Volume-matched piezoelectric LaN/REN superlattices from first-principles

Abstract

LaN/rare earth nitride (REN) superlattices, having magnetic REN as one of the parent components, are constructed and studied by first-principles calculations. In particular, they are found to be mechanically and dynamically stable with (anti-)ferromagnetic and ferroelectric orderings. We reveal that the volume matching condition is applicable to these superlattices, which results in the elastic constant C33 softening and, when combined with a small c/a value, induces a huge piezoelectric response near the unstrained state. We also show that in-plane biaxial strain can precisely control the nature (indirect or direct) and value of the electronic bandgap. Moreover, the unpaired magnetically active 4f-electrons reduce the c-direction off-centric distortion of the wurtzite structure, making possible the switching of the ferroelectric polarization. This work, therefore, reveals that the volume matching condition also applies to magnetic materials and provides guidance for the design of multiferroic rare-earth nitride superlattices in piezoelectric devices.