Hi Rahaman!

Schottky Defect is the defect which lowers the density of Crystals! Schottky Defect is a point defect which is caused by vacant positions. When oppositely charged ions leave their positions, vacancies are created. Hence the density becomes low. The surrounding atoms also move to occupy these vacancies!

Hope this is helpful!

All the best!

Hello aspirant

In ionic-solids VACANCY DEFECT lowers the density of the crystal. in this defect some of the lattice site are vacant, which results in decrease in density of crystal. this defect also develop when crystals are heated. in non ionic-solids SCHOTTKY DEFECT lowers the density of crystal.

hope this helps. All the best.