A common type of point defect that occurs in a crystal of zinc sulphide is a vacancy defect. In this defect, an atom is missing from its lattice position, creating a gap or a vacancy in the crystal structure.

An ionic defect involves the migration of the ions within a crystal. It can affect the density and volume of the crystals.

1).schottky defect arises due to departue of ions (both cation and anion in equal ratio) from crystal lattice leaving holes that favour conductivity. The equal no of ions depart because to maintain the electrical neutrality of crystal. It was discovered by walter.H schottky in 1930.

But in frenkel defect ions(cations) are missing from there normal lattice site and occupying an interstitial site between the lattice points. They dont depart from crystal lattice. Because no departure occure so crystal remain electrically neutral. It was discovered by Yakov frenkel in 1926.

2) schottky defect is only vacancy defect but frenkel defect is vacancy as well as interstitial defect.

3). Schottky defect decreases density and strength of the crystal. But frenkel defect doesnt affect density.

4).schottky defect is shown by the ionic solids having high coordination no and approx. same size of cation and anion(i.e r+ve/r-ve approaches to 1)

While frenkel defect is shown by the compound having low coordination no and size of anion larger than cation(i.e r+ve/r-ve approches the minimum value).

By

Sandeep Singh Lingwal

Srinagar, Uttrakhand

In the frenkel defect the ions are not removed from the crystal.so there will be no change in the crystal structure. that is there is no decrease in the no of ions.all the ions are inside the crystal.they are only dislocated.

Within a crystal there are point defects and line defects; point defects are missing or extra lattice points within the crystal lattice (vacancies or interstitials), line defects may be due to an 'extra' half lattice plane within the crystal. The end of a line defect plane is known as an edge dislocation, screw dislocations occur where part of a crystal is displaced over one lattice direction and is therefore twisted. Dislocation loops can occur where an edge and a screw dislocation intersect.