What are the consequences of Schottky defects ?

Explanation

1. Schottky defect. In a crystalline solid of type AB. This type of defect is produced when equal number of positive ions and negative ions are missing from their respective positions. Since the number of missing positive ions is equal to the number of missing negative ions the crystal as a whole is electrically neutral. This defect is more common in ionic compounds with high coordination number and where the ions (positive and negative) are of similar size. For example, NaCl, KCl, CsCl and KBr.

Consequences of Schottky defect.
(i) As ions are missing from their lattice sites, presence of large number of Schottky defect lowers the densiy of the crystal.
(ii) Ionic conductivity and diffusion in solid state in stoichiometric solids to the presence of lattice vacancies.
2. Frenkel defect. This type of defect arises when an ion is missing from its normal lattice site and occupies an interstitial site. This defect is more common in ionic compounds in which there is a large difference in sizes between positive and negative ions e.g. ZnS, AgCl, AgBr and Agl.
Consequences of Frenkel defect.
(i) There is no decrease in density when Frenkel defect alone is present as the missing ion is present at an interstitial site in the crystal.
(ii) In decreases the dielectric constant of solids.
(iii) Compounds with Frenkel defect show ionic conductivity and diffusion in solid sate due to presence of lattice vacancies.