The vibrational and thermal properties of Mg₂Si: Anharmonic effects

Magnesium silicide is an efficient thermoelectric material with many other technological and industrial applications. Understanding its thermal properties is crucial, yet these fundamental properties remain insufficiently explored both experimentally and theoretically. This work presents the results of a thorough first-principles study of the temperature (T)-dependence of phonon frequencies and thermal properties of Mg₂Si. The anharmonic T-dependence of phonon frequencies has been computed, for the first time, using two advanced approaches (temperature dependent effective potential and ab-initio determination of anharmonic phonon peaks). The calculated results are discussed in comparison with each other and with the available experimental data obtained by Raman spectroscopy. A method for enhancing the agreement between calculated and experimental data is proposed. Using a recently developed approach that greatly extends the validity range of the quasi-harmonic approximation, accurate predictions of the thermal properties (namely, thermal expansion, specific heat, and isothermal bulk modulus) of Mg₂Si are provided.