Question

What are stoichiometric defects or intrinsic defects in ionic crystals?

Answer 1

Hint: In stoichiometric defects, the ratio of positive and negative ions (Stoichiometry) and electrical neutrality of a solid is not disturbed. The compounds in which the number of positive and negative ions are exactly in the ratios depicted by their chemical formulae are called stoichiometric compounds. Sometimes they are also known as intrinsic or thermodynamic defects.

Complete answer:
Stoichiometric defects are intrinsic defects in which the ratio of cations to anions remains exactly the same as represented by the molecular formula.
They are mainly of two types:
Vacancy defects in which an atom is not present at its lattice sites causing that lattice site to be vacant and create a vacancy defect. Due to this defect, the density of a substance will decrease.
Interstitial defect is a defect in which an atom or molecule occupies the intermolecular spaces or interstitial sites in crystals. In this defect. Because of this defect the density of the substance increases.
Stoichiometric defects are also called intrinsic defects because they are due to the deviation from regular arrangement of atoms or ions in a crystal system and no external substance is being added to the system in this type of defects.

Note:
In ionic solids interstitial defects and vacancy defects are known as Frenkel and Schottky defect respectively. Frenkel defect happens when there is a huge difference in the size of anion and cation in the crystal. E.g. \[AgCl\] . Schottky defect occurs mostly when the size of cations and anions of the compound are almost the same. E.g. \[NaCl\] .