Oxygen transport in nanostructured lanthanum manganites

Abstract

Methods and models describing oxygen diffusion and desorption in oxides have been developed for slightly defective and well crystallised bulky materials. Does nanostructuring change the mechanism of oxygen mobility? In such a case, models should be properly checked and adapted to take into account new material properties.In order to do so, temperature programmed oxygen desorption and thermogravimetric analysis, either in isothermal or ramp mode, have been used to investigate some nanostructured La 1-x A x MnO 3±δ samples (A=Sr and Ce, 20-60 nm particle size) with perovskite-like structure. The experimental data have been elaborated by means of different models to define a set of kinetic parameters able to describe oxygen release properties and oxygen diffusion through the bulk. Different rate-determining steps have been identified, depending on the temperature range and oxygen depletion of the material. In particular, oxygen diffusion shows rate-limiting at low temperature and with low defect concentration, whereas oxygen recombination at the surface seems to be the rate-controlling step at high * Corresponding author: Fax: +39-02-50314300; e-mail: ilenia.rossetti@unimi.it 2 temperature. However, the oxygen recombination step is characterised by an activation energy much lower than that for diffusion.In the present paper oxygen transport in nanosized materials is quantified by making use of widely diffused experimental techniques and by critically adapting to nanoparticles suitably chosen models developed for bulk materials.

Breakdown of kinetic compensation effect in physical desorption

“…These results are in stark contrast with previously reported strong coverage dependencies of the preexponential factor in the regime of strong interactions [17,19,20], which can result when the parameters are extracted through forced linearization [17,23,24]. Partial compensation has been previously considered [1,3], but this notion is not as widespread as that of a complete KCE; here we also observe that the partial compensation effect is not incompatible with the occurrence of curved Arrhenius plots, also referred to as non-Arrhenius behavior [18,21,33,34].…”

Oxygen Reduction Mechanisms in Nanostructured La0.8Sr0.2MnO3 Cathodes for Solid Oxide Fuel Cells

“…However, there are two important facts reported in the literature that clearly demonstrate that nanostructured LSM cathodes deserve great attention. On the one hand, studies by the isotope exchange depth profiling technique using SIMS depth profiling on microcrystalline LaMnO 3 and LSM show that diffusion of oxygen is much faster along grain boundaries than through the bulk. , On the other hand, recent studies on LSM thin films and nanopowders have reached to the same conclusion and, in addition, a faster oxygen exchange kinetics has been observed. , …”

Perovskite Strontium Doped Rare Earth Manganites Nanocomposites and Their Photocatalytic Performances

“…Oxygen diffusion and desorption in oxides have been developed for slightly defective and well crystallized bulky materials in Ref. [68]. The relation between nanostructure and the change of the mechanism of oxygen mobility has been studied in this work.…”