Grain-size effects prevent formation of stable monoclinic phases in Hf_0.5Zr_0.5O₂ nanoparticles

Abstract

Ferroelectricity in hafnium dioxide (HfO₂)-based thin films originates from a metastable orthorhombic phase. Therefore, the formation of other phases, such as monoclinic (m) phase, should be avoided. Here, grain-size effects on transformations to the m phase in zirconium-doped HfO₂ nanoparticles were examined. X-ray diffraction and electron microscopy revealed that only a fraction transformed into the m phase via 900-°C annealing and the m-phase particles exceeded 50 nm. Thus, grain size alone was a critical factor to avoid forming the m phase.