Crystal Defects
- Which point defect in crystals does not change the density of the solids and why?
Ans. A Frenkel defect. This defect does not change the density of the solid due to the migration of the ions
within the crystal, which does not change the volume or the mass.
within the crystal, which does not change the volume or the mass.
- Which point defect increases the density of the solids?
Ans. When some constituent particles occupy an interstitial site, the crystal is said to have interstitial
defect. This point defect increases the density of the substance.
defect. This point defect increases the density of the substance.
- What type of defects arise in a solid when it is heated?
Ans. When a solid is heated, vacancy defect can arise. A solid crystal is said to have vacancy defect
when some of the lattice sites are vacant. Vacancy defect leads to a decrease in the density of the
solid.
when some of the lattice sites are vacant. Vacancy defect leads to a decrease in the density of the
solid.
- Which defect causes a decrease in the density of crystals?
Ans. Schottky defect.
- What is the cause of the Frenkel defect in solids?
Ans. 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.
creating a vacancy, and becomes an interstitial by lodging in a nearby location.
- Describe the main feature of Schottky defect in solids?
Ans. In ionic crystals, this type of point defect forms when oppositely charged ions leave their lattice
sites, creating vacancies.
sites, creating vacancies.
- When do we observe Schottky defects in solids?
Ans. Schottky defect is observed when equal number of cations and anions are missing from the
lattice. This defect changes the density as a pair of ions are missing from the lattice.
lattice. This defect changes the density as a pair of ions are missing from the lattice.
- Write the example of solid which possess Frenkel defect?
Ans. Examples are AgBr, ZnS, AgCl, and AgI. Here the defect occurs mainly due to the smaller size
of Zn2+ and Ag+ ions.
of Zn2+ and Ag+ ions.
- Write the examples of solids which possess Schottky defects?
Ans. Sodium Chloride (NaCl), Potassium Chloride (KCl), Potassium Bromide (KBr), Caesium
Chloride (CsCl) and Silver Bromide (AgBr).
Chloride (CsCl) and Silver Bromide (AgBr).
- What are the various types of point defects?
Ans. There are three major types of point defect:
- Vacancies defect
- Interstitials and,
- Impurities defect
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