Prof. Alexander A. Molnar

The low-frequency dielectric susceptibility of layered CuInP₂(Se_xS_1−x)₆ mixed crystals is investigated. The morphotropic phase boundary is found between x = 0.75 and 0.8. Broadening of phase transition anomalies in CuInP₂S₆ is observed at substitution of sulfur atoms by selenium. At substitution of selenium by sulfur in CuInP₂Se₆ a second order phase transition from the paraelectric phase to an intermediate phase is clearly observed up to the morphotropic boundary, while dielectric anomalies at the first order transition from the intermediate phase to ferrielectric phase are completely extinguished.

1 December 2016 in Low Temperature Physics

Journal Article

Valence fluctuations in Sn(Pb)2P2S6 ferroelectrics

R. Yevych

V. Haborets

M. Medulych

Alexander A. Molnar

A. Kohutych

Yu. Vysochanskii

The valence fluctuations which are related to the charge disproportionation of phosphorous ions P4++P4+→P3++P+5 are the origin of ferroelectric and quantum paraelectric states in Sn(Pb)2P2S6 semiconductors. They involve recharging of SnPS3 or PbPS3 structural groups which can be represented as half-filled sites in the crystal lattice. Temperature–pressure phase diagram for Sn2P2S6 compound and temperature-composition phase diagram for (PbySn1–y)2P2S6 mixed crystals, which include tricritical points and where a temperature of phase transitions decrease to 0 K, together with the data about some softening of low energy optic phonons and rise of dielectric susceptibility at cooling in quantum paraelectric state of Pb2P2S6 are analyzed by GGA electron and phonon calculations and compared with electronic correlations models. The anharmonic quantum oscillators model is developed for description of phase diagrams and temperature dependence of dielectric susceptibility.

10 September 2018 in Physical Review Applied

Journal Article

Double Hysteresis Loops in Proper Uniaxial Ferroelectrics

J. Banys

In bulk proper uniaxial ferroelectrics, double antiferroelectriclike hysteresis loops are observed in the case of

{Sn}_{2} P_{2} S_{6}

crystal. The quantum-anharmonic-oscillator model is proposed for the description of such a polarization-switching process. This phenomenon is related to the three-well local potential of the spontaneous-polarization fluctuations at a distinctive negative ratio of coupling constants that correspond to intersite interaction in the given sublattice and interaction between two sublattices of the modeled

{Sn}_{2} P_{2} S_{6}

crystal structure. The data obtained can be used for the development of multilevel-cell-type memory technology.

About Me

In 1982, I graduated from secondary school in Uzhhorod and entered the Faculty of Physics at Uzhhorod State University. After my first year, I served in the Soviet Army (1983–1985) as an instructor in digital training systems. In 1989, I graduated with honors as an engineer-physicist and began postgraduate studies in semiconductor physics. Since 1992, I have been engaged in scientific research at Uzhhorod National University. In 1994, I defended my PhD dissertation on dielectric relaxation in spontaneously polarized semiconductors and became a senior researcher at the Institute of Solid State Physics and Chemistry. From 2001 to 2004, I pursued doctoral studies. Between 2009 and 2020, I served as an associate professor of Semiconductor Physics, receiving the academic title in 2015. In 2019, I earned the degree of Doctor of Physical and Mathematical Sciences with a dissertation on relaxation phenomena in phosphorus-containing chalcogenide crystals. Since 2020, I have been a professor in the Department of Semiconductor Physics and received the academic title of Full Professor in 2023. I also serve as a leading researcher at the Institute of Solid State Physics and Chemistry.

Prof. Alexander A. Molnar

Prof. Alexander A. Molnar

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