First-principles studies of lattice dynamics and thermal properties of Mg₂Si_1-xSn_x

We present the results of a mixed-space approach, based on first-principles calculations, to investigate phonon dispersions and thermal properties of Mg₂Si and Mg₂Sn, including the bulk modulus, Grüneisen parameter, heat capacity, and Debye temperature. It is shown that good agreements are obtained between the calculated results and available experimental data for both phonon dispersions and thermal properties. The phonon dispersions are accurately calculated compared with experimental data due to the high-quality description of LO-TO splitting and transverse acoustic branches along the Γ-K-X symmetry line. We also calculate the heat capacity C P and Debye temperature of Mg₂Si_1-xSn x alloys (x = 0.375, 0.5, 0.625, 0.875). The C P values at high temperature range from 0.5 to 0.7 J/g/K and ΘD values at room temperature from 332 to 384 K as the Sn content decreases from 0.875 to 0.375.