The Effect of Uniaxial Pressures on the Infrared Spectra of LiNH4SO4 Crystals

Abstract

The infrared reflection spectra of mechanically free and uniaxially compressed LiNH₄SO₄ crystals are studied for the first time in the spectral range of 800–1700 сm^–1 along three crystallophysical directions. The Kramers–Kronig dispersion relations are used to determine the dispersion and baric dependences of refractive index n and the real ε₁ and imaginary ε₂ parts of the dielectric constant and to calculate the frequencies of longitudinal ω_LO and transverse ω_ТO vibrations, decay constant γ, and oscillator strength f of mechanically free and compressed LiNH₄SO₄ crystals. The considerable changes observed in the main reflection bands are explained by the effect of uniaxial pressures on the NH₄ and SO₄ tetrahedra.