Abstract. In this work, the relationship between the crystalline structure symmetry, concentration of point defects and possible appearance of ferroelectric-like polarization in HfO_2–y nanoparticles was established. The X-ray diffraction and electron paramagnetic resonance analyses revealed the formation of ferroelectric-like orthorhombic phase in oxygen-deficient HfO_2–y nanoparticles (pure and doped with rare-earth element yttrium ones). Density functional theory (DFT) calculations showed that small HfO₂ nanoparticles may become polar, especially in the presence of impurity atoms and/or oxygen vacancies. To explain the experimental results, we modified the effective Landau–Ginzburg–Devonshire (LGD) model using the parameterization approach, focusing on the Landau expansion coefficients associated with polar and antipolar orderings, which agrees with the performed DFT calculations. The effective LGD model may be useful for developing silicon-compatible ferroelectric nanomaterials based on
Hf_xZr_1–xO_2–y.