|
Journal of Physical Studies 25(2), Article 2703 [6 pages] (2021)
DOI: https://doi.org/10.30970/jps.25.2703 THERMAL AND REFRACTIVE PROPERTIES OF DOPED K2SO4 CRYSTALS IN THE REGION OF THE PHASE TRANSITION
R. Matviiv, V. Stadnyk
Ivan Franko National University of Lviv, Faculty of Physics,
|
 |
The thermal (linear expansion $Δ l/l_i(T)$, differential thermal analysis) and birefringent $Δ n_i(T)$ properties of potassium sulfate crystal with the impurity of copper with concentration 1.7 0x0p+0nd pure (for comparison) in a wide temperature range that surrounds the phase transition point have been investigated. It has been found that the introduction of an impurity causes a slight decrease in the value of $Δ l/l_i$, a shift of the point of a phase transition to the region of lower temperatures by 1.4 K approximately (the phase transition occurs at 858.6 K), and an increase in the magnitude of the jump during the phase transition, which is confirmed by DTA. Also, it has been found that the introduction of an impurity affects the temperature range where the intermediate phase exists during the phase transition. It has been established that the introduction of an impurity significantly changes the absolute value of $ n_i(T)$ as in the case of $Δ n_i(λ)$ and does not change the curves of $Δ n_i(T)$ qualitatively, the character of the dispersion remains the same as for a pure crystal, but there is only a slight change in the value of the dispersion ${\partial Δ n_i}/{\partial λ}$. Similarly to the thermal properties, the point of the phase transition shifts to the region of lower temperatures. It is assumed that the impurity of copper leads to an increase in the number of structural units in the unit cell, an increase in the stiffness of the crystal compared to nominally pure. These changes can be explained by the influence of internal stresses that occur during the introduction of the impurity, similar to the influence of uniaxial or hydrostatic pressures.
Key words: crystal, impurity, phase transition, birefringence, thermal expansion, differential thermal analysis.
