Frankel and schottky defects

Definitions of Frankel and Schottky defects and difference between them.

1. G.G.S ADARSH SEN. SEC. SCHOOL SAHNEWALI TOPIC :- Frankel and Schottky Defect 1

2. If an ion left its lattice site (causing a vacancy or a hole there) and occupies the interstitial site, electrical neutrality as well as stoichiometry of the compound are maintained. This effect does not cause effect on density of crystal as no ion lefts the crystal. Examples of such compounds :- AgCl , AgBr , etc. Frankel Defects 2

3. Types of Compounds Exhibits F rankel Defects 3

4. The smaller ion lefts the lattice sits and shifted towards an interstitial site which cause a hole there. This is Frankel Defect 4

5. AgCl is an example of Frankel defect, in this Ag ions lefts their lattice site and moves towards interstitial site 5

6. Schottky Defect 6 In ionic crystals, the defect forms when oppositely charged ions leave their lattice sites, creating vacancies. These vacancies are formed in stoichiometry units , to maintain an overall neutral charge in the ionic solid. The vacancies are then free to move about as their own entities. Normally these defects will lead to a decrease in the density of the crystal . For examples in compounds :- NaCl , KCl   , AgBr etc.

7. Types of Compounds Exhibits Schottky Defects 7

8. In this both cation and anion lefts there lattice site and moves out of crystal and left a vacancy there. This is Schottky Defect. 8

9. NaCl is an example of Schottky Defect where both Na+ and Cl - left the crystal. 9

10. Some other consequences of Frankel and schottky defects 10

11. Main Differences Between Schottky Defect and Frankel Defect 11 Schottky Defect Frankel Defect It is due to equal number of cations and anions missing from lattice site. It is due to missing of ion from lattice site and occupies the interstitial site. This results in decrease of density of the crystal. This has no effect on density. This type of defect is found in highly ionic compounds with high coordination number. This type of defect is found in crystals with low coordination number. For Example:- NaCl , CsCl etc. For example:- AgCl , AgBr etc.