Oxide nanoparticle exsolution in Lu-doped (Ba,La)CoO3

Abstract

This study investigated Lu doping of Ba_0.5La_0.5CoO₃ and its influence on the exsolution of oxide nanoparticles (NPs). As a result of Lu doping, we observed the phase segregation into the main Ba_0.4La_0.6Co_0.85Lu_0.15O₃ (BLCO–Lu) phase and the secondary Ba_0.85La_0.15Co_0.75Lu_0.25O₃ (BCO–Lu) phase. We noticed the exsolution of BCO–Lu nanoparticles on the main BLCO–Lu phase. Moreover, the BLCO–Lu phase exsolved in the form of nanoparticles on the adjacent BCO–Lu grains. That shows that the phases are covered with mutually exsolved oxide NPs. In addition, trace amounts of the BaLuCo₄O₇ phase are detected. We noticed that the exsolved oxides even in the as-prepared sample were fine (average size of 18 nm), and well distributed with a dense population of NPs above 280 per 1 μm². Furthermore, we showed that the size and shape of the exsolved oxide NPs can be controlled by varying the annealing temperature. For example, at 800 °C the exsolved oxides segregate and form two different shapes; spherical and cuboidal, with an average size of 31 nm and NP population of about 23 NPs per μm². Meanwhile, with lowering the temperature to 400 °C the oxides form only spherical and quite evenly distributed NPs with the occurrence of 137 NPs per 1 μm². The obtained results open the possibility of tailoring a novel, more catalytically active material for future applications in electrochemical devices.