Oxygen-Storage Materials BaYMn₂O_5+δ from the Quantum-Chemical Point of View

Abstract

The experimentally known perovskite-like materials BaYMn2O5+δ (δ = 0, 0.5, 1) are characterized by a remarkably reversible oxygen-storage capacity at a moderate 500 °C. We try to elucidate the local structures of the vacancy arrangements in these compounds taking place after an oxygen release. This is done for the three compounds with the help of both ab initio total-energy calculations of density-functional quality and using classical structure rationale. Our results are compared with experimental structure findings. We further calculate oxygen-vacancy formation energies and predict the pathways of the oxygen atoms through the crystal by using NEB (nudged elastic band) calculations. Structure diagrams of the most likely energy pathways for oxygen migration are presented. Finally, thermodynamic considerations of the oxygen intake are carried out based on quasiharmonic phonon calculations and compared with experimental data. The theoretical molar reaction enthalpy for oxidizing BaYMn2O5 to BaYMn2O6 matches the experimental value.

Redox behavior of the SOFC electrode candidate NdBaMn2O5+δ investigated by high-temperature in situ neutron diffraction: first characterisation in real time of an LnBaMn2O5.5 intermediate phase

“…% of Icma NdBaMn2O5.5 impurity. Fast oxidation has been explained by its strong exothermicity (with respect to endothermic reduction) causing local overheating of the material speeding up oxygen diffusion in the bulk 39 . Figure 17.…”

Crystal structure and oxygen storage properties of BaLnMn2O5+δ (Ln: Pr, Nd, Sm, Gd, Dy, Er and Y) oxides

“…Nevertheless, it is well known that the reduction process (even in a relatively strong reducing atmosphere of 5 vol.% H 2 in Ar at 500 C [1,14,15]) takes much longer time (minutes), comparing to the oxidation (seconds). The origin of this behavior stems from the fact that the oxidation is rather strongly exothermic (DH % À220 kJ mol À1 for BaYMn 2 O 5 [16]), which causes local over-heating of the material, speeding up the diffusion of the oxygen in the bulk.…”

“…Recently, also BaLnMn 2 O 5+d perovskite-type oxides gained scientific interest in terms of their applicability as oxygen storage materials [1,[14][15][16]. As reported by Motohashi et al, the BaYMn 2 O 5 -BaYMn 2 O 6 system with a theoretical capacity equal to 3.85 wt.% shows high reversibility and practical capacity $3.7 wt.% at 500 C. This system shows reduced temperatures of reduction and oxidation processes, and fast kinetics of changes of d occurring at 500 C [1].…”

“…In addition, depending on the Ln cation size, B-site rock salt-type cation ordering also occurs in BaLnMn 2 O 5+d , giving rise to quite a complicated electronic structure diagram [20][21][22]24]. Oxygen anions, occupying positions within Ln-related layer can be extracted from the material relatively easy, and as was shown for BaYMn 2 O 5+d , reduced BaYMn 2 O 5 and BaYMn 2 O 5.5 compounds exist, with structure originating from removal of all (for O 5 ) and every other (for O 5.5 ) oxygen from the mentioned positions [4,16,25].…”

Quantum Chemical Design of Doped Ca2MnAlO5+δ as Oxygen Storage Media

“…26−28 It is also comparable to the diffusion in other OSMs such as BaYMnO 6 , which has a barrier of approximately 0.70 eV. 29 These comparisons imply that the mobility of oxygen vacancy in Ca 2 MnAlO 5.5 is sufficient to support quick-release kinetics. Indeed, it was observed experimentally that the release of oxygen happens nearly without any noticeable hysteresis once the operating conditions (temperature or O 2 partial pressure) shifts.…”