Nanostructured Materials: an Experimental and Computational Study

ABSTRACT

In this thesis, experiment and atomistic simulations have been used in order to study the structure and properties of materials at the nanoscale focussing the attention, in particular, on metal oxide nanoparticles. Chapter 3 presents results on CuFe2O4-SiO2 nanocomposites where copper ferrite nanoparticles are embedded within a silica aerogel and xerogel matrix. In this case, extended X-ray absorption fine structure (EXAFS) spectroscopy has been extremely valuable in order to elucidate the cation distribution of the spinel. CeO2-SiO2 nanocomposites in form of aerogel and xerogel have been also synthesised and characterised. The CeO2 nanoparticles are either grown within the porous silica matrix (Chapter 4) or synthesised in advance by a hydrothermal method (Chapter 5). In order to enhance the reactivity, the attention has been focused on obtaining ceria cuboidal nanoparticles and on their dispersion in a silica aerogel matrix. An atomistic model of a CeO2 cuboidal nanoparticle has been then obtained using Molecular Dynamics (MD) simulations (Chapter 6), by performing the crystallisation of the nanoparticle with a new technique, involving the use of a crystalline seed, which drives the crystallisation to the cubic shape. The atomistic model has been found to be in quantitative agreement with experiment. The mechanical properties of CeO2 nanoparticles have been then calculated as a function of size, shape and microstructure, and are presented in Chapter 7. It has been found that the mechanical properties of CeO2 nanoparticles are dominated by the presence of grain boundaries. Furthermore, the simulations predict that Ostwald ripening can be induced along a ?11 grain boundary by applying uniaxial force.