Brillouin scattering study of phase transitions in LiK0.80(NH4)0.20SO4 mixed crystals Original Research Article

Brillouin spectroscopy was used to study the phase transitions of LiK0.80(NH4)0.20SO4 mixed crystals in the temperature range 10–300 K. The relevant elastic stiffness coefficients were evaluated at room temperature. The quasi-longitudinal γ16 and the quasi-transverse γ17 mode frequencies were measured in the above temperature range. From their frequency vs. temperature curve, three different phase transitions were determined. Two of the four phases presented by the crystal were found to be ferroelastic. The observed phases are tentatively assigned through a comparison with the phase transitions undergone by LiKSO4 and LiK0.96(NH4)0.04SO4 crystals. An anomalous behavior of the Brillouin linewidth near the 260 K phase transition was observed.