Fundamental absorption edge and normal dispersion of β-LiNaSO4 single crystal

• I study the fundamental absorption edge and dispersion of β-LiNaSO4 crystal.
• β-LiNaSO4 crystal shows normal dispersion at photon energies lower than 4.7 eV.
• The optical data of β-LiNaSO4 crystal obey the known dispersion relations.
• I calculate normal dispersion parameters of β-LiNaSO4 crystal for the first time.
• Single oscillator energy and optical energy gap values obey the relation E0≈1.5Eg.

Lithium sodium sulfate (LiNaSO4)single crystal is synthesized and grown by the slow evaporation of supersaturated aqueous solution at constant temperature (303 K). Powder X-ray diffraction is measured at room temperature in order to identify the grown crystal. Transmittance and reflectance measurements are used to study the optical properties of this crystal at room temperature phase (β-LiNaSO4). The type of transition is determined. The values of optical energy gap, phonon energy and phonon equivalent temperature are calculated. Refractive index and extinction coefficient are calculated as functions of photon energy. The obtained optical data of β-LiNaSO4 crystal are used to check the validity of both Wemple-DiDomenico and Cauchy-Sellimaier dispersion relations. Normal dispersion parameters of this crystal are calculated for the first time.