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O. Hudak

Publications and source records attributed to O. Hudak.

6 recordsLinked to original sources
arXiv2021

Mechanical and dielectric response of microcomposites of the type: ferroelastic-dielectric

Dynamic dielectric and mechanical responses of the microcomposites of the ferroelastic-dielectric type were studied in this paper. The mechanical inclusions-matrix interactions have influence on the mechanical moduli of the composite. We have studied a mechanical response of the composite which consists of the material M and of the other material I in which dispersion of mechanic moduli of particles is present. The inclusions of the dielectric material in the ferroelastic matrix has the effect on the dielectric response of the microcomposite. We have found conditions for which the inclusions have the effect of enhancement of the dielectric response. Results of low frequency dielectric constant and dielectric loss in orthorhombic $ Al_{2}(WO_{4})_{3}$ show for polycrystalline material, where voids play the role of the dielectric material, their linear increasing dependence on increasing hydrostatic pressure p. These facts are qualitatively explained within our theory.

cond-mat.mtrl-sci↗
arXiv2016

On Static Dielectric Response of Microcomposites of the Type Ferrolastics-Dielectrics For Application in Solid Oxide Fuel Cells (SOFC)

We describe the static dielectric response of ferroelastic-dielectric microcomposites. Dependence on temperature, pressure and concentration is considered for temperatures in the paraelastic transition. In recent years there has been considerable interest in perovskite oxides for application in solid oxide fuel cells (SOFC), exhaust gas sensors in automobiles, membranes for separation processes and as catalysts, which are of the ferroeleastic nature, f.e. of the ($ LaSrCoO_{3}$) type. Ferroelastic-dielectric microcomposites and measurement of their properties may improve properties of perovskite oxides for these applications.

cond-mat.mtrl-sci↗
arXiv2008

Paraelectric - Ferroelectric Phase Transitions in Particles of the Sphere Shape

A transition in a spheroidal particle from the paraelectric to the ferroelectric phase as well as dynamic susceptibility are studied without approximation in the paraphase. It is assumed that the surface charge is compensated and the boundary condition for the polarisation is P=0, i. e. with zero polarisation at the surface of the particle. There is an infinite number of resonance frequencies in the dynamic dielectric function within the quasistatic approximation. The paraphase properties of the dielectric response of the particle are discussed. The transition temperature decreases with decreasing diameter d of the particles inverse quadratically. There exists such a critical diameter that for the particles with the diameter below the critical one the ferroelectric phase is absent. Comparison of the experiment with theoretical results is carried out. Introduction of a dead layer thickness leads to a very good agreement of theory with the experiment for $PbTiO_{3}$ and to a good agreement with the experimentfor $BaTiO_{3}$.

cond-mat.mtrl-sci↗
arXiv2007

Quantum Critical Phenomena, Entanglement Entropy and Hubbard Model in 1d with the Boundary Site with a Negative Chemical Potential -p and the Hubbard Coupling U Positive

Recently the ground state and some excited states of the half-filled case of the 1d Hubbard model were discussed for an open chain with L sites. Authors considered the case when the boundary site has a negative chemical potential -p and the Hubbard coupling U is positive. They have shown by an analytic method that when p is larger than the transfer integral some of the ground-state solutions of the Bethe ansatz equations become complex-valued. They have found that there is a surface phase transition at some critical value p_c; when p < p_c all the charge excitations have the gap for this case, while there exists a massless charge mode when p > p_c. To find whether this surface phase transition is of the first order or of the second order we have used the entanglement entropy concept. The entropy and its derivative has a discontinuity there, so this transition is of the first order.

cond-mat.str-el↗
arXiv2006

Mechanical and Dielectric Response of PZT and Tetragonal to Monoclinic Phase Transition: I. Theory

The PZT material near the morphotropic phase boundary where a monoclinic phase was observed is studied. A theory of the tetragonal to monoclinic phase transition was developed within the Landau free energy approach. The phase transition from the tetragonal to the monoclinic phase is of the first order near the second order. Dielectric response near the phase transition from the tetragonal to the monoclinic phase was studied for the crystal and for the ceramic and polycrystalline material taking into account the diagonal 33 and the off diagonal 31 components of susceptibility. The later diverges at temperature of stability boundary for the monoclinic phase, and it is zero in the tetragonal phase. Such a behavior is not observed in the effective dielectric static constant for ceramics and polycrystalline materials. We explain absence of a large contribution of the off diagonal susceptibility by a grain structure of the material. Above the percolation transition the off diagonal contribution to the effective susceptibility is not present. Effective susceptibility which is decreasing in tetragonal phase is in the monoclinic phase also decreasing, however below phase transition temperature the decrease is slower. A quantitative theoretical behavior of dielectric susceptibility for both phases is found. Mechanical response of PZT material to a uniaxial stress is studied theoreticaly for both phases. Observed temperature behavior of it, a well around the transition temperature from the tetragonal to monoclinic phase transition, is qualitatively explained.

cond-mat.mtrl-sci↗