Lattice dynamics in intermetallic Mg2Ge and Mg2Si

Area of Science:

• Materials Science
• Solid State Physics
• Thermodynamics

Background:

• Understanding lattice dynamics is crucial for thermoelectric materials.
• Polycrystalline Mg(2)Ge and Mg(2)Si are intermetallic compounds with potential applications.

Purpose of the Study:

• To compare the lattice dynamics of Mg(2)Ge and Mg(2)Si.
• To investigate the factors contributing to differences in their vibrational properties.

Main Methods:

• Combined experimental techniques: inelastic neutron scattering, calorimetry, and Raman scattering.
• Theoretical calculations: density functional theory.
• Microscopic and macroscopic measurements.

Main Results:

• Volume thermal expansion coefficients determined: 4.37(5)·10⁻⁵ K⁻¹ for Mg(2)Ge and 3.69(5)·10⁻⁵ K⁻¹ for Mg(2)Si.
• Phonon density of states from neutron scattering align with theoretical predictions.
• Macroscopic Grüneisen parameters estimated: γ(Mg(2)Si) = 1.17(5) and γ(Mg(2)Ge) = 1.46(5), consistent with Raman data.

Conclusions:

• Mg(2)Ge shows greater anharmonicity and thermal expansion compared to Mg(2)Si.
• Mass homology alone does not explain differences in vibrational states; elemental bonding plays a significant role.