Abstract
Nanoparticles formed on oxide surfaces are of key importance in many fields such as catalysis and renewable energy. Here, we control B-site exsolution via lattice strain to achieve a high degree of exsolution of nanoparticles in perovskite thin films: more than 1100 particles μm−2 with a particle size as small as ~5 nm can be achieved via strain control. Compressive-strained films show a larger number of exsolved particles as compared with tensile-strained films. Moreover, the strain-enhanced in situ growth of nanoparticles offers high thermal stability and coking resistance, a low reduction temperature (550 °C), rapid release of particles, and wide tunability. The mechanism of lattice strain-enhanced exsolution is illuminated by thermodynamic and kinetic aspects, emphasizing the unique role of the misfit-strain relaxation energy. This study provides critical insights not only into the design of new forms of nanostructures but also to applications ranging from catalysis, energy conversion/storage, nano-composites, nano-magnetism, to nano-optics.
Highlights
To date, the studies of such exsolution processes have been performed predominantly in bulk polycrystalline ceramics
We have demonstrated a wide tunability of particle growth in strained films
We have further investigated the tunability of exsolution in thin films by controlling the reducing conditions such as reduction temperature and time (Fig. 3b, c and Supplementary Figure 6)
Summary
The studies of such exsolution processes have been performed predominantly in bulk polycrystalline ceramics. Thin-film heterostructures can induce a lattice strain because of the lattice mismatch between a substrate and a film, which affects many physical properties such as ferroelectricity, electron mobility, ionic conductivity, and electrocatalysis[17,18,19,20]. We demonstrate an unprecedently high degree of exsolution of nanoparticles in lattice misfit strained epitaxial thin films and achieve a particle density as high as ~1100 particles μm−2, with a size of only ~5 nm, at a temperature as low as 550 °C. Compressive-strained films show a larger number of exsolved metal particles than tensile-strained films. We have demonstrated a wide tunability of particle growth in strained films. Manipulation of nanoparticle structures using these concepts can be further applied to develop nano-composite functional films[25, 26], nano-phase magnetic materials[27,28,29], and nano-optics[30]
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