Temperature Dependence of the Refractive Indices of Doped K2SO4 Crystals

• Published in: Journal of applied spectroscopy 2021-09, Vol.88 (4), p.831-837
• Main Authors: Stadnyk, V. Yo, Shchepanskyi, P. A., Rudysh, M. Ya, Kogut, Z. A.
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Atomic/Molecular Structure and Spectra; Copper; Doped crystals; Impurities; Low temperature; Order parameters; Phase transitions; Physics; Physics and Astronomy; Potassium sulfate; Refractivity; Residual stress; Temperature; Temperature dependence; Transition points
• ISSN: 0021-9037; 1573-8647
• DOI: 10.1007/s10812-021-01247-8

The temperature dependence of the refractive indices of K 2 SO 4 with copper impurity was investigated. It was found that introduction of the copper impurity leads to the appearance of isotropic points [intersection of the n 2 (T) and n x (T) curves at temperature T' ~ 612 K (Δn y = 0) and n z (T) and n y (T) at temperature T″ ~ 689 K (Δn x = 0)] and also to widening of the temperature range for existence of the intermediate phase and its shift toward lower temperatures. The critical index of the phase transition order parameter was determined for the doped crystal in terms of the phenomenological approach of the first fluctuation correction to the Landau theory (β ≈ 0.17 ± 0.05). It was found that the phase transition point is shifted toward low temperatures, and this can be explained at the phenomenological level by the effect of internal stresses that arise during introduction of the impurity by analogy with the effect of uniaxial or hydrostatic pressures.