defects

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. This is 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 in the structure.