Explanation of Schottky defect, Frankel defect, Interstitial defect and F-centres.

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1. Schottky defect:- In this kind of defect equal number of cations and anions are missing from the crystal lattice. Due to this the vacant sites or the holes are present in the lattice. This kind of defect is present in the ionic compounds with high coordination number and equal size of ions.

Density of the crystal lattice decreases due to this defect.

For example NaCl, KBr and KCl .

2. Frankel defect:- This kind of defect arise due to the jumping of an ion from its lattice site to the interstitial space. Or simply leave its place and occupy the interstitial space. This kind of defect is seen in the compound with larger size of anion and small size of cation.

The overall density of crystal remains the same as there is no loss of any particle from the crystal lattice.

For example :- ZnS and AgBr.

3. Interstitial defect :- This kind of defect arise due to the presence of extra ions in the Interstitial sites they may be anions or the cations.

Due to this effect the density of the crystal increases, as the number of particles in the same volume has increased.

4. F-Centre :- This kind of defect is seen in case of crystals in which the anionic sites are occupied by the electrons . And presence of extra electron imparts colour to the crystal as the free electron can easily absorb energy and can jump to higher level.

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