Name: The Face-centered Cubic Unit Cell
Uploaded: 2019-07-19
Duration: 5 min 6 s
Description: The video discusses the parameters involved in defining a Face centered cubic unit cell. It describes the relationship between the edge length of the cube an...

Question

Explain interstitial defects and impurity defects.

Accepted Answer

Interstitial defects:

When cation or anion from ionic solid leaves its regular site and moves to occupy a place between the lattice site called interstitial position, the defect is called interstitial defect or Frenkel defect.

Due to this defect, the density of the substance is not affected.

Ionic compounds with large difference in the size of the cation and anion show interstitial defect.

Silver halides and $ZnS$ show interstitial defect. The cations ${Ag}^{+}$ and ${Zn}^{2 +}$ occupy the interstitial space as they have relatively smaller size.

Impurity defects:

The impurity defect occurs when a regular cation of the crystal is replaced by some different cation.

If the impurity cation is substituted in place of regular cation, it is called substitution impurity defect.

If the impurity is present in the interstitial positions, it is called interstitial impurity defect.

When one metal is substituted by another metal, substitution alloy is formed. Example- When copper metal is substituted by zinc metal in $3 : 1$ ratio, brass is obtained.

The impurity defect completely changes the original properties of crystalline solid. Example- Iron is soft, malleable and ductile. Carbon is introduced as impurity to form stainless steel. It is an interstitial alloy and is hard, stronger, less ductile, shiny and has bright appearance.

Explain interstitial defects and impurity defects.

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