It was noted that magnesium silicide with its calcium fluorite structure had hardly been investigated. However, metastable phases of Mg2Si played an important role in the hardening of 6xxx (AlMgSi-) alloys, and this made it worthwhile to investigate the formation energy of vacancies in Mg2Si. Here, the formation energy of vacancies on various sub-lattices was calculated by using an ab initio method. While the values for the silicon (1.04eV) and magnesium vacancy (1.74eV) were within the expected range, the formation energy of the di-vacancy and the stoichiometic tri-vacancy were only 0.68 and 0.78eV, respectively. This was smaller than the value for either monovacancy.

Vacancies in Magnesium Silicide - Stoichiometric Vacancies Preferred? T.E.M.Staab: Physica Status Solidi B, 2009, 246[7], 1587-9