Resistive Switching and Charge Accumulation in Hf0.5Zr0.5O2 Nanoparticles

We revealed the resistive switching, negative differential resistance, and charge accumulation effects in Hf_0.5Zr_0.5O₂ nanopowders sintered by the autocombustion sol–gel method and annealed at temperatures from 500 to 800 °C. The fraction of the tetragonal and/or orthorhombic phases, determined by the X-ray diffraction (XRD), decreases from 91 to 7 vol % with an increase in the annealing temperature from 600 to 800 °C. The electron paramagnetic resonance (EPR) spectra reveal the great amount of oxygen vacancies in the annealed samples, and that the decrease of the tetragonal/orthorhombic phase fraction (observed with an increase in the annealing temperature) correlates with a decrease in the intensity of EPR spectral lines associated with the oxygen vacancies and impurities. This indicates the participation of oxygen vacancies and other defects in the formation of the orthorhombic phase in the Hf_0.5Zr_0.5O₂ powders. To explain the results of electrophysical measurements, we compare the features of the current–voltage characteristics to the phase composition of the Hf_0.5Zr_0.5O₂ powders and with the peculiarities of their EPR spectra. The analysis allows us to relate the resistive switching and charge accumulation observed in Hf_0.5Zr_0.5O₂ nanopowders with the possible appearance of the ferroelectric-like polar regions in the nanoparticles, which agrees with the calculations performed in the framework of the Landau–Ginzburg–Devonshire approach and density functional theory.