| Autor: |
Romanyuk, M. O., Stadnyk, V. Yo., Kurlyak, V. Yu., Andriyevskiy, B., Kushnir, O. S., Brezvin, R. S. |
| Zdroj: |
Journal of Physical Studies; 2014, Vol. 18 Issue 4, p1-23, 23p |
| Abstrakt: |
We describe the effect of uniaxial pressures on the refractive indices ni, the birefringences Δni, and the characteristics of optical oscillators for K2SO4 crystals. The uniaxial compression is shown not to change the nature of the dispersion effect but to influence only its magnitudes dni/dλ and dΔni/dλ. It is established that the increase in ni due to the uniaxial pressure is mainly caused by changing parameters of the oscillators and their effective density. We find that a simultaneous application of the pressures can lead to the apprearance of new isotropic states in K2SO4 crystals. We have also found significant baric shifts of the ferroelastic phase transition (PT) point and the temperature interval where an intermediate phase exists near that PT. We have calculated spectral and temperature changes in the absolute piezooptic constants of K2SO4 crystals and have found intersections of π13 (T) and π31 (T) curves and π21 (T) and π32 (T) curves at the temperatures that correspond to positions of their isotropic points. The electronic band structure of K2SO4 is calculated, and the nature of their valence and conduction bands is ascertained. The uniaxial pressures σ < 1.5 GPa applied along the principal crysatallographic directions impose an increasing bandgap Eg . The experimental results obtained for the refractive indices near the PT are shown to be satisfactorily described in the framework of phenomenological approach of a first fluctuation correction to the Landau theory when taking into account the influence of point structural defects on the ni (T) behavior in the vicinity of small relative temperatures. A generalized temperature-spectral-baric diagram of the isotropic state is constructed for the K2SO4 crystals. A method for monitoring the Δni magnitude in optically biaxial crystals is suggested, which is based on the measurements of the conoscopic pattern parameters. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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