On a change in the sign of the entropy of vacancy formation in a crystal

The entropy of vacancy formation (s _v) in a crystal increases with the temperature and, at a certain critical temperature, changes its sign from negative to positive. Physical reasons for this change are considered and a condition under which s _v is positive is established. During the melting of metals, s _v is positive and the appearance of vacancies leads to disordering of the crystal, rendering it less stable and facilitating the formation of new vacancies.