PPT Slide
In pure metals, small numbers of vacancies are created by thermal excitation, and these are thermodynamically stable at temperatures greater than absolute zero.
At equilibrium, the fraction of lattices that are vacant (or vacancy concentration) at a given temperature is given approximately by the equation:
where n is the number of vacant sites in N sites and is the energy required to move an atom from the interior of a crystal to its surface. T is the absolute temperature.
The vacancy concentration in pure elements is very low at low temperatures.