Tuzyak M. Optic-spectral characteristics of uniaxially stressed ammonium sulfate crystals

The influence of uniaxil pressure action upon the infrared reflection spectra of crystals is studied. Using the Kramers-Kronig relation dispersion the dispersive and baric dependences of optical constants (absorption coefficient, real and imaginary part of the dielectric constant) are studied. The parameters of infrared dispersion (the frequencies of the longitudinal and the transverse vibrations, the oscillator strengths and attenuation constant) were calculated both the mechanically free and the uniaxially stressed crystals (NH4)2SO4. It is revealed that the ni values mainly increase under the action of uniaxial stresses. These facts are caused by the increment of the electron polarizability, the bonds refraction and the displacement of the absorption spectra to the long-wave region. The uniaxial pressure along the principal crystalophysical axes is shown to give rise to shifting the PT points towards higher or lower temperatures, depending on the influence of uniaxial pressures upon the crystallinestructure. The anomalies of optical properties at the phase transition are due to the rise of spontaneous polarization and deformation.