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Off-center ions in crystals are substitutional impurity ions whose equilibrium position is shifted away from the regular lattice site. The magnitude of the shift typically ranges from 0.2 to 1.0 Å. There are two possible mechanisms that can cause impurity ion displacement.
In the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site and it is called a substitutional defect. The atom is not supposed to be anywhere in the crystal, and is thus an impurity.
Three major structures can be distinguished: substitutional Ni, [47] nickel-vacancy [48] and nickel-vacancy complex decorated by one or more substitutional nitrogen atoms. [46] The "nickel-vacancy" structure, also called "semi-divacancy" is specific for most large impurities in diamond and silicon (e.g., tin in silicon [49]). Its production ...
Fundamentally, the Hume-Rothery rules are restricted to binary systems that form either substitutional or interstitial solid solutions. However, this approach limits assessing advanced alloys which are commonly multicomponent systems. Free energy diagrams (or phase diagrams) offer in-depth knowledge of equilibrium restraints in complex systems.
Interstitial atoms (blue) occupy some of the spaces within a lattice of larger atoms (red) In materials science, an interstitial defect is a type of point crystallographic defect where an atom of the same or of a different type, occupies an interstitial site in the crystal structure.
During chemical vapor deposition of diamond, a small fraction of single substitutional nitrogen impurity (typically <0.5%) traps vacancies generated as a result of the plasma synthesis. Such nitrogen-vacancy centers are preferentially aligned to the growth direction.
Substitutional solid solution strengthening occurs when the solute atom is large enough that it can replace solvent atoms in their lattice positions. Some alloying elements are only soluble in small amounts, whereas some solvent and solute pairs form a solution over the whole range of binary compositions.
The filled circles represent larger substitutional impurities, which are driven across the slip plane during dynamic strain aging (shown by the arrow). Because solute diffusion is thermally activated, increases in temperature can increase the rate and range of diffusion around a dislocation core.