why does AgBr show both Scottky and Frenkel effect???

Dear student,
It is known that schottky defects arise due to missing of ions from their lattice point and Frenkel defects arise when the missing ions occupy the interstitial sites.
Now for the case of AgBr, we know that the radius of AgBr being intermediate, hence it shows both Frenkel and Schottky defects.
The major defect that occurs in AgBr is the Frenkel defect. It has ccp lattice, where atoms of Br occupies all octahedral holes along with the atoms of Ag. Ag moves from octahedral to tetrahedral sites thereby causing only cations to precipitate.
Also, Schottky defect in AgBr is exhibited due to precipitation of both cations and anions. Finally, the Ag+ ion is small in size in AgBr and therefore when removed from lattice point they can occupy interstitial sites and hence show both Frenkel and Schottky defects.
Regards
Sumit