Defects in Crystals

In crystallography, defects are irregularities or deviations from perfect patterns in a crystal lattice. They can be classified into three types based on their dimensions – point defects, line defects, and surface defects.

Point Defects

Point defects are the simplest type of defect and occur when an atom is missing or is located at an incorrect site in the lattice. Point defects can be classified into two types:

1. Vacancy Defects: In a vacancy defect, an atom is missing from its lattice site, resulting in a vacant site.

2. Interstitial Defects: In an interstitial defect, an atom occupies a site that is not normally occupied.

Line Defects

Line defects are also known as dislocations and occur when there is a deviation from the normal stacking sequence of atoms in a crystal. They can be classified into two types:

1. Edge Dislocations: An edge dislocation occurs when an extra half-plane of atoms is introduced in a crystal.

2. Screw Dislocations: A screw dislocation occurs when the planes of atoms are spiraled around an axis.

Surface Defects

Surface defects occur at the boundary between two crystals, or between a crystal and its surroundings. They can be classified into two types:

1. Grain Boundaries: Grain boundaries occur when two grains with different crystal orientations meet.

2. Twin Boundaries: Twin boundaries occur when two regions of a crystal have the same orientation but are mirror images of each other.

Answer Explanation

The given question asks about the defect which occurs due to imperfect packing of atoms during crystallization. Such defects are usually point defects or line defects. Surface defects occur at the boundaries of two crystals and are not related to packing during crystallization. Therefore, the correct answer is option 'D' - none of these.