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Title: A determination of the oxygen non-stoichiometry of the oxygen storage material YBaMn{sub 2}O{sub 5+δ}

The A-site ordered double-perovskite oxide, YBaMn{sub 2}O{sub 5+δ}, has been of recent interest for possible application as an oxygen storage material. In the present study, the oxygen non-stoichiometry of YBaMn{sub 2}O{sub 5+δ} has been determined as a function of pO{sub 2} at 650, 700 and 750 °C by Coulometric titration at near-equilibrium conditions. The results confirm that this perovskite oxide has three distinct phases on oxidation/reduction with δ≈0, 0.5 and 1. The stabilities of the YBaMn{sub 2}O{sub 5+δ} phases span a wide range of oxygen partial pressures (∼10{sup −20}≤pO{sub 2}(atm)≤∼1 ) depending on temperature. The phases interconvert at higher pO{sub 2} values at higher temperatures. The partial molar free energies (Δμ{sub O}) corresponding to the oxidation of YBaMn{sub 2}O{sub 5} to YBaMn{sub 2}O{sub 5.5} and of YBaMn{sub 2}O{sub 5.5} to YBaMn{sub 2}O{sub ∼6} were determined. The value of Δμ{sub O} in both oxidation steps becomes less negative with increasing temperature. At some T and pO{sub 2} conditions, YBaMn{sub 2}O{sub 5+δ} is unstable with respect to decomposition to BaMnO{sub 3−δ} and YMnO{sub 3}. This instability is anticipated from the previous studies of the synthesis of YBaMn{sub 2}O{sub 5+δ} but is more apparent in the present experiments which are necessarily slow inmore » order to achieve equilibrium with respect to the oxygen content. - Highlights: • Determination of the oxygen non-stoichiometry of YBaMn{sub 2}O{sub 5+δ} as a function of pO{sub 2} and T. • Establishments of pO{sub 2} ranges of stability of O{sub 5} and O{sub 5.5} at 650 °C, 700 °C and 750 °C. • Discovery of the kinetic instability of YBaMn{sub 2}O{sub 5+δ} with respect to decomposition to BaMnO{sub 3}−{sub x} and YMnO{sub 3}. • Evaluation of the thermodynamics of the oxidation of YBaMnO{sub 5}.« less
Authors:
; ; ;
Publication Date:
OSTI Identifier:
22486828
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 230; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BARIUM COMPOUNDS; DECOMPOSITION; FREE ENERGY; MANGANATES; MANGANESE OXIDES; OXIDATION; OXYGEN; PARTIAL PRESSURE; PEROVSKITE; REDUCTION; STOICHIOMETRY; STORAGE; SYNTHESIS; THERMODYNAMICS; TITRATION; YTTRIUM COMPOUNDS