Why AgBr shows both Schottky and Frenkel defects??

AgBr shows both Frenkel and Schottky defects because the radius ratio for AgBr is intermediate.

Explaination:

Ions have Schottky defects when their anions and cations are both absent from the crystal lattice.

In AgBr, the Ag⁺ ions and corresponding Br^̶̶‒ ions are absent from the crystal lattice causing Schottky defects.

However, Ag⁺ ions are exceptionally mobile and they have a tendency to move about inside the lattice. So they complement the Schottky defects with Frenkel defects with the Ag⁺ ions trapped in interstitial spaces. Because of the similar size of Ag⁺ ions and Br^‒ ions and the small size of Ag⁺ ions and the fact that Ag⁺ ions have a property to be mobile, both Schottky and Frenkel defects occur.