- Researchers develop an evolutionary algorithm to analyze different nanoparticle compositions.
- Some stable nanoparticles exhibit strange chemical compositions in normal conditions, whereas for macro objects, this usually happens in extreme conditions.
Nanoparticles are very different from macro objects — such as glasses and crystals — especially in terms of properties and chemical composition. Most of the nanoclusters possess a range of chemical and physical properties, as well as unique electronic and geometric structures.
Because of their tiny size, it is very difficult to extract their precise structural characteristics by experimental methods. That’s why many nanostructural models are inferred indirectly with the aid of theoretical procedures.
Now, researchers at the Moscow Institute of Physics and Technology have developed a new structure prediction algorithm named USPEX that can examine a variety of nanoparticle compositions. In particular, they have analyzed two types of nanoparticles necessary for catalysis: cerium-oxygen and iron-oxygen.
To study transition metal oxide clusters, the team applied USPEX algorithm, DFT+U, and thermodynamic approaches. For the first time, they examined ‘magic nanoclusters’ and filtered out those compositions that become thermodynamically favorable at given oxygen pressure and temperature.
They found that the so-called ‘magic nanoparticles’ that exhibit enhanced stability could have unusual chemical compositions, for example, Ce3O12, Ce5O6, Fe4O14, and Fe2O6.
Oxygen-rich nanoparticles like Ce3O12 were found to be stable at typical conditions, and like most oxide nanoparticles, they have the potential to cause cancer.
In this study, researchers performed numerous experiments to figure out how compositions vary by altering partial pressure and temperature of oxygen.
They noticed some changes in magnetic properties: for iron-oxygen clusters, the low-oxygen clusters (Fe6O4) are ferromagnetic, whereas high oxygen clusters (Fe4O14) are all antiferromagnetic.
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This shows that competition between ferromagnetism and antiferromagnetism plays a crucial role in controlling the stability of low-oxygen iron-oxygen clusters. At extreme oxygen pressures, magic nanoparticles consist of excess oxygen as peroxide and superoxide molecules stuck to their surface.
What Does It Mean?
Simply put, stable nanoclusters can exhibit unusual chemical compositions (for instance, Ce3O12 and Si4O18) in normal conditions. Whereas, in the case of crystals, this usually happens in extreme scenarios (at high temperatures and pressures).
Furthermore, the team found that magic clusters have virtually the same ridges, islands of stability, and seas of instability, just like atomic nuclei, which can also be described as clusters made of two kinds of particles: neutrons and proton (iron and oxygen in magic clusters).
As per the study, the topology of ridges and islands of stability could be a crucial parameter for determining the feasibility of a specific chemical transformation of a nanoparticle.