Phase diagrams and polarization reversal in nanosized HfxZr1−xO2−y

Abstract

To describe the polar properties of nanosized HfxZr1−xO2−y, we evolve the “effective” Landau–Ginzburg–Devonshire (LGD) model based on the parametrization of the Landau expansion coefficients for polar and antipolar orderings. We have shown that the effective LGD model can predict the influence of screening conditions and size effects on phase diagrams, polarization reversal, and structural properties of nanosized HfxZr1−xO2−y of various shapes and sizes. To verify the model, we use the available experimental results for HfxZr1−xO2 thin films and oxygen-deficient HfO2−y nanoparticles prepared under different annealing conditions. X-ray diffraction, which was used to determine the phase composition of the HfO2−y nanoparticles, revealed the formation of a ferroelectric orthorhombic phase in them. Micro-Raman spectroscopy was used to explore the correlation of lattice dynamics and structural changes that depend on the oxygen vacancy concentration in the HfO2−y nanoparticles. Since our approach allows us to determine the conditions (shape, sizes, Zr content, and/or oxygen vacancy amount) for which nanosized HfxZr1−xO2−y are ferroelectric or antiferroelectric, we hope that the obtained results are useful for creation of next generation Si-compatible ferroelectric gate oxide nanomaterials.