Which defect causes decreases in the density of crystal?

Which defect cause decrease in the density of crystal?

Even crystals prepared with great care contains certain irregularities called crystal defects. Which stoichiometric defects causes decrease in density of the crystal .

Which defect causes decrease in density of an ionic crystal, Schottky defect or Frenkel defect?

Which point defect decreases the density of crystals ?

Which stoichiometric defect decreases the density of the crystal?