Defects in Crystalline Materials

Nov 22 • Notes, Science Notes • 12276 Views • 3 Comments on Defects in Crystalline Materials

A perfect crystal, with every atom of the same type in the correct position, does not exist. Defects contributes to the change in the properties of the materials. There may exist several types of crystalline defects in materials. This post includes Chemistry notes on Defects in Crystalline Materials explaining various crystalline defects such as Point Defects, Stacking Faults, Stoichiometric  defects and Non-Stoichiometric Defects that generally occur in solid state. If you are interested you can refer our Science Note Section for further related searches. Now lets discuss Defects in Crystalline Materials in detail.

Defects in Crystalline Materials

Generally there defect in crystalline materials are classified into following categories:

1. Point Defects
2. Stoichiometric  defects
3. Non-Stoichiometric  Defects
4. Stacking Faults

1. Point Defects: All the atoms present in a perfect lattice are at specific at a proper atomic site. A pure metal generally consists of two types of point defects that are

Point Defect

• Vacancies: These are vacant atomic sites in a structure which arises due to plastic deformation and  high energy particle irradiation in a material.
• Interstitial point defects: These are extra atoms positioned between atomic sites.

2. Stoichiometric  Defects: These defects includes dislocation of equal amount of cation and anion from a crystalline. These are also further described which are as follows:

• Schottky Defect: In order to conserve overall neutral charge, vacancy must be occurred either in pairs of opposite sign forming die. These vacancies are termed as Schottky defects.
• Frankel Defect: In order to conserve overall neutral charge, vacancy must be occurred either in pairs of same sign forming die. These vacancies are termed as Frankel defects.

Example: AgBr is the compound which show both Schottky and Frankel defect.

3. Non-Stoichiometric  Defects: These defects includes dislocation of unequal amount of cation and anion from a crystal.These defects are further classified as

• Availability of extra anion: A compound may have excess metal ion if a negative ion is absent from its lattice site leaving a hole which is occupied by electron to maintain neutrality.
• Availability of extra cation: A may have metal deficiency due to the absence of a metal from its lattice site. The charge is balanced by an adjacent ion having higher positive charge.

4. Stacking Faults: Stacking fault is a kind of planner defect that is generally formed when regular sequence of stacking are disturbed over the region. Stacking faults are not observable in the plane where the stacking geometry is ABABAB because there does not exist any alternative site for layer “A” other than resting on the layer “B” and vice versa. These defects are further classified as

• Intrinsic stacking faults: In this case removal of a layer from the arranged sequence is done. For example, the sequence layer CBACBA is changed to CBABAC. Interchange of layer B and layer C is observed.
• Extrinsic stacking faults: In this case addition of a layer is done to the arranged sequence. For example, the sequence layer BACBAC is changed to BACABAC. Addition of layer A is done.

Follow: Defects in Crystalline Materials for pdf

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