Pressure Coefficient of the Band Gap in Mg2Si, Mg2Ge, and Mg2Sn

The pressure deri vative of the band gap, (∂E/∂P)T, has been determined to be + 3 × 10−6 e Vbar−1 for Mg2Sn by measurements of the pressure derivative of the electrical conductivity. Similar measurements on Mg2Si and Mg2Ge were inconclusive, but estimates of this parameter were made from the shift of the optical obsorption edge with pressure. (∂E/∂P)T = (0 ± 0.5) × 10−6 e Vbar−1 for both compounds. The similarity of the coefficients for Mg2Si and Mg2Ge suggests that the symmetries of the band edges of both compounds are similar, while either the conduction band edge, the valence band edge, or both edges in Mg2Sn may have a different symmetry.