Abstract
The infrared reflectance spectra of a mechanically free or uniaxial-pressure-confined (NH4)2SO4 crystal were studied for the first time in the spectral range 800–1700 cm−1 in three crystallographic directions. Using the Kramers-Kronig relations, the dispersion and pressure dependences of the following quantities are obtained: the index of refraction n, the real (ɛ1) and imaginary (ɛ2) parts of the permittivity, the frequencies of longitudinal (ωLO) and transverse (ωTO) optical vibrations, the damping constant γ, and the oscillator strength f of the mechanically free or clamped (NH4)2SO4 crystal. A considerable change in the main reflection bands with pressure was observed, which is due to the effect of uniaxial pressure on the NH4 and SO4 tetrahedral frames.
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