Which stoichiometric defect increases the density of a solid?

Schottky defect : The absence of a cation or an anion from the position which it is expected to occupy in the periodic arrangement of ions since the solid with a Schottky defect contains lesser ions as compared to perfect crystal. The density of crystal exhibiting Schottky defect will be less as compared to that of perfect crystal. No stoichiometric defect increases the density of a solid. Interstitial defects, where extra atoms are squeezed into the crystal lattice, might increase the mass, but the volume also increases, usually resulting in a net decrease in density. Similarly, Frenkel defects (where an ion moves to an interstitial site, leaving a vacancy) will not increase density.