Question

Explain schottky and frenkel defects.

Answer 1

In a crystal substance sometimes the atoms or the constituent particles of the crystal show irregularities from the original arrangement which was ideal.
These defects can be categorized into impurity defect, stoichiometric defect or non-stoichiometric defects.

Complete answer:
Before defining or explaining about the terms we need to know some basic properties of crystals in general. Crystals are known to be imperfect. And solid constitutes a large number of small crystals. These small particles in the crystal show a number of defects in them. In case of the ionic solid crystals, the electrical neutrality is always maintained within the crystal, so instead of the interstitial or vacancy defects, the ionic crystals show frenkel and schottky defects.
At first we will consider the schottky defect, which is basically a vacancy defect shown by the ionic crystals. It is developed when equal numbers of anions and cations go missing inside the crystal. Since, the number of missing anions and cations are equal, the electrical neutrality is therefore maintained. This type of defect can be observed in compounds having higher coordination numbers.
Now if we consider the frenkel defect, it is a type of interstitial defect shown by the ionic lattices. It arises when the charge particle from one place moves to an interstitial site which is present in the same lattice structure. Since, the particle is only displaced from its original site and not removed from the crystal, the electrical neutrality is therefore maintained.

Note: The schottky defect is a type of point defect which results due the removal or missing of the same number of oppositely charged particles from the ionic crystal lattice.
Whereas, the frenkel defect is a type of point defect which arises when a charged particle leaves its original site and moves to an interstitial site in the same ionic crystal lattice.