Unveiling the Mechanism of Exsolution of Silver Nanoparticles for Decorating Lanthanum Strontium Ferrite

Abstract

Lanthanum strontium ferrite (La_0.85–xSr_0.15Ag_xFeO_3−δ x = 0; LSFO) and its silver-doped derivative (La_0.85–xSr_0.15Ag_xFeO_3−δ x = 0.05; LASFO) are synthesized using mild conditions by a sol–gel method. Both oxides present a perovskite-like structure with orthorhombic symmetry due to octahedral tilting; thus, the incorporation of silver in the A-site does not significantly modify the perovskite structure. Exsolution of silver nanoparticles (AgNPs) from LASFO is induced under mild conditions, resulting in Ag@LSFO samples. X-ray absorption spectroscopy and synchrotron X-ray diffraction data reveal that the mechanism of exsolution involves the reduction of Ag⁺ and the concomitant release of oxygen, without altering the oxidation state of Fe, inducing the formation of oxygen vacancies in the perovskite matrix. Homogeneous distribution of AgNPs on the perovskite matrix is observed by high-resolution transmission electron microscopy. The thermal evolution of Ag@LSFO proceeds through the progressive increase in oxygen vacancies that become thermally disordered. The study clarifies the mechanism of silver exsolution and the structural changes in lanthanum–strontium ferrite perovskites, providing insights into their potential use in catalytic and energy-related applications.