Why is Frenkel defect defect not found in pure alkali metal halides?

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Frenkel defectarenot found in pure alkali metal halidesbecause due to larger size of the cations of thealkali metals, they cannot get into the interstitial sites,

Frenkel defect is not found in the pure alkali metal halides because this defect is due to vacancy of ion ,which is shifted in interstitial spaces,and pure alkyl halide do not have vacancy.