Matviiv R. The influence of impurities on the optical and electronic parameters of sulfate group dielectric crystals

Potassium sulfate (PS) crystals doped with copper ions with concentrations of impurity of 1.7% and 3% were synthesized. The structure of impurity crystals was studied by the X-ray powder diffraction method. It is established, that it can be considered as a result of multiple (two potassium atoms per copper atom) heterovalent substitution. Dispersions of refractive indices of potassium sulfate crystals doped with copper ions with the 1.7 and 3% impurity concentration are studied for the first time by the Obreimov method in the spectral range 300… 700 nm and for thre principal crystal optics directions. It is established that the introduction of impurity leads to a decrease in the absolute values of the refractive indices and does not change the nature of the dispersion. The spectral (300… 700 nm) dependences of birefringence of potassium sulfate crystals doped with copper ions with different concentrations of impurity (1.7 and 3%) are investigated by the spectroscopic method. The influence of uniaxial pressures and temperature changes on birefringence is investigated. It is established that the introduction of impurity changes the absolute values of birefringence. It is also established that uniaxial pressure changes the magnitude of the absolute values of birefringence. It is found the presence of two birefringence-sign-inversion points in doped with copper ions PS crystals. It is shown that the introduction of impurity leads to the shift of birefringence-sign-inversion points towards low temperatures if compared with that of pure crystal. Generalized temperature-spectral-baric diagrams of the isotropic state of doped with copper ions PS crystals are constructed, which may be of practical importance when using this crystal as a crystal-optical sensor. The study of thermal expansion, differential thermal analysis, and birefringence of potassium sulfate crystals doped with copper ions is carried out in the wide temperature range, covering the phase transition point. The values of the combined and absolute piezooptical coefficients of doped PS crystals are investigated. Slight decrease of the coefficients in comparison with that of pure crystal was revealed, which indicates an increase in the mechanical stiffness of impurity crystals. Calculations of the band-energy structure of PS crystals doped with copper ions with the 3% impurity concentration were performed using density functional theory. It was found that there are levels of copper d-electrons in the band gap, which remove their degeneration due to the action of the crystal field. In order to confirm the calculated band-energy structure, the X-ray photoelectron and X-ray emission spectra of the PS crystals doped with copper were studied. The experimental results have confirmed the results of theoretical calculations of the band-energy structure. It is proposed to use the K1.75[NH4]0.25SO4 crystal as a thermosensitive element in a device for measuring temperature. It is also proposed to use the ammonium beryllium fluoride crystal as a piezoelectric element in the pressure measuring device.