Which of the following statement regarding defects in solids is/are correct?

Options

A. Frenkel defect is usually favoured by a very small difference in the sizes of cation and anion.
B. Frenkel defect is a dislocation defect.
C. Trapping of an electron in the lattice leads to the formation of `F`-centre.
D. Schottky defects have no effect on the physical properties of solids.

Answer

B, C

Explanation

In Frekel defect, certain ions, mostly cations, are missing from their lattice points and are present in the interstitial spaces. (Cations due to smaller size have more chances of slipping.) Stoichimetry is maintained.
In metal excess defects caused by anion vacancies, one or more anions are missing from the lattice points which are occupied by electrons.
In metal excess defects caused by anion vacancies, one or more anons are missing from the lattice points which are occupied by electrons.
The overall electrical neutrically is maintained. When `NaCl` crystal is heated with `Na` vapours, this kind of defect is observed.
The electrons impart colour to the crystal (yellow colour to `NaCl`). These are known as `F`-centres (Farbe's centres).