Local lattice potentials and steady-state vacancies in ionic crystals
  Basing on peculiarities of local potentials, the two principal trends in vacancy formation are revealed. The proximity to the threshold of local ionic stability due to a giant potential contribution of electronic delocalization accounts for thermal anion vacancies typical of intrinsic semiconductors of AB type. On the other hand, the tendency towards equalizing the potential field results in a high concentration of structural cation vacancies observed in Ni_3 Sb and relative compounds. 
Eugene V. Kholopov