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1
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Temperature-and-Spectral Deformations of the Optical Indicatrix of Rubidium Sulphate Single Crystal

100%
Gaba V.
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issue 1
129-132
EN
The paper deals with newly investigated temperature-and-spectrum dependences of principal birefringences (Δ n_{i}(λ,T)-i=X, Y, Z; λ=250÷850 nm; T = 4.2-1100 K), and temperature dependence of the optic-axial angle (2V(T) - T=4.2-1100 K) for two laser lines 632.8 nm and 441.1 nm of Rb_{2}SO_{4} crystals. Based on the temperature dependence of the optic-axial angle, the second point of birefringence sign inversion has been found. Newly obtained is the temperature-and-spectrum diagram of the uniaxial state of the optical indicatrix at the "isotropic points" and in the hexagonal phase of Rb_{2}SO_{4}. Based on the temperature behavior of the birefringence and optic-axial angle it was supposed that hexagonal-orthorhombic phase transition in rubidium sulfate can be a second-order phase transition. Found is the inversion of birefringence dispersion in the X and Y directions at 400 K and 620 K, respectively.
2
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Baric Shift of Phase Transition in Ammonium Sulfate Crystals

100%
Gaba V.
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issue 1
126-128
EN
The influence of uniaxial mechanical pressures (σ_m ≤ 200 bar) on the spectral (300-800 nm) and temperature (77-300 K) dependences of the refractive indices n_{i}, the birefringence Δn_{i} and the phase transition point in ammonium sulfate crystals are studied. It is established that the uniaxial pressure does not change character of the dispersion dn_{i}/dλ, but only its value λ The shift of the phase transition in ammonium sulfate under the uniaxial mechanical pressure is analyzed.
3
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Birefringence of Mechanically Stressed Potassium Tetrachlorine Zincanate Crystals

51%
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.
4
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Influence of Uniaxial Pressure on the Refractive Properties of Rubidium Tetrachlorine Zincanate Crystals

51%
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.
5
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The Influence of Partial Isomorphic Substitution on Electronic and Optical Parameters of ABSO₄ Group Crystals

39%
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.
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