Klimkowicz, A.; Swierczek, K.; Zheng, K.; Wallacher, D.; Takasaki, A.: Oxygen release from BaLnMn2O6 (Ln: Pr, Nd, Y) under reducing conditions as studied by neutron diffraction. Journal of Materials Science 52 (2017), p. 6476-6485
10.1007/s10853-017-0883-2
Abstract:
Selected A-site cation-ordered BaLnMn2O6 were investigated by neutron diffraction technique in terms of the structural modification ongoing with the oxygen release during annealing in reducing conditions. Kinetics of the structural transformations between oxidized BaLnMn2O6 (O6), partially reduced BaLnMn2O5.5 (O5.5) and fully reduced BaLnMn2O5 (O5) were measured in 200–500 C range in 5 vol% H2 in Ar. Studies revealed that both O6–O5.5 and O5.5–O5 transitions for all samples occur according to a two-phase mechanism, but the phases undergo slight modification of their structural parameters. The Y-containing material showed decreased tendency of formation of oxygen vacancy-ordered BaYMn2O5.5. Moreover, kinetics of the transitions for Pr- and Nd-containing oxides was found to be more constrained by surface reaction and nucleation processes at the initial stage, while the following oxygen release from O5.5 phase was found to be limited rather by the oxygen diffusion, which is in opposite to BaYMn2O5?d. The obtained results indicate that ionic radius of Ln3? has a direct influence on the mechanism of the oxygen release process from BaLnMn2O6, influencing the oxygen storage-related performance.