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where N v is the vacancy concentration, Q v is the energy required for vacancy formation, k B is the Boltzmann constant, T is the absolute temperature, and N is the concentration of atomic sites i.e. = where ρ is density, N A the Avogadro constant, and M the molar mass. It is the simplest point defect.
For example, the defect may result in an ion on its own ion site or a vacancy on the cation site. To complete the reactions, the proper number of each ion must be present (mass balance), an equal number of sites must exist (site balance), and the sums of the charges of the reactants and products must also be equal (charge balance).
An F center is ionized and becomes a vacancy; the electron moves through the material to bind to another F center, which becomes an F − center. The electron vacancy moves through the material and ends up next to the F − center, which gives its electron back to the vacancy, forming two neighbouring F centers, i.e. an F 2 center.
Larger defects in an ordered structure are usually considered dislocation loops. For historical reasons, many point defects, especially in ionic crystals, are called centers: for example a vacancy in many ionic solids is called a luminescence center, a color center, or F-center. These dislocations permit ionic transport through crystals leading ...
The number of vacancies may also be influenced by the number of chemical impurities in the crystal lattice, if such impurities require the formation of vacancies to exist in the lattice. A vacancy can move through the crystal structure when the neighbouring particle "jumps" in the vacancy, so that the vacancy moves in effect one site in the ...
A Schottky defect is an excitation of the site occupations in a crystal lattice leading to point defects named after Walter H. Schottky. In ionic crystals , this defect forms when oppositely charged ions leave their lattice sites and become incorporated for instance at the surface, creating oppositely charged vacancies .
In chemistry, the terrace ledge kink (TLK) model, which is also referred to as the terrace step kink (TSK) model, describes the thermodynamics of crystal surface formation and transformation, as well as the energetics of surface defect formation. It is based upon the idea that the energy of an atom’s position on a crystal surface is ...
Since the fractional vacancy concentration is proportional to exp(− Q f ± σΩ / RT ), where Q f is the vacancy-formation energy, the vacancy concentration is higher in tensile regions than in compressive regions, leading to a net flow of vacancies from the regions under tension to the regions under compression, and this is equivalent ...