Amorphous aluminum oxide Al2O3 (a-Al2O3) layers grown by various deposition techniques contain a significant density of negative charges. In spite of several experimental and theoretical studies, the origin of these charges still remains unclear. We report the results of extensive density functional theory calculations of native defects-O and Al vacancies and interstitials, as well as H interstitial centers-in different charge states in both crystalline α-Al2O3 and in a-Al2O3. The results demonstrate that both the charging process and the energy distribution of traps responsible for negative charging of a-Al2O3 films (Zahid et al 2010 IEEE Trans. Electron Devices 57 2907) can be understood assuming that the negatively charged Oi and VAl defects are nearly compensated by the positively charged Hi, VO and Ali defects in as prepared samples. Following electron injection, the states of Ali, VO or Hi in the band gap become occupied by electrons and sample becomes negatively charged. The optical excitation energies from these states into the oxide conduction band agree with the results of exhaustive photo-depopulation spectroscopy measurements (Zahid et al 2010 IEEE Trans. Electron Devices 57 2907). This new understanding of the origin of negative charging of a-Al2O3 films is important for further development of nanoelectronic devices and solar cells.

Hard carbons are among the most promising materials for alkali‐ion metal anodes. These materials have a highly complex structure and understanding the metal storage and migration within these structures is of utmost importance for the development of next‐generation battery technologies. The effect of different carbon structural motifs on Li, Na, and K storage and diffusion are probed using density functional theory based on experimental characterizations of hard carbon samples. Two carbon structural models—the planar graphitic layer model and the cylindrical pore model—are constructed guided by small‐angle X‐ray scattering and transmission electron microscopy characterization. The planar graphitic layers with interlayer distance 6.5 Å, when the graphitic layer separation becomes so wide that there is negligible interaction between the two graphitic layers. The cylindrical pore model, reflecting the curved morphology, does not increase metal storage, but significantly lowers the metal migration barriers. Hence, the curved carbon morphologies are shown to have great importance for battery cycling. These findings provide an atomic‐scale picture of the metal storage and diffusion in these materials.

Hard carbon anodes have shown significant promise for next‐generation battery technologies. These nanoporous carbon materials are highly complex and vary in structure depending on synthesis method, precursors, and pyrolysis temperature. Structurally, hard carbons are shown to consist of disordered planar and curved motifs, which have a dramatic impact on anode performance. Here, the impact of position on defect formation energy is explored through density functional theory simulations, employing a mixed planar bulk and curved surface model. At defect sites close to the surface, a dramatic decrease ( $\ge$50%) in defect formation energy is observed for all defects except the nitrogen substitutional defect. These results confirm the experimentally observed enhanced defect concentration at surfaces. Previous studies have shown that defects have a marked impact on metal storage. This work explores the interplay between position and defect type for lithium, sodium, and potassium adsorption. Regardless of defect location, it is found that the energetic contributions to the metal adsorption energies are principally dictated by the defect type and carbon interlayer distance.

Understanding the effect of electric fields on defect creation and diffusion in metal oxides is of fundamental importance for developing accurate models of oxide degradation in electronic devices and dielectric breakdown. We use the Berry phase operator method within density functional theory to calculate how an applied electric field affects barriers for the creation of oxygen vacancy-interstitial defect pairs (DPs) and diffusion of interstitial O ions in monoclinic ($m$-)${\mathrm{HfO}}_2$. The results demonstrate that even close to breakdown fields, barriers for DP generation exceed 6 eV in the perfect $m-{\mathrm{HfO}}_2$ lattice. Simulated injection of extra electrons from electrodes significantly lowers barriers for the creation of DPs, which are further reduced by the field to around 1 eV. Thus, bias application facilitates the injection of electrons into the oxide; these extra electrons reduce energy barriers for the creation of O vacancies, and these barriers as well as those for O ion diffusion are further lowered by the field. We find that, within a linear regime, the electric field modulates the barrier height by a dot product between the electric field and the electric dipole at the zero-field transition state to good accuracy.

The effect of Co-site doping on the electronic, magnetic, and physical properties of next-generation SOFC cathode SmCoO ₃ .