The correct statement(s) regarding defects in solids is/are:a)Frenkel defect is usually favoured by a very small difference in the sizes of cation and anion.b)Frenkel defect is a dislocation defect.c)Trapping of an electron in the lattice leads to the formation of F-centerre.d)Schottky defects have no effect on the physical properties of solids.Correct answer is option 'B,C'. Can you explain this answer?

Question

Answer

Explanation:

Frenkel Defect:
- Frenkel defect is usually favored by a very small difference in the sizes of cation and anion.
- It occurs when an ion is displaced from its normal lattice site to an interstitial site.
- This defect does not involve creation of new vacancies or interstitials.

Trapping of Electrons:
- Trapping of an electron in the lattice leads to the formation of F-center.
- F-centers are color centers that give color to many solids.
- This type of defect can significantly affect the optical properties of solids.

Schottky Defects:
- Schottky defects involve the creation of equal numbers of cation and anion vacancies to maintain charge neutrality.
- These defects affect the density of the material, which in turn can influence the physical properties like conductivity and diffusion rates.
- Contrary to the statement, Schottky defects do have an effect on the physical properties of solids.
In conclusion, the correct statement regarding defects in solids is that Frenkel defect is not a dislocation defect, rather it involves cation or anion displacement, and trapping of an electron in the lattice leads to the formation of F-center which can impact the optical properties of solids. Schottky defects do have effects on the physical properties of solids, unlike the statement suggests.

Answer

Schottky defect is a vacancy defect (due to missing ions) and also a stoichiometric defect, as the ratio of the number of cations and anions remains the same. (Schottky defects have an effect on the physical properties of solids). It occurs only when there is a small difference in size between cations and anions. This is produced as the result of the thermal incorporation of unoccupied lattice sites from the exterior of the crystal. The lattice undergoes thermal vibration and thermal expansion when the temperature is raised above 0 K. When it happens, the pair of vacancies is incorporated in the crystal.

A Frenkel defect, Frenkel pair or Frenkel disorder is a type of point defect in a crystal lattice. The defect forms when an atom or smaller ion (usually cation) leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location. In a Frenkel defect, an additional ion exists in the interstitial space within a crystal lattice. In Schottky defect, there is an empty space in a crystal lattice.

An F-centre, Farbe- entre or colour centre (from the original German 'Farbzentrum'; 'Farbe' means 'colour' and 'Zentrum' means 'centre') is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more unpaired electron. (Trapping of an electron in the lattice leads to the formation of F-centre).

Hence, options 2 and 3 are correct.

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