Structure and refractive properties of LiNaSO4 single crystals

We report experimental results on the structure, refractive indices and birefringence of LiNaSO4 (LSS) crystals. Spectral behaviours of the refractive indices and the birefringence of LSS at the room temperature, as well as temperature and baric dependences of the birefringence are discussed. We examine the refractive indices and the birefringence using Lorentz-Lorenz and simplified Sellmeier formulae and energy-band structure calculations. Unlike LiKSO4, the birefringence of LSS decreases with increasing temperature, while accidental optically isotropic states are absent under the normal conditions. A significant increase in the birefringence of LSS, if compared with LiKSO4, is assumed to be linked with asymmetry appearing in the local second-coordination environment of the LSS structure.