion in the Rhombohedral and Bixbyite Ln6MoO12 (Ln = Er, Tm, Yb) Polymorphs
| Autor: | V. G. Goffman, I. V. Kolbanev, A.V. Knotko, N.F. Eremeev, Maxim Avdeev, A.V. Shlyakhtina, Vladislav A. Sadykov, Nikolay V. Lyskov, Konstantin I. Maslakov, L. G. Shcherbakova, E.M. Sadovskaya, Olga K. Karyagina, N. V. Gorshkov |
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| Rok vydání: | 2019 |
| Předmět: |
Lanthanide
Ionic radius 010405 organic chemistry Chemistry Analytical chemistry chemistry.chemical_element Activation energy Conductivity Atmospheric temperature range 010402 general chemistry Bixbyite 01 natural sciences Oxygen 0104 chemical sciences Inorganic Chemistry Phase (matter) Physical and Theoretical Chemistry |
| Zdroj: | Inorganic Chemistry. 58:4275-4288 |
| ISSN: | 1520-510X 0020-1669 |
| Popis: | Electrical conduction and oxygen diffusion mobility in the bixbyite ( Ia3) and rhombohedral ( R3) polymorphs of the Ln6MoO12-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) Yb6MoO12-δ phase estimated by the temperature-programmed heteroexchange with C18O2 was shown to be much higher than that for rhombohedral ( R3) RI (with large oxygen deficiency) and ( R3) RII (with small oxygen deficiency) Ln6MoO12-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 Er6MoO12-δ, Tm6MoO12-δ, and Yb6MoO12-δ bixbyites, respectively, oxygen ion conductivity prevails in the range ∼200-500 °C. Oxygen mobility data for the rhombohedral Ln6MoO12-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 Ln6MoO12-δ (Ln = Er, Tm, Yb) bixbyites ( Ia3) and rhombohedral phases Ln6MoO12-Δ (Ln = Er, Tm, Yb; Δ = δ1, δ2) ( R3) in dry and wet air, the proton conductivity contribution exists only in Ln6MoO12-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 Ln6MoO12-δ (Ln = Er, Tm, Yb) bixbyites are mixed electron-proton conductors at these temperatures. |
| Databáze: | OpenAIRE |
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