Name: Radius Ratio and Coordination Number
Uploaded: 2019-07-19
Duration: 3 min 49 s
Description: The radius ratio plays a very important role in the determination of a structure in an ionic crystal. Watch the video to know more about the radius ratio of...

Question

What do you understand by point defects? Briefly explain the different types of point defects.

Accepted Answer

When the deviations exist in the regular or periodic arrangement of the constituent particles (atoms or ions) in the crystal, these defects are termed atomic imperfections or point defects.
These defects are caused by the following points.
When some of the constituent particles are missing from their normal positions, these unoccupied positions are termed holes or vacancies.
When some of the constituent particles are missing from their positions and these particles have shifted either to interstitial vacant sites or to positions which are meant for other particles.

Types of point defects: Point defects are classified into the following three types:
Defects in stoichiometric crystals: If imperfections in the crystal are such that the ratio between the cations and anions remains the same as represented by the molecular formula, i.e., stoichiometry of the solid is not disturbed, the defects are called stoichiometric defects. These are also called intrinsic defects or thermodynamic defects.

Defects in non-stoichiometric crystals : If, as a result of the imperfections in the crystal, the ratio of the cations to the anions becomes different from that indicated by the ideal chemical formula, the defects are called non-stoichiometric defects. The line defects are also called dislocations. The two main line defects are called edge dislocations and screw dislocations.

Impurity defects: These defects arise when foreign atoms are present at the lattice site in place of host atoms or at the vacant interstitial sites.

What do you understand by point defects? Briefly explain the different types of point defects.

Important Questions on States of Matter: Solid State

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