Stabilizing Polar Phases in Binary Metal Oxides by Doping

       Ferroelectric materials have a spontaneous electric polarization that can be switched between two or more orientations with an applied electric field. They enable devices such as nonvolatile random-access memories, ferroelectric field-effect transistors, and ferroelectric tunnel junctions. The discovery of ferroelectricity in simple binary metal oxides, such as Ga₂O₃, HfO₂ and ZrO₂, is attractive as they can be easily integrated with Si devices. However, the ferroelectric phase in these binary metal oxides is usually metastable and can only be stabilized on proper substrates under specific growth conditions. Here, we show that doping in these binary metal oxides can efficiently modulate the relative stability of their polar and non-polar phases. By using a polarized charge-spring model and DFT calculations, we show that doping facilitates charge redistribution on anion lattice because of the difference of their on-site Coulomb energy. We further show that experimentally the doping enhanced stabilization of the polar phase can be achieved using cation- or anion-substitution, interlayer charge transfer or even by the formation of point defects.