Orthorhombic-like atomic arrangement in hafnium-oxide-based nanoparticles

Size effect on ferroelectricity in nanoparticles (NPs) has been an important issue for decades. For NPs with a perovskite-type crystal structure, which are the most popular ferroelectrics, ferroelectricity is believed to disappear for sizes below a critical value. However, newly discovered hafnium-oxide-based systems exhibit stronger ferroelectricity for thinner films that may be advantageous to produce smaller ferroelectric NPs, and the ferroelectricity is believed to originate from a polar orthorhombic phase. In the present study, zirconium-doped hafnium oxide NPs with diameters of ∼3−4 nm were synthesized and then were clarified to be of a metastable phase with an orthorhombic-like local atomic arrangement. This study implies that ferroelectricity may possibly be obtained in hafnium-oxide-based NPs.