Vacancies in magnesium silicide – stoichiometric vacancies preferred?

Abstract

Magnesium silicide (Mg2Si) in its calcium fluorite (CaF2) structure is a hardly investigated material up to now. However, it may play an important role in upcoming new materials for photovoltaic applications due to its semiconducting properties and the fact that it is consisting of non‐poisonous elements. On the other hand metastable phases of Mg2Si play an extremely important role in the hardening of 6xxx (AlMgSi‐based) aluminum alloys. Hence, it seems worth investigating the formation energy of vacancies in Mg2Si. In this paper we calculate the formation energy for vacancies on the different sublattices using the ab‐initio method SIESTA. While the values for the silicon (1.04 eV) and the magnesium vacancy (1.74 eV) lie in the expected range, the formation energy of the di‐vacancy and the stoichiometic tri‐vacancy turn out to be just 0.68 eV and 0.78 eV, respectively. This is smaller than the value for both mono‐vacancies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Lattice stability and formation energies of intrinsic defects in Mg2Si and Mg2Ge via first principles simulations

“…Concerning Mg 2 Si, the formation energy was found to be about -0.173 to -0.189 eV/at. (if we except the Staab's results [14]), whereas it is about -0.236 to -0.254 eV/at.…”

“…recently results concerning the formation energy became available [10][11][12][13][14][15], especially for Mg 2 Ge [10,12,13]. Concerning Mg 2 Si, the formation energy was found to be about -0.173 to -0.189 eV/at.…”

“…Mg 2 Si is an n-type semiconductor with an indirect band gap of 0.66-0.78 eV while Mg 2 Ge is a semiconductor with a slightly smaller indirect band gap of 0.57-0.74 eV [5]. Despite the numerous studies dedicated to Mg 2 Si, some discrepancies between experimental and simulation results exist especially concerning the existence or not of several different high pressure phases [6][7][8][9] and the formation enthalpies of both the pure compound [10][11][12][13][14][15] and the intrinsic defects (vacancies, antisites) [14][15].…”

(Meta-)stable phases and pre-Guinier-Preston zones in AlCu alloys constructed from ab initio relaxed atomic positions - Comparison to experimental methods

“…(1) rewritten for a compound by Zhang and Northrup 35 is not sufficient, since this was done for a 1:1 compound like GaAs. However, the formulation for a 2:1 compound was recently published by Staab 36 for Mg 2 Si – here written for Al 2 Cu: where E D (corresponding to $E_{{\rm tot}}^{N - 1} $ in Eq. (1)) is the total energy of the supercell containing vacancies.…”

Significant Roles of Intrinsic Point Defects in Mg2X (X = Si, Ge, Sn) Thermoelectric Materials

“…Both Mg interstitials and Mg vacancies possibly exist in Mg 2 Si system based on experimental results . The formation energies of intrinsic defects in Mg 2 Si and Mg 2 Ge compounds have been theoretically studied . Kato et al studied the intrinsic defects in Mg 2 Si by dual‐space Gaussian pseudopotentials (norm conserving) and an exchange–correlation (XC) functional (local‐density approximation) .…”