|—n , pl -cies|
|1.||the state or condition of being vacant or unoccupied; emptiness|
|2.||an unoccupied post or office: we have a vacancy in the accounts department|
|3.||an unoccupied room in a boarding house, hotel, etc: put the "No Vacancies" sign in the window|
|4.||lack of thought or intelligent awareness; inanity: an expression of vacancy on one's face|
|5.||physics a defect in a crystalline solid caused by the absence of an atom, ion, or molecule from its position in the crystal lattice|
|6.||obsolete idleness or a period spent in idleness|
in crystallography, absence of an atom or molecule from a point that it would normally occupy in a crystal. Such an imperfection (crystal defect) in the regular spacing of atoms changes the electrical and optical properties of the crystal. Colour centres are vacancies that give colour to many solids. Vacancies can be created by mechanical deformation of the crystal, rapid cooling from high temperature, or the impact of radiation on the crystal. In the so-called Schottky defect, an atom moves from the inside of the crystal to its surface, leaving behind an isolated vacancy. In the Frenkel defect, an atom moves to a new position between other atoms of the solid. The empty space created by the migration of the atom is a vacancy. The relative numbers of these two types of defects vary from crystal to crystal. See also colour centre.
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