Q59 / 180 · COMEDK 2023 (Morning Shift) · Chemistry
Which defect leads to decrease in the density of crystal?
- AF-centre
- BFrenkel
- Correct answerCSchottky
- DInterstitial
Solution
In a Schottky defect, an equal number of cations and anions are missing from their lattice sites. This creates vacancies in the crystal structure.
Since the number of ions decreases while the volume of the crystal remains effectively constant, the total mass of the crystal decreases.
Density is defined as $\rho = \dfrac{Z \times M}{N_A \times a^3}$. As the mass of the unit cell decreases due to the missing ions, the density of the crystal decreases.
Frenkel defect involves ions moving to interstitial sites, which does not change the density. Interstitial defects involve extra atoms occupying interstitial sites, which increases density. F-centre is a type of non-stoichiometric defect related to trapped electrons, which does not cause a decrease in density.
Answer: Schottky
Since the number of ions decreases while the volume of the crystal remains effectively constant, the total mass of the crystal decreases.
Density is defined as $\rho = \dfrac{Z \times M}{N_A \times a^3}$. As the mass of the unit cell decreases due to the missing ions, the density of the crystal decreases.
Frenkel defect involves ions moving to interstitial sites, which does not change the density. Interstitial defects involve extra atoms occupying interstitial sites, which increases density. F-centre is a type of non-stoichiometric defect related to trapped electrons, which does not cause a decrease in density.
Answer: Schottky
Hence, the correct answer is option: 'C'.