Multiple Choice

The correct statement(s) regarding defects in solids is(are):

AFrenkel defect is usually favoured by a very small difference in the sizes of cation and anion.
BFrenkel defect is a dislocation defect.
Correct Answer
CTrapping of an electron in the lattice leads to the formation of F-center
Correct Answer
DSchottky defects have no effect on the physical properties of solids.

Solution

Frenkel defect is a defect which is created when an ion leaves its appropriate site in the lattice and occupies an interstitial site. A hole or vacancy is thus produced in the lattice.
Frenkel defect is exhibited in ionic compounds in which the radius ratio is low. The cations and anions differ much in their sizes and the ions have low co-ordination numbers. Examples are ZnS, AgBr, AgI, AgCl.
The Schottky defect is a defect which is produced when one cation and anion are missing from their respective positions leaving behind a pair of holes. The crystal as a whole remains neutral because the number of missing positive ions (cations) and negative ions (anions) is the same.

Consequences of Schottky defect:
1. The density of the crystal decreases.
2. The crystal begins to conduct electricity to a small extent by the ionic mechanism.
3. The presence of too many voids lowers lattice energy or the stability of the crystal.
4. F-center: A colour centre consisting of an electron trapped by a negative ion vacancy in an ionic crystal such as an alkali halide or an alkaline-earth fluoride or oxide.

Hence, the correct options are $$\text{B}$$ and $$\text{C}$$.

SIMILAR QUESTIONS

Solid State

Due to Frenkel defect, the density of ionic solids :

Solid State

Which of the following statement(s) for crystals having Frenkel defect is/are correct?

Solid State

Which of the following is a correct statement regarding defects in crystalline solids?

Solid State

Which among the following solids shows Frenkel defect?

Solid State

Frenkel defects are not found in alkali metal halide. Why?

Solid State

Give the correct order of initials T (true) or F (False) for following statements: I. In an anti-fluorite structure, anions form FCC lattice and cations occupy all tetrahedral voids. II. If the radius of cations and anions are $$0.2\ \mathring A$$ and $$0.95\ \mathring A$$, then co-ordination number of cation in the crystal is $$4$$. III. An ion is transferred from a lattice site to an interstitial position in Frenkel defect. IV. Density of crystal always increases due to substitutional impurity defect.

Solid State

Density of a crystal decreases due to Schottky defect and remains constant due to Frankel defect. If true enter 1,else enter 0.

Solid State

Frenkel defect does not change the density of the ionic crystal whereas, Schottky defect lowers the density of ionic crystal. Give a reason.

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