The paramagnetic defects present in pristine zirconium dioxide (ZrO2) and those formed upon reductive treatments (either annealing or UV irradiation in H2) are described and rationalized by the joint use of electron paramagnetic resonance (EPR) and DFT supercell calculations. Three types of Zr3+ reduced sites have been examined both in the bulk of the solid (one center) and at the surface (two centers). Trapping electron centers different from reduced Zr ions are also present, whose concentration increases upon annealing. A fraction of these sites are paramagnetic showing a symmetric signal at g = 2.0023, but the majority of them are EPR silent and are revealed by analysis of electron transfer from the reduced solid to oxygen. The presence of classic F-type centers (electrons in bulk oxygen vacancies) is disregarded on the basis of the g-tensor symmetry. This is expected, on the basis of theoretical calculations, to be anisotropic and thus incompatible with the observed signal. In general terms, ZrO2 has some properties similar to typical reducible oxides such as TiO2 and CeO2 (excess electrons stabilized at cationic sites), but it is much more resistant to reduction than this class of materials. While point defects in doped (Y3+, Ca2+) ZrO2 materials have been widely investigated for their role as ionic conductors, the defectivity of pristine ZrO2 is much less known; this paper presents a thorough analysis of this phenomenon.

The dispersion of small amounts of Ce 4+ ions in the bulk of ZrO 2 leads to a photoactive material sensitive to visible light. This is shown by monitoring with EPR the formation and the reactivity of photogenerated (λ > 420 nm) charge carriers. The effect, as confirmed by DFT calculations, is due to the presence in the solid of empty 4f Ce states at the mid gap, which act as intermediate levels in a double excitation mechanism. This solid can be considered an example of a third-generation photoactive material.

Time-dependent density functional theory (TDDFT) was used to calculate the optical absorption spectra of gold clusters of 20–171 atoms. The spectra for the smallest clusters agree with previous results, and the spectra for the largest clusters show features consistent with classical Mie theory. The systematic exploration of particles of sizes within these two extremes has allowed the trends linking optical absorption spectra and particle size and symmetry to be identified. A transition from molecular-like spectra to a more classical response is observed.

The optical absorption of bare and ligand-coated Au 55 and Au 69 "Schmid" clusters was calculated using time-dependent density functional theory (TDDFT). Calculations were performed using the explicit time propagation method with the local density approximation (LDA) for the exchange-correlation potential. Both icosahedral and cuboctahedral structures of the Au 55 gold core were simulated. The ligand coating was shown to have the effect reducing the features of the optical absorption spectrum of the clusters, giving a profile more similar to experimental results. The difference in the optical absorption between the different geometries and core sizes is also less marked when the clusters are coated. The results suggest that within the 1.4 nm size range, the absorption spectra are dominated by the coating and are not experimentally distinguishable. Binding energies were also calculated for the Au 55 cluster, showing that the cuboctahedral structure has lower energy although the energy difference is very small.The effect of the coating on the electron density of the gold cluster is also investigated by subtracting the electron densities of the bare clusters from those of the coated clusters.

Pulsed cathodic arc and pulsed magnetron sputtered WO3 thin films were investigated using electron microscopy. It was found that the cathodic arc deposited material consisted of the α-WO3 phase with a high degree of crystallinity. In contrast, the magnetron sputtered material was highly disordered making it difficult to determine its phase. Electron energy-loss spectroscopy was used to study the oxygen K edge of the films and it was found that the near-edge fine structures of films produced by the two deposition methods differed. The oxygen K-edge near-edge structures for various phases of WO3 were calculated using two different self-consistent methods. Each phase was found to exhibit a unique oxygen K edge, which would allow different phases of WO3 to be identified using x-ray absorption spectroscopy or electron energy-loss spectroscopy. Both calculation methods predicted an oxygen K edge for the γ-WO3 phase which compared well to previous x-ray absorption spectra. In addition, a close match was found between the oxygen K edges obtained experimentally from the cathodic arc deposited material and that calculated for the α-WO3 phase.