Difference Between Point Defect and Line Defect

The key difference between point defect and line defect is that the point defects occur only at or around a certain point of the crystal lattice whereas the line defects occur in a plane of atoms in the middle of the crystal lattice.

Crystallographic defects are the imperfections of the repeating pattern of a crystal lattice. These defects interrupt the regular pattern of the lattice. There are several types of crystallographic defects such as point defects, line defects, planar defects and bulk defects. It is easy to visualise a point defect, but the visualization of a line defect is difficult.

CONTENTS

1. Overview and Key Difference
2. What is Point Defect
3. What is Line Defect
4. Side by Side Comparison – Point Defect vs Line Defect in Tabular Form
5. Summary

What is Point Defect?

Point defects are irregularities that occur at or around a single point of the crystal lattice. Typically, this type of defect forms either due to the presence of extra atoms or due to the loss of atoms from the lattice. Therefore, these defects are considerably small. However, sometimes there are some larger defects as well. We call them dislocation loops.

Several forms of point defects can occur in a crystal lattice.

• Vacancy defects
• Interstitial defects
• Frenkel defects
• Substitutional defects
• Schottky defect

What is Line Defect?

Line defects are a form of crystallographic defects in which the defects occur in a plane of atoms in the middle of the crystal lattice. Therefore, these are linear defects. There the atoms of the lattice are misaligned. The two major forms of these defects are;

• Edge dislocation
• Screw dislocation

Sometimes we can see a combined effect of both these defects. We call it a mixed dislocation. Edge dislocations occur due to the loss of a plane of atoms in the middle of the crystal. In these dislocations, the adjacent planes of atoms become not straight; bend around the missing plane to make the crystal structure well-ordered on either side.

A screw dislocation is difficult to envision. There, the planes of atoms in the crystal trace a helical path around the dislocation line.

What is the Difference Between Point Defect and Line Defect?

Point defects are irregularities that occur at or around a single point of the crystal lattice. These defects form either due to an extra atom or due to the loss of atom. In addition, it is easy to visualize a point defect. Line defects are a form of crystallographic defects in which the defects occur in a plane of atoms in the middle of the crystal lattice. These defects occur when a plane of atoms misalign. Moreover, it is difficult to visualize a line defect. This is the main difference between point defect and line defect.

Summary – Point Defect vs Line Defect

Crystallographic defects are the imperfections in crystal lattices. The difference between point defect and line defect is that the point defects occur only at or around a certain point of the crystal lattice whereas the line defects occur in a plane of atoms in the middle of the crystal lattice.

Reference:

1. “Crystallographic Defect.” Wikipedia, Wikimedia Foundation, 10 June 2018. Available here  
2. “Crystal Defects.” Mannich Reaction | Mannich Reaction Mechanism | Chemistry@TutorVista.com. Available here  

Image Courtesy:

1.’Point defects in crystal structures’By DaniFeri – Own work, (CC BY-SA 3.0) via Commons Wikimedia  
2.’Dislocation edge d2’By Wikityke (CC BY-SA 2.5) via Commons Wikimedia