Browsing by Author "Knotko, AV"
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- ItemComparative study of electrical conduction and oxygen diffusion in the rhombohedral and bixbyite Ln6MoO12 (Ln = Er, Tm, Yb) polymorphs(American Chemical Society, 2019-03-19) Shlyakhtina, AV; Lyskov, NV; Avdeev, M; Goffman, VG; Gorshkov, NV; Knotko, AV; Kolbanev, IV; Karyagina, OK; Maslakov, KI; Shcherbakova, LG; Sadovskaya, EM; Sadykov, VA; Eremeev, NFElectrical conduction and oxygen diffusion mobility in the bixbyite (Ia3̅) and rhombohedral (R3̅) 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 (Ia3̅) Yb6MoO12−δ phase estimated by the temperature-programmed heteroexchange with C18O2 was shown to be much higher than that for rhombohedral (R3̅) RI (with large oxygen deficiency) and (R3̅) 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 (Ia3̅) and rhombohedral phases Ln6MoO12−Δ (Ln = Er, Tm, Yb; Δ = δ1, δ2) (R3̅) 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. © 2019 American Chemical Society
- ItemInterstitial oxide ion conduction in (Ln (2-x) Zrx) Zr2O7+ delta (Ln= Nd, Sm)(International Union of Crystallography, 2012-08-29) Shlyakhtina, AV; Belov, DA; Knotko, AV; Avdeev, M; Kolbanev, IV; Streletskii, AN; Shcherbakova, LGWe have studied the structure and transport properties of (Ln2-xZrx)Zr2O7+x/2 (Ln= Nd, Sm; x=0; 0.2; 0.32; 0.39; 0.48; 0.67; 0.78; 0.96; 1.14; 1.27) solid solutions, which lie in the ZrO2-Ln2Zr2O7 (Ln= Nd, Sm) isomorphous miscibility range (33.3, 29, 26.6, 25.3, 23.5, 20, 18, 15, 12, 10 mol% Ln2O3) in the Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO) systems. Major attention has been focused on the structure and properties of pyrochlore-like (Ln2 xZrx)Zr2O7+x/2 (Ln=Nd, Sm) solid solutions with x = 0–0.78, which are thought to be potential interstitial oxide ion conductors. The crystal structure of the solid solutions has been investigated by X-ray and neutron diffraction techniques using Rietveld refinement, and their microstructure has been examined by SEM. The excess oxygen content of the (Ln2-xZrx)Zr2O7+x/2 (Ln= Nd, Sm; x=0.2;0.32) pyrochlore-like solid solutions has been determined by thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The transport properties of the solid solutions in the two systems have been studied by impedancespectroscopy in air. © International Union of Crystallography
- ItemOxide ion transport in (Nd2−xZrx)Zr2O7+δ electrolytes by an interstitial mechanism(Elsevier, 2014-08-05) Shlyakhtina, AV; Belov, DA; Knotko, AV; Avdeev, M; Kolbanev, IV; Vorobieva, GA; Karyagina, OK; Shcherbakova, LGWe have studied the structure and transport properties of ten (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions, which lie in the ZrO2–Nd2Zr2O7 isomorphous miscibility range. Major attention has been focused on the pyrochlore-like (Nd2−xZrx)Zr2O7+x/2 solid solutions with x = 0–0.78, which are thought to be potential interstitial oxide ion conductors. The X-ray and neutron diffraction results demonstrate that the (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions undergo an order–disorder (pyrochlore–defect fluorite) structural phase transition. The (Nd2−xZrx)Zr2O7+x/2 (x = 0.2–0.78) have the bulk conductivity, ∼(1.2–4) × 10–3 S/cm at 750 °C, which is two orders of magnitude higher than that of the ordered pyrochlore Nd2Zr2O7. An attempt has been made to determine the interstitial oxygen content of (Nd2−xZrx)Zr2O7+x/2 (x = 0.2; 0.67) in a reducing atmosphere using thermogravimetry and mass spectrometry. It has been shown that no reduction occurs in the NdZrO system, where neodymium has only one oxidation state, 3+. © 2014, Elsevier B.V.