Which is more likely to form in a metal a Frenkel defect or

Which is more likely to form in a metal, a Frenkel defect or a Schottky defect? Justify answer.

Solution

Schottky defect :-

It is basically a vacancy defect in ionic solids. In order to maintain electrical neutrality, the number of missing cations and anions are equal. Like simple vacancy defect, Schottky defect also decreases the density of the substance. Number of such defects in ionic solids is quite significant

Frenkel defect :-

This defect is shown by ionic solids. In this defect the smaller ions are dislocated from its normal site
to an interstitial site . It generate a vacancy defect at its original site and an interstitial defect at
its new location. Frenkel defect is also called dislocation defect

In this type of defect, density remains same. Frenkel defect is shown by ionic substance in which
there is a large difference in the size of ions, for example, ZnS, AgCl, AgBr and AgI shows this effect
due to small size of Zn2+ and Ag+ ions.

For example, in NaCl there are approximately 106 Schottky pairs per cm3 at room temperature. In 1
cm3 there are about 1022 ions. Thus, there is one Schottky defect per 1016 ions. Schottky defect is
shown by ionic substances in which the cation and anion are of almost similar sizes. For example,
NaCl, KCl, CsCl and AgBr. It may be noted that AgBr shows both, Frenkel as well as Schottky
defects

But in case of metals, Typical metallic structure doesn\'t seem to have a defect as such Yet, metal ions may migrate to interstitial voids, this defect is called Frenkel defect. By reaction with a non-metal on the surface, metals may liberate electrons e.g. Zinc, this defect is called Metal Excess defect due to anionic deficiency.

Hence FRENKEL defect is more likely to form in a metal