arXiv subjects

Juliya M. Gudenko

Publications and source records attributed to Juliya M. Gudenko.

4 recordsLinked to original sources

arXiv2026

Influence of BaTiO_3 nanoparticles on the anisotropy of the dielectric properties of nematic liquid crystal 5CB

This work is devoted to the mechanisms of dielectric response and electric conductivity of suspensions consisting of the nematic liquid crystal 5CB with different concentrations (from 0 to 10 wt.%) of ferroelectric BaTiO_3 nanoparticles with an average size of 24 nm. We revealed that the incorporation of nanoparticles influences significantly the dielectric permittivity magnitude and anisotropy, as well as dielectric losses of the suspension. A pronounced temperature dependence of the anisotropic dielectric permittivity of the suspensions was found at lower temperatures corresponding to the mesophase state; but it is also present at higher temperatures corresponding to the isophase. The dependence of the mesophase-isophase transition temperature on the concentration of BaTiO_3 nanoparticles appeared nonmonotonic. With increasing temperature, both the capacitance and the electrical resistance of the pure liquid crystal increase, as well as it increases in the suspensions with small concentration of BaTiO_3 nanoparticles. Due to space charge accumulation in the shells of nanoparticles, larger concentrations of BaTiO_3 nanoparticles influence strongly the ionic transport by promoting the formation of ionic-electronic screening. This effect modifies the dielectric properties and conduction mechanisms of the suspension, leading to the nonmonotonic dependence of the mesophase - isophase transition temperature versus the nanoparticle concentration.

cond-mat.mtrl-sci↗

arXiv2025

Dynamics of charge states at the surface of a ferroelectric nanoparticle in a liquid crystal

The liquid crystal with suspended ferroelectric nanoparticles is an interesting object for fundamental research of the long-range dipole-dipole interactions; as well as it is promising for optical, optoelectronic and electrochemical applications. Such suspensions can serve as basic elements for advanced nonvolatile memory cells and energy storage devices. The work studies the cells filled with a nematic liquid crystal 5CB and the cells containing 5CB with 0.5 wt.% and 1 wt.% of BaTiO3 nanoparticles with an average size of 24 nm. We analyzed the time dependences of the current flowing through the cells at constant applied voltage and the voltage dynamics in the no-load mode. The time dependences of the current and voltage show a slowing down decay rate. For the cells with BaTiO3 nanoparticles, the decrease in the decay time is characteristic. A possible physical reason for the retarding decay time rate is the indirect effect of screening charges, which cover ferroelectric nanoparticles, and slow ionic transport in the liquid crystal. To explain the dynamics of current and voltage, the finite element modeling of the polarization distribution, domain structure dynamics, and charge state of nanoparticles in a liquid crystal is performed using Landau-Ginzburg-Devonshire approach. Theoretical results confirmed the leading role of screening charges, because the surface of a ferroelectric nanoparticle adsorbs an ionic-electronic charge that partially screens its spontaneous polarization in single-domain and/or poly-domain states. When an electric field is applied to the liquid crystal with nanoparticles, it can release part of the screening charge (mainly due to the change in the polarization of the nanoparticle), which will lead to a decrease in decay time rate of the current and voltage dependences.

cond-mat.mtrl-sci↗

arXiv2025

Resistive switching and charge accumulation in Hf0.5Zr0.5O2 nanoparticles

We revealed the resistive switching, negative differential resistance and charge accumulation effects in Hf0.5Zr0.5O2 nanopowders sintered by the auto-combustion sol-gel method and annealed at temperatures from 500°C to 800°C. The fraction of the orthorhombic phase, determined by the X-ray diffraction (XRD), decreases from 91 vol.% to 7 vol.% with an increase in the annealing temperature from 600°C to 800°C. The electron paramagnetic resonance (EPR) spectra reveal the great amount of oxygen vacancies in the annealed samples, at that the decrease of the 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 Hf0.5Zr0.5O2 powders. To explain the results of electrophysical measurements, we compare the features of the current-voltage characteristics with the phase composition of the Hf0.5Zr0.5O2 powders and with the peculiarities of their EPR spectra. The analysis allows us to relate the resistive switching and charge accumulation observed in Hf0.5Zr0.5O2 nanopowders with the appearance of the ferroelectric-like polar regions in the orthorhombic phase of the nanoparticles, which agrees with the calculations performed in the framework of Landau-Ginzburg-Devonshire approach and density functional theory.

cond-mat.mtrl-sci↗

arXiv2024

Ferroelectric Nanoparticles in Liquid Crystals: The Role of Ionic Transport at Small Concentrations of the Nanoparticles

We reveal the visible influence of the ultra-small concentrations (1 wt.% or less) of the BaTiO3 nanoparticles (average size 24 nm) on the current-voltage characteristics and capacitance of the dielectric liquid crystal (LC) 5CB. The pure LC cell demonstrates higher current (and thus smaller resistance) than the LC cells filled with a very small concentration (0.5-1) wt.% of BTO nanoparticles. The same trend is observed for the charge-voltage characteristics: the capacitance loop is the widest for the pure LC cell and becomes noticeably thinner in the presence of (0.5-1) wt.% of BaTiO3 nanoparticles. This seems counterintuitive, because 1 wt.% of ferroelectric nanoparticles very slightly modify the effective dielectric response and should not influence on the director distribution and elastic properties of the LC. We conclude that a possible physical reason of this observation is the influence of the ionic-electronic screening charges, which cover the ferroelectric nanoparticles and become polarized in the external field, on the ionic transport in the LC.

cond-mat.mtrl-sci↗