Browsing by Author "Patrakeev, MV"

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    Chemically induced expansion of La2NiO4+ δ-based materials
    (American Chemical Society, 2007-03-21) Kharton, VV; Kovalevsky, AV; Avdeev, M; Tsipis, EV; Patrakeev, MV; Yaremchenko, AA; Naumovich, EN; Frade, JR
    The equilibrium chemical strains induced by the oxygen hyperstoichiometry variations in mixed-conducting La2Ni1-xMxO4+δ (M = Fe, Co, Cu; x = 0−0.2) with K2NiF4-type structure, were studied by controlled-atmosphere dilatometry at 923−1223 K in the oxygen partial pressure range 5 × 10-4 to 0.7 atm. In combination with the oxygen content measured by coulometric titration and thermogravimetry, the results reveal a very low chemical expansivity, favorable for high-temperature electrochemical applications. Under oxidizing conditions, the isothermal expansion relative to atmospheric oxygen pressure (εC) is less than 0.02%. The ratio between these values and the corresponding nonstoichiometry increment varies from −3 × 10-3 to 6 × 10-3, which is much lower compared to most permeable mixed conductors derived from perovskite-like cobaltites and ferrites. Consequently, the chemical contribution to apparent thermal expansion coefficients at a fixed oxygen pressure, (13.7−15.1) × 10-6 K-1, does not exceed 5%. The high-temperature X-ray diffraction studies showed that this behavior results from strongly anisotropic expansion of the K2NiF4-type lattice, namely the opposing variations of the unit-cell parameters on changing oxygen stoichiometry. © 2007, American Chemical Society
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    Oxygen nonstoichiometry, chemical expansion, mixed conductivity, and anodic behavior of Mo-substituted Sr3Fe2O7-δ
    (Elsevier, 2010-07-26) Kharton, VV; Patrakeev, MV; Tsipis, EV; Avdeev, M; Naumovich, EN; Anikina, PV; Waerenborgh, JC
    The incorporation of molybdenum in the Ruddlesden-Popper type Sr3Fe2-xMoxO7-δ (x = 0–0.1) decreases oxygen deficiency, thermal expansion and electron-hole transport, and increases n-type electronic conductivity in reducing atmospheres. The oxygen ionic conduction remains essentially unaffected by doping. The equilibrium p(O2)–T–δ diagram of Sr3Fe1.9Mo0.1O7-δ, collected in oxygen partial pressure ranges from 10− 20 to 0.7 atm at 973–1223 K, can be adequately described by a defect model accounting for the energetic nonequivalence of apical O1 and equatorial O3 sites in the layered structure, in combination with iron disproportionation and stable octahedral coordination of Mo6+ and Mo5+ cations. The calculated enthalpy of anion exchange between the O1 and O3 positions, 0.49–0.51 eV, is in agreement with the values predicted by the atomistic computer simulation technique. The high-temperature X-ray diffraction studies showed a strongly anisotropic expansion of the Ruddlesden-Popper lattice on reduction, leading to very low chemical strains favorable for electrochemical applications. At 298–1223 K and oxygen pressures from 10− 8 to 0.21 atm, the linear thermal expansion coefficient of Sr3Fe1.9Mo0.1O7-δ varies in the narrow range (12.9–14.2) × 10− 6 K− 1. The relatively low level of n-type electronic conductivity leads, however, to a poor performance of porous Sr3Fe1.9Mo0.1O7-δ anodes in contact with lanthanum gallate-based solid electrolyte under reducing conditions. © 2010, Elsevier Ltd.