Ferroelectric phase stabilization of HfO₂ by nitrogen doping

We report that nitrogen (N) doping can drive the ferroelectricity of HfO 2 . It was found that N doping can cause the transition from a monoclinic phase to a highly symmetric phase. The role of N doping is discussed from the viewpoints of charge balance and bond-constraining effects. The former is responsible for the structural transformation from a paraelectric phase to a ferroelectric phase by forming an oxygen vacancy. In addition, Hf–N and N–O bonds with covalent characteristics have strong effects on HfO 2 structural and electrical properties, and thus contribute to a marked HfO 2 para-/ferroelectric transition.