Tunable piezoelectric and ferroelectric responses of Al 1− x Sc x N: The role of atomic arrangement

In this study, we present first-principles investigations of the atomic structure of Al 1− x Sc x N and its influence on its piezoelectric and ferroelectric properties. The unbiased structure searching revealed that Al 1− x Sc x N with phase separation feature, where AlN and ScN form a layered structure with different symmetries, is more stable than the corresponding wurtzite structure. The piezoelectric response of Al 1− x Sc x N is strongly dependent on the atomic arrangements; in particular, Al 0.5 Sc 0.5 N with a wurtzite structure exhibits a large positive e 33 of 4.79 C/m 2 , whereas Al 0.5 Sc 0.5 N with a phase separation structure exhibits a negative e 33 of −0.67 C/m 2 . Moreover, the ferroelectric switching of Al 1− x Sc x N demonstrated two distinct pathways for the wurtzite and phase separation structures, and the spontaneous polarization thus calculated exhibits entirely different values. Accordingly, we demonstrated that Al 0.25 Sc 0.75 N with a phase separation structure exhibits a low polarization switching barrier of 0.15 eV/f.u. and a large spontaneous polarization of −0.77 C/m 2 ; thus, it can serve as a novel Al 1− x Sc x N-based ferroelectric material. As the dipoles in Al 1− x Sc x N with a phase separation structure are localized in the AlN region, they are individually switchable at no domain wall energy cost and are stable against extrinsic effects.