Abstract The A-site ordered double-perovskite oxides, LnBaMn 2 O 5+δ (Ln=Gd, Pr), were synthesize... more Abstract The A-site ordered double-perovskite oxides, LnBaMn 2 O 5+δ (Ln=Gd, Pr), were synthesized and investigated to understand the effect of A site cation substitution on the oxygen storage properties of these materials. The present results are compared with our previous data for YBaMn 2 O 5+δ . The results clearly reveal that changing the Ln cation strongly influences the oxidation/reduction behavior of LnBaMn 2 O 5+δ . Based on thermogravimetric analysis data, oxygen uptake begins at lower temperatures in both air and oxygen in compounds with Ln 3+ ions larger than Y 3+ . These oxides exhibit almost complete and reversible oxygen uptake/release between fully-reduced LnBaMn 2 O 5 and fully-oxidized LnBaMn 2 O 6 during changes of the oxygen partial pressure between air and 1.99% H 2 /Ar. In addition, the oxygen non-stoichiometries of GdBaMn 2 O 5+δ and PrBaMn 2 O 5+δ were determined as a function of pO 2 at 600, 650, 700 and 750 °C by Coulometric titration at near-equilibrium conditions. The results confirm that these materials have two distinct phases on oxidation/reduction with δ≈0, 0.5 and a third phase with a range of composition with an oxygen content (5+δ) approaching ~6. The stabilities of the LnBaMn 2 O 5+δ phases extend over a wide range of oxygen partial pressures (∼10 −25 ≤pO 2 (atm)≤∼1) depending on temperature. Isothermal experiments show that the larger the Ln 3+ cation the lower pO 2 for phase conversion. At some temperatures and pO 2 conditions, the LnBaMn 2 O 5+δ compounds are unstable with respect to decomposition to BaMnO 3−δ and LnMnO 3 . This instability is more apparent in Coulometric titration experiments than in thermogravimetric analysis. The Coulometric titration experiments are necessarily slow in order to achieve equilibrium oxygen compositions.
Abstract The A-site ordered double-perovskite oxides, LnBaMn 2 O 5+δ (Ln=Gd, Pr), were synthesize... more Abstract The A-site ordered double-perovskite oxides, LnBaMn 2 O 5+δ (Ln=Gd, Pr), were synthesized and investigated to understand the effect of A site cation substitution on the oxygen storage properties of these materials. The present results are compared with our previous data for YBaMn 2 O 5+δ . The results clearly reveal that changing the Ln cation strongly influences the oxidation/reduction behavior of LnBaMn 2 O 5+δ . Based on thermogravimetric analysis data, oxygen uptake begins at lower temperatures in both air and oxygen in compounds with Ln 3+ ions larger than Y 3+ . These oxides exhibit almost complete and reversible oxygen uptake/release between fully-reduced LnBaMn 2 O 5 and fully-oxidized LnBaMn 2 O 6 during changes of the oxygen partial pressure between air and 1.99% H 2 /Ar. In addition, the oxygen non-stoichiometries of GdBaMn 2 O 5+δ and PrBaMn 2 O 5+δ were determined as a function of pO 2 at 600, 650, 700 and 750 °C by Coulometric titration at near-equilibrium conditions. The results confirm that these materials have two distinct phases on oxidation/reduction with δ≈0, 0.5 and a third phase with a range of composition with an oxygen content (5+δ) approaching ~6. The stabilities of the LnBaMn 2 O 5+δ phases extend over a wide range of oxygen partial pressures (∼10 −25 ≤pO 2 (atm)≤∼1) depending on temperature. Isothermal experiments show that the larger the Ln 3+ cation the lower pO 2 for phase conversion. At some temperatures and pO 2 conditions, the LnBaMn 2 O 5+δ compounds are unstable with respect to decomposition to BaMnO 3−δ and LnMnO 3 . This instability is more apparent in Coulometric titration experiments than in thermogravimetric analysis. The Coulometric titration experiments are necessarily slow in order to achieve equilibrium oxygen compositions.
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Papers by Kannika JEAMJUMNUNJA