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1
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Optical Investigations of Phase Transitions in (NH_{4})_{2}SbF_{5} Crystal

100%
Andriyevsky B., Czapla Z., Stadnyk V.
Acta Physica Polonica A
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1995
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vol. 87
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issue 3
611-617
EN
Results of optical thickness and refractive indices measurements for (NH_{4})_{2}SbF_{5} crystal in the temperature range 100-310 K are presented. The measurements were done with interference method using He-Ne laser (λ = 632.8 nm). At T_{c1} = 292 K and T_{C2} = 168 K two continuous phase transitions with critical indices β_{1} = 0.38 and β_{2} ≤ 0.57 were observed. Ad­ditional anomaly of temperature changes of interference order with maximum at T_{c3} ≈ 132 K were found. This anomaly resembles a diffused transition. Temperature-averaged values of derivatives of refractive indices dn_{g} /dT = -3.3 × 10^{-5} K and dn_{m}/dT = -2.9 × 10^{-5} K^{-1} evidenced a decrease in optical anisotropy (birefringence) along the b-axis on heating run.
2
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Birefringence of Mechanically Stressed Potassium Tetrachlorine Zincanate Crystals

100%
Stadnyk V., Gaba V., Kohut Z.
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issue 1
133-135
EN
The spectral and baric dependences of the birefringence Δn_{i} of K_{2}ZnCl_{4} crystals were studied. It is shown that the dispersion Δn_{i}(λ) is normal and sharply increases on approaching the absorption edge. It is established that the uniaxial pressures do not change the character but only the values of the dispersions dΔn_{i}/dλ and temperature dependences of dΔn_{i}/dT.
3
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Influence of Uniaxial Pressure on the Refractive Properties of Rubidium Tetrachlorine Zincanate Crystals

100%
Stadnyk V., Gaba V., Kohut Z., Popel O.
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issue 1
136-138
EN
The effect of uniaxial pressure (σ_m ≤ 200 bar) on the spectral (300-800 nm) and temperature (77-300 K) dependences of the refractive indices of Rb_{2}ZnCl_{4} crystals are investigated. The baric dependences of the electron polarizability, specific refraction and the parameters involved in the Sellmeier formula are calculated.
4
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Behaviour of Isotropic Point in LiKSO_{4} Crystals

100%
Stadnyk V., Romanyuk M., Vachulovich V.
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EN
The temperature-spectral dependencies of refractive indices and birefringence in wide temperature (77-1000 K) and spectral (250-850 nm) regions in LiKSO_{4} crystals were measured. The isotropic point of LiKSO_{4} crystals was investigated. It was shown that annealing and X-ray irradiation display insignificantly the isotropic point to a visible region of spectrum.
5
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The Influence of Partial Isomorphic Substitution on Electronic and Optical Parameters of ABSO₄ Group Crystals

76%
Shchepanskyi P., Gaba V., Stadnyk V., Rudysh M., Brezvin R., Piasecki M.
Acta Physica Polonica A
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2018
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vol. 133
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issue 4
819-823
EN
First principles calculations of band energy, density of states and dielectric function of K_{1.75}(NH₄)_{0.25}SO₄ single crystals in Pnma structure is performed in the framework of density functional theory. In order to describe the exchange-correlation interaction the general gradient approximation and local density approximation are used. Character and genesis of main energy bands of the crystal are discussed and comparison with data set for K₂SO₄ isomorphic crystal performed. The influence of partial isomorphic substitution K→ NH₄ found itself mainly in altering the bottom of conduction band and decrease of band gap value. From the dielectric functions dependences, the refractive indices dispersion and absorption coefficient spectra are deduced. Obtained refractive indices satisfactorily agree with experimental data in the visible spectrum region.
6
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Specific Features of Content Dependences for Energy Gap in In_{x}Tl_{1-x}I Solid State Crystalline Alloys

64%
Kashuba A., Piasecki M., Bovgyra O., Stadnyk V., Demchenko P., Fedorchuk A., Franiv A., Andriyevsky B.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
68-75
EN
A series of In_{x}Tl_{1-x}I (x=0.4-0.9) single crystalline solid state alloys were successfully synthesized by the vertical Bridgman method. For the first time the density functional theory based band structure calculations are performed and features of the band energy dispersion are discussed. Comparison with the experimental energy gap E_{g} obtained from the optical photoconductivity is discussed. An essential role of the localized defects and excitons in formation of the edge photoconductivity is analyzed. Relation between the crystal structure and photoconductivity of the materials studied is discussed. Also the origin of the principal valence and conduction bands is explored. Experimental measurements of the band gap E_{g} by the optical and photoconductivity methods have given opposite dependences with respect to the indium content x. Features of the photoconductivity spectra for different crystallographic directions have been discussed with taking into account the chemical bonds anisotropy.
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