The Solid State

lattice defect can be define as combination of Line defects and plane defects together are called lattice defects.

Frenkel Defect: This defect is shown by ionic solids. The smaller ion (usually cation) is dislocated from its normal site to an interstitial site . It creates a vacancy defect at its original site and an interstitial defect at its new location.
 Frenkel defect is shown by ionic substance in which there is a large difference in the size of ions so it is due to difference in size of Ag⁺ and CI^–, Ag⁺ occupies voids.

In hexagonal close packing octahedral void as well as tetrahedral void are produced.

The co-ordination number of an octahedral void  is  6 : 6.