Interstitial defect

About: Interstitial defect is a research topic. Over the lifetime, 2511 publications have been published within this topic receiving 53834 citations.

Native point defects in ZnO

Abstract: We have performed a comprehensive first-principles investigation of native point defects in ZnO based on density functional theory within the local density approximation (LDA) as well as the $\mathrm{LDA}+U$ approach for overcoming the band-gap problem. Oxygen deficiency, manifested in the form of oxygen vacancies and zinc interstitials, has long been invoked as the source of the commonly observed unintentional $n$-type conductivity in ZnO. However, contrary to the conventional wisdom, we find that native point defects are very unlikely to be the cause of unintentional $n$-type conductivity. Oxygen vacancies, which have most often been cited as the cause of unintentional doping, are deep rather than shallow donors and have high formation energies in $n$-type ZnO (and are therefore unlikely to form). Zinc interstitials are shallow donors, but they also have high formation energies in $n$-type ZnO and are fast diffusers with migration barriers as low as $0.57\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$; they are therefore unlikely to be stable. Zinc antisites are also shallow donors but their high formation energies (even in Zn-rich conditions) render them unlikely to be stable under equilibrium conditions. We have, however, identified a different low-energy atomic configuration for zinc antisites that may play a role under nonequilibrium conditions such as irradiation. Zinc vacancies are deep acceptors and probably related to the frequently observed green luminescence; they act as compensating centers in $n$-type ZnO. Oxygen interstitials have high formation energies; they can occur as electrically neutral split interstitials in semi-insulating and $p$-type materials or as deep acceptors at octahedral interstitial sites in $n$-type ZnO. Oxygen antisites have very high formation energies and are unlikely to exist in measurable concentrations under equilibrium conditions. Based on our results for migration energy barriers, we calculate activation energies for self-diffusion and estimate defect-annealing temperatures. Our results provide a guide to more refined experimental studies of point defects in ZnO and their influence on the control of $p$-type doping.

Relations between the Concentrations of Imperfections in Crystalline Solids

Abstract: Publisher Summary The chapter presents a study on relations between the concentrations of imperfections in crystalline solids. Many properties of crystalline solids, such as the electronic or ionic conductivity, the color, the luminescence, and the magnetic susceptibility are determined by the presence of imperfections. Generally, six types of primary imperfections are distinguished; namely phonons, electrons and holes, excitons, vacant lattice sites and interstitial atoms or ions, foreign atoms or ions in either interstitial or substitutional positions, and dislocations. In addition atoms of the base crystal may be present at lattice sites normally occupied by other atoms. Five types of primary imperfections—namely, electrons and holes, vacant lattice sites, interstitials, misplaced lattice atoms, and foreign atoms—are discussed in this chapter. The chapter presents a new treatment of these problems by making use of a graphical representation. This treatment, together with the use of a band scheme for the electronic energy levels, greatly facilitates the application of the theory and the deduction of conclusions from it. Apart from a few exceptions, binary nonmetallic compounds of the formula M X will be considered almost exclusively. Here M indicates an element of a more electropositive character (metal) and X an element of a more electronegative character.

Metastable alumina polymorphs : Crystal structures and transition sequences

Abstract: The available literature on the crystal structure of the metastable alumina polymorphs and their associated transitions is critically reviewed and summarized. All the metastable alumina structures have been identified as ordered or partially ordered cation arrays on the interstitial sites of an approximately close-packed oxygen sublattice (either face-centered cubic or hexagonal close packed). The analysis of the symmetry relations between reported alumina polymorphs having an approximately face-centered cubic packing of the oxygen anions allows for an exact interpretation of all the complex domain structures that have been observed experimentally. Possible mechanisms for the phase transitions between the different alumina polymorphs also are discussed.

Transition metals in silicon

Abstract: A review is given on the diffusion, solubility and electrical activity of 3d transition metals in silicon. Transition elements (especially, Cr, Mn, Fe, Co, Ni, and Cu) diffuse interstitially and stay in the interstitial site in thermal equilibrium at the diffusion temperature. The parameters of the liquidus curves are identical for the Si:Ti — Si:Ni melts, indicating comparable silicon-metal interaction for all these elements. Only Cr, Mn, and Fe could be identified in undisturbed interstitial sites after quenching, the others precipitated or formed complexes. The 3d elements can be divided into two groups according to the respective enthalpy of formation of the solid solution. The distinction can arise from different charge states of these impurities at the diffusion temperature. For the interstitial 3d atoms remaining after quenching, reliable energy levels are established from the literature and compared with recent calculations.

N-doped TiO2: Theory and experiment

Abstract: Nitrogen doped titanium dioxide is attracting a continuously increasing attention because of its potential as material for environmental photocatalysis In this paper we review experimental and theoretical work done on this system in our groups in recent years The analysis is largely based on electron paramagnetic resonance (EPR) spectra and on their interpretation based on high-level ab initio calculations N-doped anatase TiO2 contains thermally stable single N-atom impurities either as charged diamagnetic Nb- centers or as neutral paramagnetic Nb centers (b stays for bulk) The N-atoms can occupy both interstitial or substitutional positions in the solid, with some evidence for a preference for interstitial sites All types of Nb centers give rise to localized states in the band-gap of the oxide, thus accounting for the related reduction of absorption band edge The relative abundance of these species depends on the oxidation state of the solid In fact, upon reduction, oxygen vacancies form and transfer electrons from Ti3+ ions to the Nb with formation of Ti4+ and Nb- EPR spectra measured under irradiation show that the Nb centers are responsible for visible light absorption with promotion of electrons from the localized N-impurity states to the conduction band or to electron scavengers like O2 adsorbed on the surface These results provide an unambiguous characterization of the electronic states associated with N-impurities in TiO2 and a realistic picture of the processes occurring in the solid under irradiation with visible light