Tag: imperfections in solids

Questions Related to imperfections in solids

Give the correct order of initials T(true) or F(False) for following statements:
I. In an anti-fluorite structure, anions form FCC and cations occupy all the tetrahedral voids
II. If the radius of cation and anion is $20$ and $95$ pm, then the coordination number of the cation is the crystal is $4$.
III. An atom or ion is transferred from a lattice site to an interstitial position in Frenkel defect.
IV. The density of crystal always increases due to substitutional impurity defect.

imperfections in solids solid state the solid state chemistry

  1. TTTT

  2. FFFF

  3. FFTT

  4. TFTF

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Correct Option: D

Which of the following defects in the crystals may lower the density?

imperfections in solids solid state the solid state chemistry

  1. Interstitial defect

  2. Vacancy defect

  3. Schottky defect

  4. Impurity defect

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Correct Option: B,C

Which kind of defect is introduced by doping in silicon crystal?

imperfections in solids solid state the solid state chemistry

  1. Dislocation defect

  2. Schottky defect

  3. Frenkel defect

  4. Electronic defect

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Correct Option: D

Which of the following may have Frenkel defect?

imperfections in solids solid state the solid state chemistry

  1. Sodium chloride

  2. Zinc sulphate

  3. Silver bromide

  4. Diamond

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Correct Option: B,C

Which of the following statement(s) is/are incorrect regarding the defects in solids?

imperfections in solids solid state the solid state chemistry

  1. $AgBr$ crystal show both Schottky and Frenkel defect

  2. Impurity defect by doping of Arsenic in Silicon results n-type semiconductor

  3. Doping in crystal introduces dislocation defect

  4. Metal deficient defect can occur with extra anion present in the interstitial voids

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Correct Option: C,D

The correct statement(s) regarding defects in solid is (are)

imperfections in solids solid state the solid state chemistry

  1. Frenkel defect usually favoured by a very small difference in the sizes of cation and anion

  2. Frenkel defect is a dislocation defect

  3. Trapping of an electron in the lattice leads to the formation of F-centre

  4. Schottky defect have no effect on the physical properties of solids

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Correct Option: B,C

Missing of one cation and one anion from the crystal lattice is called

imperfections in solids solid state the solid state chemistry

  1. ionic defect

  2. crystal defect

  3. schottky defect

  4. frenkel defect

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Correct Option: C
Explanation:

Schottky defect arises due to a vacancies at cation sites and equal number of vacancies at anion sites.

Hence, option C is correct.

In a crystal, pair of ions are missing from normal sites. This is an example of which defect?

imperfections in solids solid state the solid state chemistry

  1. Extended defect

  2. Interstitial defect

  3. Frenkel defect

  4. Schottky defect

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Correct Option: D
Explanation:

Schottky defect arises due to a vacancies at cation sites and equal number of vacancies at anion sites.

Which of the following crystals does not exhibit Frenkel defect?       

imperfections in solids solid state the solid state chemistry

  1. $AgBr$

  2. $AgCl$

  3. $KBr$

  4. $ZnS$

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Correct Option: C
Explanation:

Condition for Frankel defects in an ionic crystal is-

  1. The size difference between the ions should be large.
  2. Smaller ion (cation) move to interstitial site.

Frenkel defect generally appears in ZnS, AgBr, AgI, AgCl etc.
Alkali metal shows Schottky defect. Here KBr exhibits Schottky defect. However, it does not show Frankel defect. ZnS has a large size difference between the ions.

Option C is correct.

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

imperfections in solids solid state the solid state chemistry

  1. Frenkel defect is usually favoured by a very small difference in the sizes of cation and anion.

  2. Frenkel defect is a dislocation defect.

  3. Trapping of an electron in the lattice leads to the formation of F-center

  4. Schottky defects have no effect on the physical properties of solids.

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Correct Option: B,C
Explanation:

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 $\text{C}$.