A determination of the oxygen non-stoichiometry of the oxygen storage materials LnBaMn(2)O(5+delta) (Ln = Gd, Pr)

作者：Jeamjumnunja Kannika; Gong Wenquan; Makarenko Tatyana; Jacobson Allan J^*

来源：Journal of Solid State Chemistry, 2016, 239: 36-45.

DOI：10.1016/j.jssc.2016.04.006

• Oxygen storage material
• Double perovskite oxide
• Gadolinium barium manganese oxide
• Praeseodymium barium manganese oxide
• Oxygen non-stoichiometry

The A-site ordered double-perovskite oxides, LnBaMn(2)O(5+delta) (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 YBaMn2O5+delta. The results clearly reveal that changing the Ln cation strongly influences the oxidation/reduction behavior of LnBaMn(2)O(5+delta). Based on thermogravimetric analysis data, oxygen uptake begins at lower temperatures in both air and oxygen in compounds with Ln(3+) ions larger than Y3+. 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 GdBaMn2O5+delta and PrBaMn2O5+delta were determined as a function of pO(2) at 600, 650, 700 and 750 degrees C by Coulometric titration at near-equilibrium conditions. The results confirm that these materials have two distinct phases on oxidation/reduction with delta approximate to 0, 0.5 and a third phase with a range of composition with an oxygen content (5+delta) approaching similar to 6. The stabilities of the LnBaMn(2)O(5+delta) phases extend over a wide range of oxygen partial pressures (similar to 10(-25) <= pO(2) (atm) <=similar to 1) depending on temperature. Isothermal experiments show that the larger the Ln3+ cation the lower pO(2) for phase conversion. At some temperatures and pO(2) conditions, the LnBaMn(2)O(5+delta) compounds are unstable with respect to decomposition to BaMnO3-delta 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.

• 出版日期2016-7