Question

Why postive ion occupyes the interstial postion then negative ion?

Answer 1

Frenkel defect: This type of defect is created when an ion leaves its lattice site and occupies an interstitial site. In this case the crystal remains electrically neutral because the number of anions and cations remain the same. Since there is no absence of ions from the lattice, the density remains the same. Frenkel defects generally occur in ionic compounds (i) which have low co-ordination number, and (ii) in which anions are much larger in size than the cations. These defects can be found in silver halides (such as AgCI, AgBr or Agl) because of small size of the Ag+ ion, it can go into the interstitial sites.

This defect arise when an ion occupies an interstitial position between the lattice points. This defect occurs generally in ionic crystals in which the anion is much larger in size than the cation. ... The crystal remains neutral since the number of positive ions is the same as the number of negative ions.

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