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Papers by Pavlo Shchepanskyi
2019 XIth International Scientific and Practical Conference on Electronics and Information Technologies (ELIT)
We have obtained a crystal of LiNH4SO4 in mathbfbeta\mathbf{\beta}mathbfbeta modification of good optical quality. ... more We have obtained a crystal of LiNH4SO4 in mathbfbeta\mathbf{\beta}mathbfbeta modification of good optical quality. Birefringence properties of the crystal under the action of uniaxial pressures in the wavelengths range 300–800 nm at room temperature are investigated. The character of the influence of uniaxial pressures applied along mutually perpendicular directions is defined. Studies of the temperature dependences of birefringence for 500 nm wavelength have shown that the second-order phase transition takes place at temperature 461 K, and that birefringence curves for XXX and ZZZ directions cross at 489 K. The temperature dependence of the angle between the optical axes was obtained experimentally and compared with the calculated from the refractive indices.
Visnyk of the Lviv University. Series Physics, 2017
2021 IEEE 12th International Conference on Electronics and Information Technologies (ELIT)
The temperature changes of birefringence and refractive indices of the impurity crystal of potass... more The temperature changes of birefringence and refractive indices of the impurity crystal of potassium sulfate were studied. It is found that the curves Deltaboldsymbolni(boldsymbolT)\Delta \boldsymbol{n}_{i}(\boldsymbol{T})Deltaboldsymbolni(boldsymbolT) and ni (boldsymbolT)(\boldsymbol{T})(boldsymbolT) do not change qualitatively in the case of doping, and the experimental dependences of boldsymbolni(boldsymbolT)\boldsymbol{n}_{i}(\boldsymbol{T})boldsymbolni(boldsymbolT) in the region of phase transition (PT) can be well described within the framework of the phenomenological approach of the first-order fluctuation correction to Landau theory. The introduction of the Cu2+ impurity (1.7 %) is found to cause a shift in the position of the PT point towards lower temperatures by ~ 1.4 K and a slight change in the magnitude of the boldsymbolni(boldsymbolT)\boldsymbol{n}_{i}(\boldsymbol{T})boldsymbolni(boldsymbolT) and Deltaboldsymbolni(boldsymbolT)\Delta \boldsymbol{n}_{i}(\boldsymbol{T})Deltaboldsymbolni(boldsymbolT) curves jump during PT. It is assumed, that due to an increase in structural units in the unit cell, the presence of copper impurity leads to appearance of internal stresses similar to the influence of uniaxial or hydrostatic pressures.
2021 IEEE 12th International Conference on Electronics and Information Technologies (ELIT), 2021
Ab initio calculations of the ferroelectric phase ammonium fluoroberyllate crystal (NH<inf>... more Ab initio calculations of the ferroelectric phase ammonium fluoroberyllate crystal (NH<inf>4</inf>)<inf>2</inf>BeF<inf>4</inf>(AFB) (space group <tex>$\boldsymbol{Pcn2}_{1})$</tex> in the framework of density functional theory (DFT) were conducted for the first time. Information about position of electronic levels and energy bands was obtained. It was revealed, that ferroelectric AFB has direct energy gap with a bandgap value <tex>$\boldsymbol{E}_{g}=6.79\mathbf{eV}$</tex>. Frequency-dependent dielectric functions <tex>$\varepsilon(\omega)$</tex> were calculated and analyzed.
2019 XIth International Scientific and Practical Conference on Electronics and Information Technologies (ELIT)
We have obtained a crystal of LiNH4SO4 in mathbfbeta\mathbf{\beta}mathbfbeta modification of good optical quality. ... more We have obtained a crystal of LiNH4SO4 in mathbfbeta\mathbf{\beta}mathbfbeta modification of good optical quality. Birefringence properties of the crystal under the action of uniaxial pressures in the wavelengths range 300–800 nm at room temperature are investigated. The character of the influence of uniaxial pressures applied along mutually perpendicular directions is defined. Studies of the temperature dependences of birefringence for 500 nm wavelength have shown that the second-order phase transition takes place at temperature 461 K, and that birefringence curves for XXX and ZZZ directions cross at 489 K. The temperature dependence of the angle between the optical axes was obtained experimentally and compared with the calculated from the refractive indices.
Visnyk of the Lviv University. Series Physics, 2017
2021 IEEE 12th International Conference on Electronics and Information Technologies (ELIT)
The temperature changes of birefringence and refractive indices of the impurity crystal of potass... more The temperature changes of birefringence and refractive indices of the impurity crystal of potassium sulfate were studied. It is found that the curves Deltaboldsymbolni(boldsymbolT)\Delta \boldsymbol{n}_{i}(\boldsymbol{T})Deltaboldsymbolni(boldsymbolT) and ni (boldsymbolT)(\boldsymbol{T})(boldsymbolT) do not change qualitatively in the case of doping, and the experimental dependences of boldsymbolni(boldsymbolT)\boldsymbol{n}_{i}(\boldsymbol{T})boldsymbolni(boldsymbolT) in the region of phase transition (PT) can be well described within the framework of the phenomenological approach of the first-order fluctuation correction to Landau theory. The introduction of the Cu2+ impurity (1.7 %) is found to cause a shift in the position of the PT point towards lower temperatures by ~ 1.4 K and a slight change in the magnitude of the boldsymbolni(boldsymbolT)\boldsymbol{n}_{i}(\boldsymbol{T})boldsymbolni(boldsymbolT) and Deltaboldsymbolni(boldsymbolT)\Delta \boldsymbol{n}_{i}(\boldsymbol{T})Deltaboldsymbolni(boldsymbolT) curves jump during PT. It is assumed, that due to an increase in structural units in the unit cell, the presence of copper impurity leads to appearance of internal stresses similar to the influence of uniaxial or hydrostatic pressures.
2021 IEEE 12th International Conference on Electronics and Information Technologies (ELIT), 2021
Ab initio calculations of the ferroelectric phase ammonium fluoroberyllate crystal (NH<inf>... more Ab initio calculations of the ferroelectric phase ammonium fluoroberyllate crystal (NH<inf>4</inf>)<inf>2</inf>BeF<inf>4</inf>(AFB) (space group <tex>$\boldsymbol{Pcn2}_{1})$</tex> in the framework of density functional theory (DFT) were conducted for the first time. Information about position of electronic levels and energy bands was obtained. It was revealed, that ferroelectric AFB has direct energy gap with a bandgap value <tex>$\boldsymbol{E}_{g}=6.79\mathbf{eV}$</tex>. Frequency-dependent dielectric functions <tex>$\varepsilon(\omega)$</tex> were calculated and analyzed.