We investigate, through first-principles calculations, the stability and electronic structure of self-interstitials and vacancies in both hexagonal (graphite-like) and cubic boron nitride. We find that the self-interstitials ${\mathrm{N}}_i$ and ${\mathrm{B}}_i$ in hexagonal boron nitride $(h-\mathrm{BN})$ have low formation energies, comparable to those of the vacancies $V_{\mathrm{N}}$ and $V_{\mathrm{B}}.$ For instance, we find that ${\mathrm{N}}_i$ is the most stable defect in $h-\mathrm{BN}$ under N-rich and p-type conditions followed by the nitrogen vacancy. This is consistent with experimental findings of large concentrations of nitrogen interstitials and vacancies, and of the trapping of nitrogen in the hexagonal phase of BN thin films grown by ion-bombardment assisted deposition techniques. In contrast, in cubic boron nitride $(c-\mathrm{BN})$ the self-interstitials have high formation energies as compared to those of the vacancies. As a consequence, the formation of vacancy-interstitial pairs in kickout processes would typically require much more energy in $c-\mathrm{BN}$ than in $h-\mathrm{BN}.$ This suggests that a possible role of the ion bombardment in favoring the growth of $c-\mathrm{BN}$ films is to generate a much larger amount of defects in the hexagonal phase than in the cubic phase.

We perform ab initio calculations, based on density functional theory, for substitutional and vacancy defects in the monoclinic hafnium oxide (m-HfO2) and α-quartz (SiO2). The neutral oxygen vacancies and substitutional Si and Hf defects in HfO2 and SiO2, respectively, are investigated. Our calculations show that, for a large range of Hf chemical potential, Si substitutional defects are most likely to form in HfO2, leading to the formation of a silicate layer at the HfO2/Si interface. We also find that it is energetically more favorable to form oxygen vacancies in SiO2 than in HfO2, which implies that oxygen-deficient HfO2 grown on top of SiO2 will consume oxygen from the SiO2.

Iron macrocyclic complexes (MN4) are promising catalysts for replacing platinum (the industrial standard) in electrocatalysis. In particular, FeN4 complexes have shown lower overpotential than Pt for the oxygen reduction reaction (ORR) in alkaline media. To predict the electrochemical activity of metal electrodes and molecular catalysts towards the ORR, reactivity descriptors with typical volcano correlation have been demonstrated. The most important are M–O₂ binding energy and M⁽ⁿ⁾⁺/M⁽ⁿ⁻¹⁾⁺ redox potentials for the complexes. We studied a new Fe complex, which possesses powerful electron-withdrawing fluorine residues at the periphery of the phthalocyanine ring. Fe hexadecafluorophthalocyanine (16(F)FePc) was characterized by electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) in the presence and in absence of O₂. Experimental and calculated O₂–Fe binding energies, as well as electrochemical characterization confirms the excellent activity of this complex for the ORR placing this complex at the top of the MN4 volcano correlation.