Thermodynamic stability of Al/MgZn2 interfaces including vibrational entropy and thermal expansion contributions

The surface energies of Al(111) and MgZn 2 (0001) slabs, as well as the interface energies of the Al(111)||MgZn 2 (0001) interfaces with different terminations and stacking orders were calculated using a combination of first-principles and phonon calculations under the assumptions of the harmonic and quasi-harmonic approximations. The thermodynamic stabilities of slabs and interfaces at 0 K and finite temperatures were analyzed by considering the effects of vibrational entropy and volume. It is found that the surface energies decreased with temperature as a result of vibrational entropy and thermal expansion, which led to an additional -but limited- reduction on the free energy that did not change the thermodynamic stability of the surface slabs. The interface energy of the interfaces also decreased with temperature due to the vibrational entropy, while thermal expansion provided an additional positive or negative contribution to the interface energy. As a result, the thermodynamic stability of the interfaces changed depending on whether thermal expansion was considered. The effect of bond stiffness and thermal expansion on the surface and interface energies was discussed. This investigation provides a clear strategy to assess the effect of temperature and volumetric changes on the thermodynamic properties of surfaces and interfaces.