Lattice dynamics of Mg-Sc lightweight shape memory alloys

Lattice vibrations play a significant role in the martensitic phase transformation of MgSc alloys, thus in the shape memory effects as well. In this article, the phonon spectra and thermodynamic properties of MgSc alloys with different structures were systemically studied by first-principles methods. The phonon spectra of Mg-18.75 at.%Sc and Mg-20.83 at.%Sc in austenite phase are fundamentally different, and the experimental martensitic transition behavior of MgSc alloys with different compositions can be well explained by the lattice dynamics. The occurred Fermi surface nesting at specific compositions leads to the appearance of phonon imaginary frequency, thus resulting in the lattice instability. The entropy change and latent heat obtained from harmonic phonon calculations suggests that the MgSc alloys are promising for the application in low-temperature elastocaloric cooling, and that the entropy changes are comparable to the well known cooling materials such as BaTiO3 and NiTi.