Mechanism of Reversible Field-Driven Switching in Ultra-High-Polarization Al_1-xSc_xN

Scandium-doped aluminum nitride, Al_1-xSc_xN, represents a new class of ferroelectric materials with extraordinarily high polarization, moderate coercive fields, sharp hysteresis, high temperature resilience and facile synthesizability, even in its polycrystalline form. However, the role of Sc doping in transforming unswitchable piezoelectric AlN with strong covalent bonds into a switchable ferroelectric material is not known. Here, we use ab initio quantum molecular dynamics (QMD) simulations to quantify inhomogeneity of Sc distribution, phase segregation as a function of Sc doping and understand the fundamental physics of electronic structure and covalent bonding and the nature of the potential energy surface in these alloys that simultaneously possess deep potential wells required for large polarizations (>75 μC/cm²), while retaining moderate coercive fields (< 4 MV/m). We also perform direct-switching QMD simulations in the presence of an electric field to understand the mechanism of ferroelectric switching and the critical role of local Sc concentration.