Question

Which of the following statement regarding crystal defects is /are not correct?

• A. Schottky defects are dislocation defects
• B. Three cationic vacancies are created per ion of $A{l}^{3+}$ inserted if NaCl crystals are doped with $A{l}^{3+}$ ion
• C. Addition of $As$ to $Si$ results in formation of n-type semiconductors
• D. Packing fraction remains unaffected in vacancy defect

Answer 1

Answer: (A), (B), (D)

The correct options are
A Schottky defects are dislocation defects
B Three cationic vacancies are created per ion of $A{l}^{3+}$ inserted if NaCl crystals are doped with $A{l}^{3+}$ ion
D Packing fraction remains unaffected in vacancy defect

(a) Schottky defects are formed due to missing of equal number of cations and anions from a crystal lattice. Frenkel defects are known as dislocation defects. Hence this statement is wrong.

(b) When $A{l}^{3+}$ is inserted in NaCl, two cation vacancies are created. After the insertion of $A{l}^{3+}$ in place of one $N{a}^{+}$, the crystal lattice has +2 charge. To maintain electroneutrality, two $N{a}^{+}$ ions must be removed and hence only two vacancies are created.

c) As has one more valence electron than Si, so addition of As to Si results in formation of n-type semiconductors.

d) Packing fraction is the fraction of volume occupied in a crystal structure. Hence, due to vacancy defect, packing fraction decreases.