Vacancy interstitial pair

The defects generated in ion—soHd interactions influence the kinetic processes that occur both inside and outside the cascade volume. At times long after the cascade lifetime (t > 10 s), the remaining vacancy—interstitial pairs can contribute to atomic diffusion processes. This process, commonly called radiation enhanced diffusion (RED), can be described by rate equations and an analytical approach (27). Within the cascade itself, under conditions of high defect densities, local energy depositions exceed 1 eV/atom and local kinetic processes can be described on the basis of ahquid-like diffusion formalism (28,29). 

The ES-mechanism of Frenkel-pair formation as a result of excitation of Rydberg atomic states was confirmed by recent molecular dynamics calculations [28,29]. After the bubble formation the surrounding ground state atoms appear to have moved to the second shell. It was found that the second-nearest neighboring vacancy-interstitial pairs could create the permanent defects, which remain in the lattice after exciton annihilation (Fig.Sb) [29],... 

We mentioned above the collision cascade producing displaced atoms in a solid target. If we consider a single collision event in a crystalline solid, we can see that this displacement of atoms leads to the preferential formation of point defects. The most important types of point defects are a single vacancy (one atom or ion is missing), a single interstitial (an additional atom), a vacancy-interstitial pair (Frenkel pair). 

Figure 12.8 Binary ionic crystal showing defects that can lead to lattice diffusion, (a) Frenkel defect vacancy-interstitial pair), (b) Schottky defect (anion-cation vacancy). (After Kingery ct a .. 1976.)...

For Si, there are three types of native defects the vacancy, the interstitial, and the interstitialcy. The vacancy, V, is an empty lattice site. Depending on the configuration of the unsatisfied bonds due to the missing atom, a vacancy in Si can be either neutral, negatively or positively charged. A vacancy is also referred to as a Schottky defect. A Si atom residing in the interstices of the Si lattice is defined as a self-interstitial. A Frenkel pair is a vacancy-interstitial pair formed when an atom is displaced from a lattice site to an interstitial site. An interstitialcy... 

In compound crystals, balanced-defect reactions must conserve mass, charge neutrality, and the ratio of the regular lattice sites. In pure compounds, the point defects that form can be classified as either stoichiometric or nonstoichiometric. By definition, stoichiometric defects do not result in a change in chemistry of the crystal. Examples are Schottky (simultaneous formation of vacancies on the cation and anion sublattices) and Frenkel (vacancy-interstitial pair). 

The quotient of electrical conductivity a and thermal conductivity X is inversely proportional to the temperature. The ionic conductivity of solids depends on the lattice type and the type of the defects. The conductivity increases with temperature. This property is used to distinguish the ion conductor from the electron conductor. For vacancies and interstitials in the ion lattice, conductivity depends on the formation enthalpy for vacancy-interstitial pairs, Afo v. 

The formation of a PKA as a result of particle impingement is equivalent to the formation of a vacancy-interstitial pair lattice defect, and is a basic structural defect... 

Ko within which any vacancy-interstitial pair will spontaneously recombine and (ii) to subthreshold energy transfers inducing athermal migration and annihilation of interstitials (with a cross-section Frenkel-pair production rate obeys the following relation ... 

The extent of reaction for this process is determined by a trade-off between enthalpy and entropy. The perfect lattice is energetically favorable. To form this vacancy-interstitial pair, we need to overcome the bond energy of a zinc atom in its lattice site. However, when the crystal exists in a perfectly ordered lattice, every atom has a designated place to be it can have only one configuration. Therefore, its entropy is low. Formation of... 

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