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arXiv2026

Correlations of Spectroscopic and Dielectric Properties of Hafnia-Zirconia Nanoparticles

In this work we analyze correlations of X-ray photoelectron and diffraction spectra, and dielectric properties of hafnia-zirconia nanoparticles (the chemical compositions Hf0.4Zr0.6O2 and Hf0.6Zr0.4O2, and the average size of 7.5 nm) prepared by the solid-state organo-nitrate synthesis and annealed in air. The phase state of the nanoparticles, determined by the X-ray diffraction spectroscopy, is the coexistence of the nonpolar monoclinic (42 - 76 mass %) and orthorhombic (56 - 24 mass %) phases. Concentration of the oxygen vacancies was estimated from the X-ray photoelectron spectroscopy. The increase in the intensity of the dielectric permittivity maximum observed near 350 - 450 K in a PVDF matrix with embedded Hf0.4Zr0.6O2 nanoparticles can be related with an increase in oxygen vacancy concentration. Theoretical calculations, based on Landau-Ginzburg-Devonshire theory, explain the increase of the dielectric permittivity in Hf0.4Zr0.6O2 nanoparticles compared to Hf0.6Zr0.4O2 nanoparticles.

cond-mat.mtrl-sci↗

arXiv2026

Role of Oxygen Vacancies in Stabilizing the Orthorhombic Phases of Hf0.5Zr0.5O2 Nanoparticles

In this work we study the stabilization of the orthorhombic phases in small Hf0.5Zr0.5O2 nanoparticles (average size ~ 7 nm) annealed under different oxygen partial pressures. Concentration of the oxygen vacancies, which is determined by annealing conditions, was estimated from the electron paramagnetic resonance spectra and X-ray photoelectron spectroscopy. The fraction of the orthorhombic phases, that is determined by the X-ray diffraction and nuclear magnetic resonance, depends on the concentration of oxygen vacancies. Phenomenological calculations based on Landau-Ginzburg-Devonshire theory considering trilinear coupling between nonpolar, antipolar and polar phonon modes, indicate that chemical strain induced by oxygen vacancies can stabilize the orthorhombic phase o-III with the ferroelectric long-range ordering in small Hf0.5Zr0.5O2 nanoparticles. The theory confirms the stability of ferroelectric polarization in the vacancy-enriched Hf0.5Zr0.5O2 nanoparticles. The increase in the intensity of the dielectric permittivity maximum, observed near 350 - 380 K in the PVDF matrix with the Hf0.5Zr0.5O2 nanoparticles annealed in the CO+CO2 atmosphere, is clearly associated with the increase in oxygen vacancies concentration. The vacancies lead to the defect-induced elastic dipole formation and to the increase in ionic conductivity, which decreases the depolarization field and may induce the ferroelectric-like phase transition in the vacancy-enriched Hf0.5Zr0.5O2 nanoparticles. Due to the interfacial effects the negative capacitance states may be realized in weakly screened and spatially isolated Hf0.5Zr0.5O2 nanoparticles embedded in the PVDF matrix.The present approach based on oxygen-vacancy-induced elastic and screening effects may provide a route for engineering ferroelectric-like states in other nanoscale ferroic oxides.

cond-mat.mtrl-sci↗